COLOUR TELEVISION APPRAISAL 1956/57 FIELD TRIALSdownloads.bbc.co.uk/rd/pubs/reports/1957-31.pdf · Title SCDPE AND PDRPOSE OF THE TESTS THE QUESTIONNAIRE AND THE SYSTEM OF GRADING

Wo N 0 Sp roson. Mo A.

RESEARCH DEPARTMENT

COLOUR TELEVISION APPRAISAL

1956/57 FIELD TRIALS

Report Noo T-067

( 1957/31)

(Wo Proctor Wilson)

r '"

...

This Report is the property of British Broadcasting Corporation

the and

may Dot be reproduced in any form without the written permission of the Corpor ation •

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Report No. T-067



Title

SCDPE AND PDRPOSE OF THE TESTS

THE QUESTIONNAIRE AND THE SYSTEM OF GRADING

TEST 1

3.1. Description of the Test

3.2. Results of the Test

TEST 2

3.2.1. Results for Colour Pictures 3.2.2. Resul ts for the Reverse-·Compatible Picture 3.2.3. Comparison of Characteristics Common to the Colour

Picture and the Reverse--Compatible Picture

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4.1. Description of the Test 8

4.2. Results Expressed as Mean Gradings for the Twenty-five Sites 8 4.2.1. 4.2.2. 4.2.3.

Results for Colour Pictures, , , , , , , • Results for the Reverse-Compatible Picture Comparison of Characteristics Common to the Colour

Picture and the Reverse-Compatible Picture

4.3. Results Analysed as a Function of the Field Strength of the Individual Sites

4.3.1. "Overall Assessment of the Colour Picture" (M) 4.3.2. "Fideli ty of Colour Reproduction iI (H)

4.3.3. 4.3.4. 4.3.5. 4.3.6.

"Noise"' in the Colour Picture (DJ '

"Multiple Image Effects" (El Other Characteristics of the Colour Picture "Overall Assessment of the Reverse-Compatible

Picture"' (Dj """, .• , , , , , ,

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4.3.7. "Noise" in the Reverse-Compatible Picture (0) • , • •• 19 4.3.8. Other Characteristics of the Reverse-Compatible Picture 19

4.4. Correlation Techniques Applied to Test 2

TEST 3, PARTS H a) AND Hb) (THE "SCIENTIFIC" TESTS RADIATED FROM CRYSTAL PALACE)


5.2. Results of the Test 5.2.1. Results for Colour Pictures 5.2.2. Results for the Reverse---Compatible Picture

19

21

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22 22 24

Section Ti tle

5.2.3. Comparison of Characteristics Common to the Colour Picture and the Reverse-Compatible Picture

5.3. Correlation Techniques Applied to Test 3, Parts l(a) and l(b)

6 TEST 3, PART 2 (THE "PROGRAMME" TESTS RADIATED FROM CRYSTAL PALACE)


6.2. Results of the Test 6.2.1. Results for the Slide 6.2.2. Results for Motion Pictures 6.2.3. Results for Camera Pictures

6.3. Correlation Techniques Applied to Test 3, Part 2

7 TEST 4 (MONOCHROME CONTROL EXPERIMENT)

8

9

7.1. Description of Test


DISCUSSION • • •

8.1. Comparison of "Overall Assessment" of the Colour Pictures (M) •

8.2. Comparison of Mean Gradings of "Fidelity of Colour Reproduction" (H) • • • • • • • • • • • • • •

8.3. Comparison of Mean Gradings of "Achromaticity of the Grey Scale" (I) • • • • • • • • • • • • • • • •

8.4. Comparison of Mean Gradings of "Picture Sharpness" (J)

8.5. Comparison of Mean Gradings of ''Misregistration'' (F)

8.6. Other Features of the Colour Picture

8.7. The Reverse-Compatible Picture •••.•.

CONCLUSIONS

9.1. The Colour Picture

9.2. The Reverse-Comp atible Picture ..

10 ACKNOWLEDGEMENTS

11 REFERENCES

APPENDIX I APPENDIX II APPENDIX I II APPENDIX IV APPENDIX V .'. APPENDIX VI .• APPEl.,TDIX VII APPENDIX VIII ].I.PPElWIX IX APPENDIX X ••

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December 1957

SUMMARY

Report No. T~>067

( 1957/31)



This report gives the results of field trials of the N.T.S.C. colour television system adapted to 405 lines, which were conducted in order to assess the colour* performance of the system. Preparatory tests took place at the B.B.C. research laboratories at Kingswood and its environs, but for the major part of the trials signals radiated from the Crystal Palace transmitter were used, the programme being received over a wide area in the London region. Comprehensive data are given concerning all technical aspects of the colour picture and also the reverse-compatible picture. In addition a "control 11 experiment ".jas undertaken in which the existing monochrome service was similarly assessed for the purpose of comparison.

The results show that this particular system of colour television is capable of providing a satisfactory colour service in the frequency bands at present in use, but it is nevertheless desirable that certain features associ ated with the camera and display should be improved.

1. SCOPE AND PURPOSE OF THE TESTS

The field trials which form the subject of this report took place between 25th September 1956 and 17th May 1957, and were designed to assess critically the quality of the colour television picture which can be received in the home under ordinary viewing conditions. Demonstrations to the C.C.I.R. Study Group XI and others given in May 1956 and the following months showed that very good colour television pictures can be produced under laboratory conditions, but it still remained to be shown whether results of good quality could be obtained outside the close control of a research laboratory. It should be emphasised that the tests described relate solely to the 405-line version of the N.T.S.C.** colour television system.

In addition to those tests which were concerned with the quality of the colour picture, a control experiment was performed in June 1957, in which the picture quality of current black-and-white television was critically examined. In all, four tests were carried out and the principal features of these are given in Table 1.

Test No. 1 is not, strictly speaking, a field trial, because the receiving si te was in the same building as the transmitting equipment and the co=ection between the two was a length of coaxial cable. Nevertheless, it served to give results which should be typical of high field strength areas where ignition interference, multipath

*An assessment Of the black- and~ white compatIble picture was given in B" B .. C" Research Report No. T-062

**National Television Systems CommIttee (U. S. A..)

2

TABLE ·1

Description of the Tests

Location of Location of Vision Location of Types of No. of Test No. Picture Sources

Picture Source Transmi tter Cbaru:tel Receivers Receiver Observers

1 16 l1l1D film and slide scanner Kingswood Closed circui t 1 I Ki"il"s"<>od B.B.C. and 60

1 commercial

2 16 mm film and slide scanner Kingswood Kings;,ood I 5 i 25 si tee nearl B.B. ell 18 per site to Kingswood I I

3, Part 1 16 mm film and slide scanner Alexandra Palace Crystal Palace 1 Homes Various 144

3, Part 2 16 mm film and slide scanner Alexandra Palace Crystal Palace 1 Homes Various 267 35 mm film scanner 2 colour cameras

4 4i in. im ag e orthi con Various O.B. sites Crystal Palace 1 Kinlls;,ood Comnercial 79 cameras (monochrome) in London area

effects and noise due to low field strength (receiver noise) are completely absent. The picture-originating equipment was a 16 mm motion picture film and slide scanner1.

Test No. 2 used one of the two receivers which had been used in Test 1, and employed a 500 watt transmitter, located at Kingswood Warren, operating on Channel 5 and suitably modified to give adequate performance with the type of video signal characteristic of the adapted N.T.S.C. system 2 • The receiver was installed in a mobile laboratory, and twenty-five sites near to Kingswood were investigated. The range of field strengths was from 2' 5 mV/m to 70 f..LV/m. The twenty-five sites chosen included some typical of high field strength conditions as well as a number of places where the field was low. A few sites exhibited strong multipath interference. The attempt was made to choose sites covering the complete range of receiving conditions likely to be encountered if this system of colour television were adopted for a nation-wide service.

Test No. 3 used the Channel 1 transmitter (e.r.p. 55 kW for peak-white) located at Crystal Palace. The picture-originating equipment was located at Alexandra Palace. It consisted of a combined 16 mm film and slide scanner similar to the one at Kingswood, a 35 mm film scanner and two colour cameras each using three image orthicon camera tubes. (The 35 mm film scanner was not available at the beginning of the tests and was used for the first time on 17th April 1957.) Test transmissions took place after the termination of the normal television service on Monday, Wednesday and Friday evenings. Test No. 3 is divided into two parts. The "Monday" tests were a continuation of Tests 1 and 2 and in fact used the same slides and film material up to the end of March 1957. These tests are designated "Test 3, Part 1( a)" and are described as the "scientific" tests in contradistinction to the "Wednesday and Friday" tests which consisted principally of camera pictures of simple studio programmes and are designated "Test 3, Part 2". "Test 3, Part 1(b)" is the designation of the "Monday" tests on and after 1st April when the opportunity was taken to change the film and slides which had hitherto been in use for Tests 1, 2 and 3 Part lea). The reason for this change will be dealt with later (Section 5.1).

r 3

20 THE QUESTIONNAIRE AND THE SYSTEM OF GRADING

The questionnaire for Tests 1, 2, 3 Part l(a) and 3 Part lib) is reproduced in Appendix I and was designed to test all technical aspects of the colour picture and also the reverse-compatible black~and~white picture. The questionnaire for Test 3 Part 2 (the "programme tests) is a slightly simplified version of the previous questionnaire and is reproduced as Appendix 110 The questions on the reversecompatible picture have been deleted, as the "programme" tests were concerned exclusively with colour pictureso

The grading system permits the allocation of a score from 1 to 6 for each individual effect, as shown in the scales belowo Interfering effects such as "colour trailing due to movement:1 are assessed on scale 1, and posi tive qualities such as "sharpness"' and "'colour rendering" are assessed on scale 20

Scale 1 Score Scale 2 Score

imperceptible 1 excellent 1

just perceptible 2 good 2 defini tely perceptible but not disturbing 3 fairly good 3

somewhat objectionable 4 rather poor 4 i definitely objectionable 5 poor 5 I ~ unusable 6 very poor or absent 6

In both scales a low number indicates a favourable reaction and a high number an unfavourable reactiono

It is desirable at this point to define certain descriptive termso The phrase !'very favourable will be used when the mean grading (for a particular characteristic) is in the range 1 to 1 0 5 0 For the mean grading to give a result wi thin this range~ most of the observers must have graded the characteristic in question in grade 1 or 2; the percentage of observers in grad&s 4, 5 and 6 must be very small if the distribution is "normal"' (i.e. Gaussianl -in fact only a most abnormal distribution could give rise to such a mean grading if a substantial proportion of observations were in grades 4, 5 and 60

The term "favourable'" will be used when the mean grading is in the range A mean grading in this range will, in general, be produced when most of

the answers are in grades 1, 2 and 3, and the proportion in grades 4, 5 and 6 will usually be less than 10~o The effect will be regarded as "'favourable" because the majority of the observers will have graded the effect as grade 2, ioe. "justpercElIltible" on scale 1 or "good'" on scale 20

In the range 2 0 6 to 3'5, the interpretation of the results depends on the proportion of observations in grades 4, 5 and 6u

be regarded as "acceptable" when not more than grades 4, 5 and 60 If the number of observations the effect is regarded as "unacceptable"o

A mean grading in this range will 10~ of the observations are in in grades 4, 5 and 6 exceeds lO~,

A mean grading in excess of 3' 5 is interpreted as Viunusable"' because more than 50i of the observations will be in grades 4, 5 and 6 if the distribution is "normal VI.

\

l

4

The assumption of a "normal" distribution appears to be justified both on theoretical grounds and also on analysis of the results. A few anomalies do occur but these can reasonably be ascribed to the not very large number of observers in several of the tests. In the case of a mean grading of 2"5 or below, this mean value is itself regarded as the important parameter, because the number of observations in grades 4, 5 and 6 constitutes the "tail" of the distribution and is known to be subject to appreciable errors when the sample is small. In the range 2:6 to 3'5 the observations in grade 4 (and, to a lesser extent, 5 and 6) can no longer be described as the "tail" of the distribution and for that reason they are taken into consideration in making the assessment. The figure of 10% is arbitrary and no special claim is made for its use, other than that it is regarded as a reasonable figure to take. The following table summarises the above.

TABLE 2

Mean Grading Suggested Interpretation

1"0 to 1'5 Very favourable

1'6 to 2'5 Favourable

2"6 to 3'5 Acceptable when detailed inspection of results shows not more than 10% in grades 4, 5 and 6

Unacceptable when detailed inspection of results shows more than 10% in grades 4, 5 and 6

3"6 to 6 Unusable

3. TEST 1


Test 1 was a closed-circuit laboratory appraisal using 30 observers for each of two colour television receivers, one made by the B.B.C. Research Department 3 and the other by a radio manufacturer. The picture material consisted of one technical test slide (viz., a neutral step wedge), three colour transparencies and a portion of a 16 mm South African travel film. The colour transparencies were Ektachrome originals of size 3 in. x 2i in. (75 mm x 57 mm) of good colour fidelity and good definition. The 16 mm film was a Kodachrome duplicate of rather poor colour fidelity and of the low standard of definition associated with 16 mm film. The reason for choosing it was that it was considered typical of the usual standard of 16 mm colour film*; better film is certainly available but it was thought preferable to test the system with an average rather than a good colour film.


The mean gradings for the various characteristics are shown in Table 3, which also includes miniature histograms. Full details of the percentages of observations in each grade are given in Appendix Ill.

*Later experience showed this assumption to be incorrect (see Section 6,2.2)

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CHARACTER I STI C

A Visibility of crawling dots

B Colour synchron i sing di ffi cu I ties

C Colour trai I ing due to movement

0 Noise

E t+Jltiple image effects

F Misregistration

G Cross-co I ou r

H Fidel ity of colour reproduction

I Achromaticity of the grey scale

J Picture sharpness

K Picture brightness

L Contrast range

M Overall assessment

N Colour trai I ing due to movement

0 Noise

P Multiple image effects

o Misregistration

R Achromaticity of the picture

5 Picture sharpness

T Contrast range

U Overall assessment

5

TABLE 3

Results of Test 1

MEAN GRADINGS AND HISTOGRAMS

BBC Receiver Commercial Receiver

16 mm fi I m 511 des 16 mm fi Im 511 des

1·7 L I·g L 1·7 ~ 1·3 L 1·0 1·0 1·0 1·0

1·6 L 1·5 L 2·7 ~ 1·7 Lu--. 1·8 ~ 1·2 L 1·0 1·0 1·0 --- 1·0

2·1! LlLL. 2·1! ~ 2·1! ~ 2·2 Lll~

1·5 L 1·6 L 1·3 L I·I! L 3·1 ~

2·6 ~ 2·8 ~

2·3 JL. 3·1! .llu.... 3·1 JLL.

2·3 ~ 2·2 L 2·3 lL-.- 2·1! ~ 2·0 ~ 1·7 ~ 2·1 ~ I·g Lh.--

2·7 ~ 2·7 ~

2·6 .lh.- 2·1! lL 2·1! JL--. 2·2 ~

I·I! L 1·3 L I·g ~ 1·5 L 1·3 L 1·3 L 1·0 1·0 1·0 ---- 1·0

2·1 ~ I·g ~ 2·1! ~ 2·7 ~

2·2 L1L-. 2·2 L1L-- 2·1! ltL.- 2·6 ~

2·1 ~ 2·2 ~ 2·3 ~ 2·7 ~

2·1! ~ 2·5 ~

2·1 ~ 2·2 L 2'5 1L-. 2'8 .1L

6

Characteristics A to M relate to the colour pictures and characteristics N to U to the reverse-compatible bla.ckc"'and~white picture.

3.2.1. Results for Colour Pictu~es

Dealing first with the B.B.C. receiver, it will be seen from Table 3 that when static slides are viewed, the mean gradings for the colour pictures vary from 1"0

to 3' 4. In the "very favourable; category are "colour synchroni sing difficulties" (Bl, and limultiple image effects)' (E) in the "favourable" category are "visibility

of crawling dots" (A), "noise" (Dj, "misregistration IF), "cross---colour" (8), "picture sharpness" (J),'picture brightness" ;K), and "overall assessment" (M). HFidelityof

colour reproduction" (H) , "achromaticity of the grey scale' I) and "contrast range" (1) are in the "unacceptable I: category (Table 21. It will thus be seen that the

"overall assessment" was "favourable" although three of the individual characteristics were "unacceptable",

Motion pictures viewed in colour on the same receiver gave rise to mean

gradings varying from 1'0 to 3' 1. In the:very favourable category we find "colour synchronising difficulties (El 'mult,iple image effects' Ei and 1:cross~colour)1 (8):

in the "favourable' category are "visibility of crawling dots" A), "colour-~trailing

due to movement (C;, 'misregistration l 'F) 'pict'clre sharpness J) and "picture brightness (K) • "Noi se" (Dj, "fidelity of :colour reproduction iH j and 'overall

assessment" (M) are "unacceptable"" Tne change in g::-ading of the noise :D) from 1"7 to 2-7 when changing from slides to motion pi:.;tures is quantitatively consistent with

the relative areas of slide and 16 mm film and tbe relati'7e apertures of the two optical systems 1.

The assessment of the colour pictures on the :::ommercial receiver gave rise to similar mean gradings. For the static slides, the mean gradings vary from 1-0 to

3"1. In the "very favourable" category are visibility of crawling dots" (A),

IIcolour synchroni sing difficulties :B) j "noi se" CD}, "multiple image effects" (E) ~ and "cross-colour" :8) in the "favourable" class are "misregistration" (FJ, "fideli ty of colour reproduction' (Hj, "picture sharpness (Ji, "picture brigbtness"

(K) and "overall assessment" (MI. "AchromaticicY of the grey scale (1) and "contrast

range" (1) are "unacceptable". The overall assessment of the colour pictures on the commercial receiver is slightly better than that of the B.B.C. receiver. The sharp

ness of the pictures is not quite as good, but 'vi sib11i ty of crawling dots", "noise"

and "cross-colour" are more favourably rated in the case of the commercial receiver.

Motion pictures viewed on the commercial receiver are described by mean gradings which vary from l' 0 to 2' 8. The following characteristics are in the "very

favourable" class: "colour synchronising difficulties ;B), "colour-trailing due to movement" (Cl, "multiple image effects); IE I , and ;'cross--colour'; (8), In the "favour

able" class are "visibility of crawling dots' :A), "noise (D),misregistration" (F)

"sharpness 11 (J), librightness (K) j and overall rating (MI. "Fidelity of colour

reproduction" (H) is the only characte:,istic in the 'unacceptable" class (25% of

observers in grades 4, 5 and 6'0

Comparing the two receive:::'s for both motion pictures and slides, it is seen

that the commercial receiver has slightly better gradings on several characteristics

(including the "overall assessment') although its sharpness is slightly less good than that of the B.B.C. receiver ,as judged on static slides but not on the 16 mm motion

picture) •

r 7

3.2.2. Results for the Reverse-Compatible Picture

Inspection of Table 3 shows that the reverse-compatible picture was graded

favourably on theB.B.C. receiver both for slides and motion pictures. In the case of the slides, ;'multiple image effects (P) are in the "very favourable/; class and all the remaining characteristics are in the "favourable E class. For motion pictures (B.B.C. receiver) we find that "colour trailing due to movement" (N) and "multiple image effects il (P J are in the "very favourable" class and all the other characteristics are in the "favourable class. "unusable" class (Table 2).

No characteri sti c is in either the "unacceptable" or

The commercial receiver did not give as good a reverse-compatible picture as the B.B.C. receiver. Static slides viewed on the commercial receiver gave rise to mean gradings in the "very favourable I; class for "noise"{O), and "multiple image effects" (PI, but the remaining characteristics,viz.,I'misregistration" (Ql, "achromaticity of the picture (R), "picture sharpness· (S) and '"overall assessment" (D) were in the "unacceptable" class. "Contrast range' (T j was in the "favourable" class, although on the lower boundary. Motion pictures viewed on the commercial receiver gave rise to "'very favourable" mean gradings for "colour trailing duetomovement" (N),

"noise" (0), and "multiple image effects" (P) and "favourable" mean gradings for "misregistration" (Q), "achromaticity" (Ri, "picture sharpness;) [Si and "overall assessment (D). It is reasonable to assume that the added interest due to movement has caused the "unacceptable" mean gradings for static slides to move into the "favourable" class.

We may thus conclude from this test that the reverse-compatible picture is always acceptable on the B.B.C. receiver, but is acceptable on the commercial receiver only when moving pictures are shown.


Eight of the characteristics are common to the colour picture and the revers~-compatible black-and-white picture, and it is of interest to examine the differences between the mean grading~ for motion pictures and slides. This has been summarised in Table 4 for both receivers.

TABLE 4

Test 1

Difference of Mean Gradings

Characteristics Compared BoB.Co Receiver Commercial Receiver

Film Sli,des Film Slides

C-N Colour trailing due to movement 0'2 - 0'2 -D-O Noise 0'9 0'2 0'5 -0'1 E-P Multiple image effects 0'0 0'0 0'0 0'0 F-Q Mi sregi stration 0'3 0'5 O@O -0@5

I-R Achromaticity of the picture ~ 1@2 - 0'5 J-S Picture sharpness 0'2 0'0 -0@1 -0'3 Ir-T Contrast range ' . 0'3 - 0'2

M-D Overall assessment 0'5 0@2 -O'l -0'6 A positive difference means that the re~erse~compatible picture is better than the colour picture since a 10y score means a fa~ourable res'.ctlon

I L

8

The largest change is in the achromaticity of the picture (I-R), where the B.B.C. receiver is improved by 1'2 units and the commercial receiver by 0'5 units when the colour circuits were switched off. This would imply incorrect alignment of the red, green and blue signals making up the neutral scale at either the transmitter or receiver. It must be admitted that one of the most difficult tasks to accomplish is the attainment of a really good neutral scale on a colour receiver.

slides. "Noise" (D-O) changes appreciably for motion pictures although not for

This is due to the fact that 16 W~ motion picture film gives rise to a higher level of noise than do slides, and the presence of the chrominance signal causes the visibility of the noise to be increased.

The "overall assessments" change in opposi te directions for the B.B.C. receiver and the commercial receiver. Thus. the B.B.C. receiver gives a better black-and-white picture than colour picture, but the reverse is true for the commercial receiver.

Other comparable features are not significantly changed, as between the colour picture and the reverse-compatible one.

4. TEST 2


This test made use of a 500 watt transmitter installed at Kingswood Warren and operating on Channel 5. Channel 5 was chosen so that the tests could be made during normal television service hours. The B.B.C. receiver used in Test 1 was installed in a mobile laboratory. Twenty-five sites in the vicinity of Kingswood, Surrey, were chosen and the locations of these are given on the map, Fig. 1. As will be seen, twenty-two of the twenty-five sites were within a radius of 5 miles (8 km) from the transmitter. A team of three observers recorded their observations at each site, the programme for the test transmissions being identical with that used in Test 1. The same picture-originating equipment was used and also the same slides and film.

The results of this test can be analysed in two ways:

(1) Mean gradings for each individual site for each characteristic averaged for the twenty-five sites.

(2) The gradings for each individual site for each characteristic can be analysed in terms of the measured field strengths.

Both methods will be used but when using method (1) it should be borne in mind that the proportion of sites which have low field strength (i.e. less than 200/-LV/m) is much greater than that for a typical service area. Hence, the mean gradings are likely to be less favourable (i.e. numerically greater) than those for Test 1 or Test 3.

4.2. Results Expressed as Mean Gradings for the Twenty-five Sites

The following table gives the mean gradings and histograms for the twentyfive sites taken as a whole. Detailed information on the percentage of observations in each grade will be found in Appendix IV.

-

5ite numbers ore indicated thus: +3 Circlu of 1,2,3 dc. miles radius are centred on the transmitter at Klngswood

Fi g. I - Location of si tes used in Test 2

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D

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F

G

H

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K

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TABLE 5

Results of Test 2

CHARACTERISTIC MEAN GRADINGS AND HISTOGRAMS

16 mm f i I m SI ides

Visibi I ity of crawl ing dots I·g t 2·2 ~

Colour synchronising difficulties 1·0 I·lj L Colour trai I ing due to movement I·g ~

Noise 3·6 -tllL 3·0 ~

Multiple image effects 2·0 ~ I·g ~

Misregistration 2·5 ~ 2·3 ~ Cross-co t DU r 2·2 ~ 2·2 ~

Fidel ity of colour reproduction 3·5 .JL 2'9 ~

Achromaticity of the grey scale 3·0 ~

Picture sharpness 2'9 L 2·5 ~ Picture brightness 2·1 ~ I·g L Contrast range 2·3 ~ Overall assessment 3·lj ~ 2'9 ~

Colour trai I ing due to movement 1·6 ~ Noise 2·8 ~ 2·6 ~ Multiple image effects I·g ~ I·g ~

Mi sreg i strat ion 2·6 lL-.- 2·2 lL. Achromaticity of the picture 2·1 ~ I·g L Picture sharpness 2·7 ~ 2·lj ~ Contrast range 2·1 L Overall assessment 2·8 ~ 2·5 k

,

4.2.1. Results for Colour Pictures

Considering the results for the static slides first, we see from Table 5 that the mean gradings vary from 1'4 to 3'0. The only characteristic which is in the "very favourable" class is "colour synchroni sing difficul ties" (B). "Visibility of crawling dots" (A) , "multiple image effects" (E), "misregistration" (F), "crosscolour" (G), "picture sharpness" (J), "picture brightness" (K) and "contrast range" (L) are all in the "favourable" class. "Noise" (D), "fidelity of colour reproduction" (H), "achromaticity of the grey scale" (I) and "overall assessment" (M) have mean gradings in the "unacceptable" class.

In the assessment of motion pictures, Table 5 shows that the mean grading for "colour synchronising difficulties" (B) is the only characteristic in the "very favourable" class. In the "favourable" class we find "visibili ty of crawling dots" (A), "colour trailing due to movement" (C), "multiple image effects" (E), "misregistration" (F), "crosscolour" (G) and "picture brightness" (K). "Picture sharpness" (J) has a mean grading in the "acceptable" class: "fidelity of colour reproduction" (H), and "overall assessment" (M) are in the "unacceptable" class. "Noise" (D) is in the "unusable" class wi th a mean grading of 3' 6.

The fact that the "overall assessments" for both film and slides have been graded as "unacceptable" indicates the shortcomings of this method of analysis which places too much weight upon results from sites of

r 11

low field strength. Nevertheless, it has been included because Tests 1 and 3 are analysed in this way.


Table 5 shows that the range of mean gradings for slides when viewing the reverse-compatible picture is 1'9 to 2'6. "Noise" (0) is the only characteristic with a mean grading in the Hunacceptable" class: all the remaining characteristics are in the "favourable" class, including the "overall assessment".

For motion pictures, the range of mean gradings varies from 1'6 to 2'S and the following characteristics have mean gradings in the "favourable" class: "colour trailing due to movement" [N), "multiple image effects" (PI, and "achromaticity of the picture" (R). "Misregistration" (Q) and "picture sharpness" (S) are judged to be

"acceptable".

In the "unacceptable" class of mean gradings we have "noise" (0) and "overall assessment" (U).


Table 6 lists the eight characteristics common to both colour and reversecompatible pictures, and gives the differences in mean grading.

TABLE 6

Test 2

Differences of Mean Gradings Characteristics Compared

Film Slides

C-N Colour trailing due to movement 0'3 -D-O Noise O'S 0'4 E-P Multiple image effects 0~1 0-0 F-Q Misregistration -0"1 0'1 I-R Achromaticity of the picture - 1'1 J-S Picture sharpness 0'2 0'1 lr-T Contrast range - 0'2

M-U Overall assessment 0-6 0'4 A positive difference means that the reverse-coMpatible picture is better than 'the colour picture

One of the features which the mobile laboratory tests were designed to investigate was that of "multiple image effects il (E--P) and it is of interest to note

that the difference between the results for colour and for reverse-compatible reception is negligible. This situation is also found to be true if the data for the individual sites are examined (Section 4.3.4).

Most of the other common characteristics are also found to give rise to small differences in mean grading. The exceptions are "achromaticity of the picture" (I-R) , "noise" (D-O) and "overall assessment" (M-U). These were also the character-

12

istics giving significant differences in Test 1 (see Table 4, B.B.C. receiver). For these three characteristics the reverse-compatible picture gives a better result than the colour picture.

4.3. Results Analysed as a Function of the Field Strength of the Individual Sites

In addition to setting up the apparatus and observing the programme of slides and film on the colour receiver, the field strength of the radiation from the Channel 5 transmitter (located at Kingswood) was measured at each of the twenty-five sites. As previously stated, the values ranged from 2'5mV/m to 70/LV/m. The gradings for each characteristic given by the three observers were averaged for each site and hence data are available from which the mean grading for any characteristic can be plotted against the field strength. This has been carried out for the most significant characteristics and is described below.

4.3.1. "Overall Assessment of the Colour Picture" (M)

The mean gradings for the "overall assessment" of the slides at each site are shown in Fig. 2 as a function of the field strength: a linear scale is used for the mean grading and a logarithmic scale for the field strength. Apart from two points which relate to the observations at sites 20 and 23 (see Appendix V for full details of the twenty-five sites), the points lie on a broad locus which can be seen to change in slope at about the 150/LV/m level. Statistical analysis has shown that there is no significant correlation between the mean grading and the field strength for field strengths above 150 /L V/m. The line BC (Fig. 2) shows the "best" straight line* for those points representing field strengths greater than 150 /L V/m. It will be seen that on this basis the grading is not greatly influenced by the field strength. On the other hand, for field strengths of less than 150/LV/m, there is· a significant

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FlelCl strength at 22ft 0.9.1" millivolts per metre

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Fig. 2 - Colour sI ides; "overall assessment" (M) plotted as a function of field strength

*"Best" in the sense of minimum value of the sum of the squares of deviations

r

...

13

correlation between the mean grading and the field strength. The "best ii straight line for the points in this range of field strength is shown as the line AB in Fig. 2. This line would imply that below about 100/-LV/m the signal is "unusable" (as defined in Table 2).

Fig. 3. The corresponding data for viewing motion pictures in colour are given in The spread of points is somewhat greater, as might be expected, but the

division at 150/-LV/m no longer applies, inasmuch as there is no significant correlation of the variables when analysed into the two classes viz., above and below the field strength of 150/-LV/m. If the data over the whole range of field strengths are statistically analysed, there is a significant correlation between "overall assessment" and field strength. The straight line shown in Fig. 3 gives the "best" linear relationship between the mean grading and the logarithm of the field strength. Owing to the poor quality of the film, the "overall assessment \1 never reaches the "favourable" class and it becomes "unusable" at about 350 /-LV/m.

4.3.2. "Fidelity of Colour Reproduction; (HI

This characteristic is the most important single variable of the system: Fig. 4 shows how the "fidelity of colour reproduction of the slides (characteristic H) varies with the field strength. Although there is considerable spread of the points, the colour fidelity changes only slightly as the field strength is reduced. Unlike Fig. 2 it shows no evidence of a sudden change of slope at low field strengths and the straight line of Fig. 4 again represents the ;;best linear relationship between the mean grading and the logarithm of the field strength. Over the whole range of field strengths used in this test there is only half a grade change of opinion about the fidelity of colour reproduction.

In the case of motion pictures, the results are shown in Fig. 5, and the same feature is again noticed, viz., slight change of grading with considerable change of field strength. The spread of points in Fig. 5 would appear to be slightly less than that shown in Fig. 4, which is a little unexpected, as greater precision of judgement is usually possible with slides than with motion pictures.

4.3.3. "Noise ll in the Colour Picture (DJ

The relationship between the subjective estimate of "noise" (characteri stic DJ and the field strength is shown in Fig. 6 for the static slides. Apart from sites 20 and 23, which have previously been noted as giving somewhat anomalous results (Section 4.3.1), the points lie on a curved locus showing that, as the field strength is reduced, the gradient of the curve increases. Thus, a given fractional decrease in field strength produces larger differences of grading as the field strength diminishes. The noise appears to be "favourable" for field strengths exceeding 400/-LV/m and to be "unusable" at levels less than 170/-LV/m. This latter figure is higher than that derived from the "overall assessment (Section 4.3.1).

The results for motion pictures are shown in Fig. 7. Sites 20 and 23 again give anomalous results and the remainder of the points lie on a curved locus. It will be noted that in this instance noise associated with the picture source prevents the mean grading from becoming less than 3"0 at field strengths above 0'5 mV/m; below this field strength the noise increases in much the same way as described for slides. The noise of the colour picture derived from this 16 mm film is apparently "unusable" for field strengths below about 230 /-LV/m •

I ......

14

" " .. 3 :E

I (1-05

t-

0 0

r----I--- 0

r--ro 10-1- t:---.... 0 ~

().S 1·0

field strength at 22ft a.g.l., millivoll! per metre.

Fig. 3 - Colour motion pictures; "overall assessment" (M) plotted as a function of field strength

" " .. :E 3

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~

0

0

01

0

0

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Field strength at 22ft a.g.l., m~livolts per metre

Fig. ~ - Colour sI ides; "fidel ity of colour reproduction" (H) plotted as a function of field strength

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Field slrenglh al 221l. a.g.l., millivolls per melre

Fig. 5 - Colour motion pictures; "fidel ity of colour reproduction" (H) plotted as a function of field strength

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neld slrenglh al 22fl.a.g.l.,millivolls per melrt.

Fig. 6 - Colour sI ides; "noise" (0) plotted as a function of field strength

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I Silo 10 I~

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& ....... 0

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00

O·S to S-O Fiold slrength Qt 11ft Q.\>I.,millivolt. por motro.

Fig. 7 - Colour motion pictures; "noise" (0) plotted as a function of fi el d strength

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Fig. 8 - Reverse-compatible sI ides; "overall assessment" (U) plotted as a function of field strength

r

17

4.3.4. "Multiple Image Effects" (E;

No significant correlation is found to exist between the field strength at a site and the presence of multipath interference. It is not to be inferred that this is generally true and it may be characteristic only of the disposition of the particular sites chosen. One very significant fact, however, is that multiple image effects in colour (characteristic E) when they exist give rise to much the same grading as multiple image effects in reverse~compatible pictures {characteristic PI. To illustrate this, the five sites which revealed the most serious multiple image effects have been listed in Table 7. which shows the mean gradings for colour and reverse-compatible pictures obtained from slides.

TABLE 7

Test 2

Mean Gradings Site No.

Characteristic E Characteristic P Difference ~P

4 2'7 3'2 ~0'5

12 3'2 2-8 +0·4 23 3'7 3'7 0'0 24 3'0 3'0 0"0 25 3'3 3'0 ';-0·3

From this it will be seen that the differences in grading do not exceed half a grade and they are not consistently in anyone direction.

4.3.5. Other Characteristics of the Colour Picture

The other characteristics of the colour picture do not show any significant correlations when examined in terms of the field strength at the site. This lack of correlation is certainly desirable in the case of "colour synchronising difficulties" (B) and is not unexpected in such characteristics as "colour trailing due to movement" (C), "misregistration (Fl, "achromaticity of the grey scale" (I).

Mention should be made of the fact that at one of the twenty~five receiving sites (site 6) there .ras difficulty in obtaining a colour picture. The chrominanceto-luminance ratio was so low for the first position of the mobile laboratory at site6 that the chrominance circuits failed to operate. Upon moving the mobile laboratory about 100 yards, the ratio of chrominance to luminance increased and the colour synchronisation operated properly. This was the only site where difficulties of this sort were encountered.

4.3.6. "Overall Assessment of the Reverse~Compatible Picture" (U)

The results for the "overall assessment" of the reverse-compatible picture (characteristic U) plotted as a function of the field strength are shown in Fig. 8 for slides and Fig. 9 for motion pictures. Dealing with the slides first, we see that there is evidence of a change of slope at a field strength of 150,LCV!m in the "best"

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Field strength al Zllta.g.l.millivolts per metre_

Fig. 9 - Reverse-compatible motion pictures; "overall assessment" (U) plotted as a function of field strength

Field strength at 12ll-a_9-I_. milllvolts per metre

Fig. 10 - Reverse-compatible sI ides; "noise" (0) plotted as a function of field strength

19

straight line representing the points. AB (Fig. 8) is the "best" straight line for the points with field strengths of less than 150 ,u V/m and BC represents the points with field strengths above 150,uV/m. Above 150,uV/m the change of grading is slight as the field strength increases, but the slope of the line BC is steeper. The pictures are "unusable" below about 80,uV/m and the overall assessment is "favourable" above 150,uV /m. In calculating the line BC, the points relating to sites 20 and 23 have been ignored.

There is no evidence in the motion picture results (Fig. 9) to suggest a change of slope at 150 {.LV /m and the straight line shown in Fig. 9 represents the "best Ii linear relationship between the mean grading of characteristic U and the logarithm of the field strength. The grading is "favourable" above a field strength of 1· 4 mV/m and becomes "unusable" below 70 {.LV/m.

4.3.7. "Noise" in the Reverse-Compatible Picture (0)

The graphs relating to "noise" as a function of field strength are shown in Fig. 10 (slides) and Fig. 11 (motion pictures).

The results for slides (Fig. 10) show features similar to those of the corresponding graph for colour pictures (Fig. 6;. Sites 20 and 23 give points that are removed from the main locus. The noise is graded "unusable" for field strengths below 110,uV/m and "favourable" for field strengths above 280,uV/m.

The results for motion pictures (Fig. 11) show a more or less constant mean grading of 2'3 for field strengths above 400,uV/m. The noise result for motion pictures is "favourable" above 250,uV/m and becomes "unusable" below 120 ,uV/m. These figures are similar to those for static slides (vi z" 280 and 110 ,u V/m).

4.3.8. Other Characteristics of the Reverse-Compatible Picture

With the exception of noise (Section 4.3.7) none of the characteristics of the reverse-compatible picture correlates significantly with the field strength and for that reason no detailed results will be quoted: the mean gradings and histograms for the twenty-five sites have already been given in Table 5.

4.4. Correlation Techniques Applied to Test 2

Statistical methods can be used to find out how the "overall assessment" depends on the various characteristics listed in the questionnaire. Partial corre-lation coefficients can be calculated giving the correlation existing between two variables when all the other variables in an experiment are held constant. This type of analysis has been carried out for the colour versions of both the slides and the motion pictures and gives some interesting results. It shows that the characteristics which determine the "overall assessment 11 are principally the "fide"li ty of colour reproduction" CH), the "noise" (D) and ''multiple image effects" (Ei. An equation has been constructed, with the above three characteristics as variables, which enables the "overall assessments" for Test 2 for each site to be calculated with a fair degree of certainty. The equation for the assessment of slides is:

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Fig. I1 - Reverse-compatible motion pictures; "noise" (0) plotted as a function of field strength

r 21

(1)

where the letters M, H, D and E are used to imply the numerical gradings of the characteristics. This equation applied to the mean gradings for each site gives a correlation coefficient of 0"S9 when the calculated values of M are compared with the experimental ones. The coefficients of the variables are important, not so much for their absolute values, as for their relative values.

The equation for the assessment of motion pictures in colour is:

M = 1" OSH + 0"59D+0'13E- 2"S2 ( 2)

When the calculated and experimental values are compared, a correlation coefficient of 0"S7 is found. The same three variables are involved as for the slides and are in the same order of importance, but with somewhat different relative coefficients. To compare the coefficients, the sums of the coefficients for each equation can be normalised and the importance of the variables is then as follows:

TABLE S

Test 2

Relative Importance Characteristic

Slides Motion Pictures

H Fidelity of colour reproduction 52% 60% D Noise 28% 33% E Multiple image effects 20% 7%

From this table, it is seen that "fidelity of colour reproduction" (H) and "noise" (Dj are more important for motion pictures than for slides: this indicates that the fideli ty of colour on the film was less good than that of the slides, likewise the signal-to-noise ratio of the film is less than that of the slides. Multiple image effects contribute more to the slides than to the motion pictures and this is reasonable since multiple images can be perceived more easily on still pictures.

It is suggested that a colour television system has reached its final objective when the only variables in the equation describing the "overall assessment" are "noise" and "multiple image effects". These effects are fundamental to a telecommunication problem. As long as any other variables are present, some measure of improvement should in theory be possible.

5. TEST 3, PARTS l( a) AND 1(b) (THE "SCIENTIFIC" TESTS RADIATED FROM CRYSTAL PALACE)


Test 3 used the transmitter located at Crystal Palace, radiating 55 kW e.r.p. for peak-white on Channel 1: the picture~originating equipment was located at Alexandra Palace and colour receivers of various kinds were installed in the homes of

p

i

22

B.B.C. engineers, and in the laboratories and homes of engineers of various radio manufacturers who participated in this experiment through the auspices of B.R.E.M.A. As previously explained, Test 3, Part 1, relates to the "Monday" transmissions from Crystal Palace and the subdivision into Parts l(a) and l(b) signifies the change of programme material which took place on 1st April 1957. The transmissions from November 1956 to March 1957 were a continuation of Tests 1 and 2 in that the programme and the picture material remained unchanged. Early in 1957, however, it was felt that improved results might be obtained if more attention were paid to the colour rendering of the film used. It is well known that colour film loses much in the duplicating process, and so the B.B.C. Research Department made a 16 mm colour film which was used in original form from 1st April 1957 onwards, in place of the commercial duplicate which had been used up to the end of March 1957. A new set of slides was also chosen.

An opportunity was also taken at this time to make one or two improvements to the colour receivers used in the test.

The number of completed questionnaires received during the November 1956-March 1957 transmissions [Test 3, Part l(a)] was 112 for the period April~May 1957 [Test 3, Part Hb)] the number of completed questionnaires was 32.


" The mean gradings for the various characteristics are shown in Table 9, which also includes histograms. grade are given in Appendix VI.

Full details of the percentages of observers in each

5.2.1. Results for Colour Pictures

The mean gradings for the slides will be considered first. For Part l{a) it will be seen from Table 9 that the mean gradings range from 1" 2 to 3'0: in the "very favourable class (Table 2) are found "colour synchronising difficulties)! (B),

"noise" (D), and "multiple image effects" (E). Continuing our examination of Part Ha), slides, the following characteristics are in the "favourable" class: "visibility of crawling dots" (Al, "misregistration'I (Fi, "cross~-colour" (G), "picture sharpness" (J), "picture brightness" (K), and "overall assessment" (M). Three characteristics have mean gradings in the "unacceptable" class, viz., "fidelity of colour reproduction" (H), "achromaticity of the grey scale" (I), and "contrast range" (L). The fact that fidelity of colour reproduction gives a mean grading in the "unacceptable" class must be attributed mainly to the performance of the receivers, because the slides themselves are of good quality in this respect and demonstrations at Kingswood have shown that the colour television reproduction can compare very favourably with that of the same slide when optically projected.

The mean gradings for Part Hb), slides, will be seen from Table 9 to have improved somewhat as compared with Part l(a). The range of mean gradings is now 1'1 to 2'4 and hence no characteristic is in classes other than "very favourable" or "favourable". In the "very favourable" class we find "visibility of crawling dots" (A), "colour synchronising difficulties" (B), "noise" (Dj, "multiple image effects" (E), and "cross-colour" (G). The remaining characteristics are in the "favourable" cl ass and these are nmi sregistration"' (F), "fidelity of colour reproduction" (H J ,

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et: :::> o -' o u

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TABLE 9

Results of Test 3, Parts lea) and l(b)


CHARACTERISTIC Part I a Part

16 mm f i I m SI ides 16 mm f i I m

A Visibi I ity of crawl ing dots 1·5 L 1'8 ~ 1'1 L B Colour synchronising difficulties 1'2 L I·I! L 1·0 L C Colour trai I ing due to movement I·I! L 1·2 L D Noi se 2·7 WL.. I·I! L 1·2 L E Multiple image effects 1·2 L. 1·2 L 1·1 L F Misregistration 1·8 LL........ I·g Lh....... 1·8 LL--G Cross-colour 1·6 L 1·7 ~ 1·2 L H Fidel ity of colour reproduction 3·1 dJL 2·6 ~ 2·2 lL I Achromaticity of the grey scale 3·0 J.lL

J Pi cture sharpness 2·6 JL.... 2·1! elL 2'1 ~ K Picture brightness 2·1! ~ 2·1 ~ 2·0 L L Contrast range 2·6 lh--. M Overall assessment 3·0 ~ 2·5 JL 2'1 L

N Colour trailing due to movement 1·3 L I·I! L o Noi se 1·7 ~ 1·2 L 1·1 L P Multiple image effects 1·2 L 1·2 L 1·2 L o Misregistration 2·0 LlJ----. I·g Lh....... 2·0 liL... R Achromaticity of the picture 2'1 ~ 2·2 ~ I·g ~ S Picture sharpness 2·1\ J.L.--. 2·1! ~ 2·1 L1L. T Contrast range 2·6 ~

U Overall assessment 2·6 ~ 2·5 lL 2·3 1L-

23

I b

SI ides

1'3 L 1·2 L 1·2 L 1·1 L I·g L 1·3 L 2·3 ~ 2·1! JL....

2'1 L I·g L 2·2 L 2·3 L

1·0 L 1·1 L I·g ~ 2·0 L 2·1 L 2·1! elL.... 2·2 L

24

"achromaticity of the grey scale" (I), "picture sharpness" (J), "picture brightness" (K), "contrast range" (L) and "overall assessment" (M). Although the colour slides were changed between Parts lea) and l(b), the quality of slide was excellent in both cases. The improvement in the mean gradings must be primarily due to improved performance of the receivers, part of which may well be due to the experience gained in operating them during the six months of the transmissions and al so to the modifications which were made to some of the receivers (Section 5.1).

The mean gradings for motion pictures in Part lea) range from 1"2 to 3·1. "Visibility of crawling dots" (A), "colour synchronising difficulties" (E), "colour trailing due to movement" (C), and "multiple image effects" (El are in the "very favourable" class. Characteristics with mean gradings in the "favourable" class are "misregistration" (Fl, "cross-colour" (G) and "picture brightness" (K). "Picture sharpness" (J) is t'acceptable" but "noise" (D), "fidelity of colour reproduction" (H)

and "overall assessment" (M) are "unacceptable".

The mean gradings of all the "unacceptable" characteristics in Part l( a) (motion pictures) improve considerably, as will be apparent when the results of Part l(b) (motion pictures) are examined. The range of mean gradings is 1" 0 to 2" 2,

which range will be observed to be slightly better (i.e. numerically less) than the range for the mean gradings of slides in Part l(b). Characteristics in the "very favourable" class are "visibility of crawling dots" (A), "colour synchronising difficul ties" (B), which are virtually non-existent, "colour trailing due to movement If (C), "noise" (D), "multiple image effects" (E), and "cross-colour" (G). The characteristics with mean gradings in the "favourable" class are ''misregistration'' (F), "fidelity of colour reproduction" (H), "picture sharpness" (J), "picture brightness" (K), and "overall assessment"(M). "Noise" (D), "fidelity of colour reproduction" (H) and "overall assessment" (M) are characteristics which have all improved by the order of one grade as between Part 1(a) and Part l(b). Much of this improvement can be directly attributed to the change of film. Further evidence on the effect of change of film on mean gradings will be found in Section 6.2.2.


Table 9 shows that the mean gradings for slides in Part lea) ranged from 1" 2 to 2" 6. Only one characteristic was graded as "unacceptable" and that was "contrast range" (T). The "overall assessment" (U) is in the "favourable" class, al though on the border thereof. Other characteristics in the "favourable" class are "misregistration" (Q), "achromaticity of the picture" (R), and "picture sharpness" (S). The two characteristics with mean gradings in the "very favourable" class are "noise" (0), and "mu 1 tiple image effects" (P).

An improvement (i.e. numerical reduction) in all mean gradings for slides is seen when the Part l(b) results are compared with the Part lea). All the mean gradings for slides in Part 1(b) are in ei ther the "very favourable" or the "favourable" classes. Thus, we have "noise" (0), and "multiple image effects" (P) in the "very favourable" class with all the other characteristics in the "favourable" class. The "overall assessment" is no longer on the border of its class, but has a mean grading of 2" 2.

The results for motion pictures in Part lea) show mean gradings ranging from 1"2 to 2"6. "Colour trailing due to movement" (N), and "multiple image effects" (P) are in the "very favourable" class. "Noise" (0), "misregistration" (Q), "achroma-

-25

tici ty of the picture" eR), and "picture sharpness" (S) are in the "favourable" class. The "overall assessment" is "acceptable", since 10% of the observers use grades 4, 5 and 6 to describe it. The results for motion pictures in Part l(b) show a general improvement over the corresponding results for Part l(a), the most noticeable of which is the mean grading of "noi se" (0). The range of mean gradings is 1'1 to 2'3. Three of the characteri stics are in the "very favourable" class, vi z., "colour trailing due to movement" (N), "noise" (0) and "multiple image effects" (P). The remaining characteristics are in the "favourable" class, viz., ''misregistration" (Q), "achromaticity of the picture" (R), "picture sharpness" (S), and "overall assessment" (U).


The eight characteristics common to the colour and the reverse-compatible pictures are listed in Table 10, which gives the differences in mean grading.

TABLE 10

Test 3, Parts l( a) and Hb J

Differences of Mean Grading

Part l( a) Part Hb) Characteri stics compared

Motion Motion Slides Pictures Slides Pictures

C-N Colour trailing due to movement - 0'1 - -0'2 D-O Noise 0'2 1'0 0-2 0-1 E-P Multiple image effects 0-0 0-0 0'0 -0-1 F-Q Misregistration 0'0 -0-2 0'0 -0-2 I-R Achromaticity of the picture O'S - 0-4 -J-S Picture sharpness 0'0 0'2 0'0 0-0 L-T Contrast range 0-0 - -0-2 -

M-U Overall assessment 0'0 0'4 0'1 -0-2

A positive difference means that the reverse~compatlble picture is better than the colour picture

Many of the common characteristics are not significantly different; thus we have "colour trailing due to movement", "multiple image effects", "misregistration", "picture sharpness" and "contrast range", which give the same mean gradings for colour

and for the reverse-compatible pictures to within to' 2 of a grade. "Noise" does not change except for Part l(a), motion pictures, where there is l'Oof a grade difference. The achromaticity of the neutral scale changes by O· 4 of a grade in Part l(b) as compared with O'S of a grade in Part l(a). This is a desirable reduction since the swi tching off of the colour circuits should produce a negligible change in achromaticity if the three channels of the receiver (and transmitter) are properly balanced. The "overall assessment" exhibits only slight changes of grading except for Part 1(a), motion pictures. In Part l(b), motion pictures, there is 0'2 of a grade improvement in the colour picture as compared with the reverse-compatible picture.

5.3. Correlation Techniques Applied to Test 3, Parts l(a) and l(b)

Following the method outlined in Section 4.4, the individual data from this test were analysed and four equations built up to express the way in which the "overall

26

assessment" (M) was derived from those variables which had significant partial correlation coefficients with the "overall assessment iI (M).

The equation derived for slides viewed in colour for Part lea) is:

The correlation coefficient betlveen the calculated values of M and the experimental values is 0'78. The parameters wtich influence the judgement of the observers are, in order of importance, "fidelity of colour reproduction" (H), "picture brightness" (K),

"misregistration" (F) and "picture sharpness" (JJ. It is to be noted that these parameters are not the same ones which appeared in equation (1) (Section 4.3). "Fidelity of colour" is still the most important variable, but instead of "noise" and "multiple image effects il which were the significant parameters in Test 2, we now find that three other variables are important, viz., K, F and J. "Noise" and "multiple image effects" are no longer important, because in Test 3 all the receiving sites are wi thin the primary service area of the Crystal Palace transmitter; "multiple image effects" do not contribute significantly, because very few of the receiving sites suffered from this trouble. The variables which are significant are in agreement with known facts. Thus, picture brightness on a shadow mask tube is of the order of 10 ft-L and compares unfavourably wi th present~day monochrome tubes. "Misregistration" is a well-known difficulty and it is not surprising that it should contribute to the "overall assessment". That it was not significant in Test 2 can be attributed to the fact that a skilled engineer present at each site adjusted the registration to the optimum. "Picture sharpness is the least important of the parameters. The 21 in. shadow mask tube (RCA type 21AXP22) has 400,000 triads of dots, but this number is not sufficient to do full justice to the 3 Mc/s video bandwidth of the 405-line system where there are 490 picture elements per scanning line.

The equation derived for motion pictures in Part lea) is:

M = O' 32F+ 0"44H+ 0" 36J+0' 38K- O' 90 (4)

The correlation coefficient between the calculated values of M and the experimental values is O' 71. It will be observed that the same parameters appear in equation (4) as in equation (3), although with different coefficients. "Fideli ty of colour reproduction" (E) is still the most important single variable, "picture brightness" (K) is again second in importance but "misregistration" (F) is now the least important variable. This is probably due to the fact that registration errors are not so easily observed on a moving picture.

The statistical analysis of the results for slides in Part l(b) shows that no variables correlate significantly with the "overall assessment If. This means that such variations of opinion about the slides as exist are almost completely random and no single characteristic contributes significantly to the "overall assessment n. A possible conclusion to be drawn from this is that a good engineering balance has been achieved between the various parameters of the system in so far as slides are concerned; thus, in order to effect further improvement, equal attention must be given to each parameter.

The above conclusion does not, however, apply to 16 mm motion picture film. The equation derived from the individual results for motion pictures in Part l(b) is:

M = O· 34C +0- 22H +0' 48J +0' 24K - O' 29 (5)

The correlation coefficient existing between observed and calculated values of M is 0·74. The most notable feature of this equation is the fact that "fidelity of colour reproduction" (H) is no longer the most important variable. This is probably a tribute to the very good colour rendering of the particular film specially made for this test. "Colour trailing due to movement" (C) is a new variable and follows "picture sharpness" (J) in order of importance.

Correlation techniques have also been applied to the individual data for the reverse-compatible picture. The results of these analyses are given in Appendix VII.

6. TEST 3, PART 2 (THE "PROGRAMME" TESTS RADIATED FROM CRYSTAL PALACE)


The transmitting and viewing arrangements were the same as for Test 3, Parts l( a) and 1(b), (Section 5.1), but there were two additional sources of colour picture. One of these was the colour studio at Alexandra Palace which is equipped with two colour cameras: the other was the 35 mm film scanner, which was not available until 17th April. It was used, however, for almost all the film transmissions in Test 3, Part 2, on and after that date.

The emphasis for this set of transmissions was on programme interest. Thus, simple studio productions covering a wide range of programmes were transmitted with a change of programme at about three-weekly intervals. The productions included drama, ballet, variety, a mannequin parade and a demonstration of cookery. A short colour film was also included in each transmission and the programme started with one of the colour slides used in Test 3, Part 1( a). The questionnaire for these "programme" tests is shown in Appendix 11: it will be seen to be very similar to the questionnaire used for Tests 1, 2 and Test 3, Parts l(a) and l(b), with the difference that the questions on the reverse-compatible picture were omitted. transmitted colour pictures exclusively.

Test 3, Part 2,

The completed questionnaires received from viewers during the period 4th January to 17th May 1957 numbered 265. Questionnaires received during November and December 1956 have been omitted from the analysis because the results were regarded as unreliable on account of a number of diffi cul ties of a temporary nature. This is perhaps inevitable at the beginning of a new and complex technique. The improved results obtained in the present analysis, which covers the period when most of the temporary difficulties had been eliminated by positive action, appear to justify the exclusion of the earlier results.


The mean gradings for the various characteristics are shown in Table 11, which also includes histograms. Full details of the percentages of observers in each grade are given in Appendix VIII.

I'

r

28

TABLE 11

Results of Test 3, Part 2


CHARACTERISTIC Part 2

I Fi I m Camera Picture.:: SI ; de

A Visibi I ity of crawl ing dots 1·2 L 1·3 L 2·2 ~

B Colour synchronising difficulties 1·1 L 1·1 L 1·1 L C Colour trai I ing due to movement 1·3 L 1·5 L D Noise 1·11 L 1·8 L 1·11 L E Multiple image effects 1·2 L 1·3 L 1·2 L F Misregistration 1·8 Lh--. 2·6 ~ I·g ~

G Cross-co I DU r 1·1 L 1·1 L 1·6 L H Fidel ity of colour reproduction 2·3 ~ 2·5 ~ 2·0 ~ I Achromaticity of the grey scale

J Pi ctu re sharpn ess 2·1 ~ 2·5 tlL.... 2·0 ~ K Picture brightness I·g LL--- I·g LL---. I·g ~ L Contrast range 2·1 ~ 2·3 ~ 2·1 ~ M Overall assessment 2·1 LlL---. 2·5 ~ I·g L

6.2.1. Results for the Slide

The mean gradings for the various characteristics range from 1"1 to 2"2. It will thus be seen that all the characteristics are in the "very favourable" and "favourable" classes. This statement was also true for the slides in Test 3, Part 1(b). "Colour synchronising difficulties" (B), "noise" (D) and "multiple image effects" (E) are in the "very favourable" class of mean gradings. "Visibility of crawling dots" (A), "misregistration" (F), "cross-colour" (G), "fidelity of colour rendering" (H), "picture sharpness" (J), "picture brightness" (K), "contrast range" (L) and "overall assessment" (M) are all in the "favourable" class.

The slide was included in Test 3, Part 2, to serve as a standard of reference with respect to Test 3, Part 1. If the appropriate mean gradings are compared in Tables 9 and 11, most of the characteristics will be seen to have similar mean grading-so The exceptions are "visibility of crawling dots", which was more noticeable in Test 3, Part 2, "fidelity of colour reproduction ", which was better in Test 3,

L

29

Part 2, and "overall assessment", which was also better. These differences were not unexpected, since the particular slide chosen (the "teapot slide") had highly saturated colours which gave rise to more noticeable crawling dots than almost any other slide we have seen. On the other hand, it was also a slide which was relatively easy to reproduce and usually gave a pleasing picture, unless a receiver was considerably out of adjustment. This accounts for the improvement in "colour rendering" and "overall assessment" as compared with the results averaged for a series of slides. The general conclusion, however, is that the transmissions in Test 3, Part 2, were of the same standard as in Test 3, Part 1.

6.2.2. Results for Motion Pictures

Table 11 gives the mean gradings for motion pictures, combining the dataon both 35 mm and 16 mm film transmissions. The range of mean gradings is 1'1 to 2'3, all of which mean gradings are in the "favourable" or "very favourable" classes. "Visibility of crawling dots" (A), "colour synchronising difficulties" (B), "colour trailing due to movement" (C), "noise" (D), "multiple image effects" (E), and "cross-colour" (G) are all in the "very favourable" class. The remaining characteristics are in the "favourable" class.

It is most instructive to analyse the results for 16 mm film and for 35 mm film separately, and this has been done for characteristics D, F, H, J and M. The results are shown in Table 12.

TABLE 12

Test 3, Part 2

Mean Grading Characteristic

16 mm film 35 ImlJ film

D Noise l' 5 1'4 F Misregistration 1'9 1"7 H Fidelity of colour reproduction 2'8 1'9 J Picture sharpness 2'5 1'8 M Overall assessment 2'4 1'8

The mean grading of "noise" (D) has changed only slightly: this subjective result is confirmed by objective measurements on the 16 mm and 35 mm film scanners 4

which show them to be very similar in their signal-to"-noise ratios. There is no significant change in "misregistration" (Fl; the film gauge cannot alter misregistration in the colour receiver and there are no registration problems in the film scanners.

"Fideli ty of colour reproduction" (H) has improved by almost a grade for 35 mm as comp ared with 16 mm film s. This improvement is entirely due to the film stock, since the colour analysis characteristics of the two film scanners are very similar\ The 35 mm filmsused on and after 17th April were Eastmancolor stock on all occasions. The 16 mm films used in the earlier part of the test (i.e. before 17th Aprillwere duplicates of Kodachrome originals.

-'Picture sharpness" (J) improves by 0'7 of a grade on changing to the larger

gauge of film. The marked improvements in "'fidelity of colour reproduction" and "sharpness" result in an "overall assessment" (M) which is just over half a grade

better for 35 mm film.

Whilst the colour rendering of the 35 mm film is in the "favourable" class

that of the 16 mm colour film is in the "unacceptable" class with 13% of the observations in grades 4, 5 and 6. The mean grading of the South African travel film used in Test 3, Part lea), was also in the "unacceptable" class with a mean grading of 3"1, which grading shows that it was of lower standard than the 16 mm films shown in Test 3, Part 2, which had a mean grading of 2'8.

The questionnaire for the "programme" tests (Appendix 11) included a question

"Did you think that colour added interest to the programme? ". The answers to thi s question have been analysed into opinions about motion pictures and camera pictures. The result for motion pictures was that 89% of the observers said "yes" to the question, 1% said "no H and 10% were doubtful or gave no answer.

6.2.3. Results for Camera Pictures

Examination of Table 11 shows that the mean gradings for camera pictures range from 1~ 1 to 2' 6. In the livery favourable" class are the following characteristics~ "visibility of crawling dots" (A), "colour synchronising diffi,culties" (B),

"colour trailing due to movement" (C), "multiple image effects" (E), and "crosscolour" (G). The following characteristics are in the "favourable" class; "noise" (D), "colour rendering" (H), "picture sharpness" (J), "picture brif1htness" (KJ, "contrast range" (L), and "overall assessment" (M). "Misregistration" is in the "unacceptable" class with 17% of the observations in grades 4, 5 and 6.

Although"fidelity of colour reproduction"is in the "favourable" class it is on the boundary with a mean grading of 2-5 and leaves something to be desired if one takes into consideration the fact that 14% of the observations are in grades 4, 5 and 6 (Appendix VIII). Examination of the answers on this characteristic shows that there are considerable fluctuations and that on two occasions, 27th March and 3rd April, 40% of the observers used grades 4, 5 and 6~ this percentage was not approached on any other occasion on which a sufficient number of valid forms were returned to make an assessment significant.

"Fidelity of colour reproduction" is undoubtedly a difficult characteristic for observers to assess without being influenced by other factors. In any colour assessment where direct comp'arison between the original and the reproduction is not possible, an observer's opinion of ilfideli ty of colour reproduction" must be, to some extent, a guess and be strongly influenced by what he thinks the scene should look like. Although this is a perfectly valid criticism of the colour picture from the individual observer's point of view, he may well be criticising the work of the producer and set designer rather than the technical performance of the colour system. It may be significant that the same programme was radiated on both occasions referred to above on which an unusually unfavourable opinion was expressed. It consisted of a cookery demonstration in a modern highly-coloured kitchen which many people might consider to be quite unrealistic,

31

"Misregistration" (F) isthe most unfavourable characteristic of the pictures from the colour cameras and is in the Jiunacceptable" class. The studio camera is not alone responsible for the unfavourable grading, because with slides and films, where there is no registration problem at the transmitting end, the mean gradings are about 1'8 to 1"9. The registration of three separate images from the red, green and blue channels of the camera is a difficult technical problem and is sufficiently imperfect at the present state of the art, so that when this effect is added to the misregistration on the colour receiver an "unacceptable" grading is produced. As receivers improve, the combined error will be reduced. There is no doubt that technical progress will be made in attaining better registration in colour cameras.

"Picture sharpness!l (J) is on the boundary of the "favourable" class with a mean grading of 2' 5. Some improvement would be desirable as soon as it is technically possible. Nevertheless the present performance is certainly satisfactory.

In reply to the question LDid you think that colour added interest to the programme?" the analY,sis of the answers for camera pictures shows that 87i of the observers said 'yes", 3i said "no;! and the remainder were doubtful or gave no answer.

6.3. Correlation Techniques Applied to Test 3, Part 2

The statistical methods described in Sections 4.4 and 5.3 have also been applied to the results of Test 3, Part 2.

For the slide the equation derived from the partial correlation coefficients is:

M = 0"11F+0" 27H+0"10J + 0'05K+ 0"12L+ 0"7 (6)

This equation is not quite as successful in predicting the "overall assessment" as the previous ones, but nevertheless gives a correlation coefficient of 0"59 between the calculated value of M and the experimental value. Wi th over 250 questionnaires, the significance of such a correlation coefficient is well in excess of 1 in 1000*. The parameters which principally determine thebverall assessment" are, in order of importance, "fidelity of colour reproduction" (H), "contrast ratio" (L), "misregistration" (F), "picture sharpness 11 (J), and "picture brightness il (K). This equation cannot be directly compared with equation (3), Section 5.3, because the variable L was not significant for the slides in Test 3, Parts Ha) and Hb) (see Appendix Il. It is interesting, however, that whilst L has been added the influence of K has decreased substantially, the other parameters remaining unaltered. It is suspected that subjective impressions of brightness and contrast ratio are frequently confused by non-technical people, although in principle they should not be confused.

"Fideli ty of colour reproduction n is again the most important single parameter. The absolute values of the coefficients in equation (6) are less than those of equation (3), but their relative magnitudes are similar, particularly if the coefficients of K and L in equation (6) are added in order to compare with the coefficient of K in equation (3).

*The significsnee of a correlation lBoerficient 1s expressed as the probability that such a coefficient. could be achieved by ehaneec 1 in 1000 is usually considered as highly signlfi-cant8

32

For motion pictures (16 mm and 35 mm films taken together) the equation is:

(7 )

The correlation coefficient between the "overall assessment" calculated from this formula and the experimental values is 0'82. The parameters which mainly determine the "overall assessment" of film are, in order of importance, "fidelity of colour reproduction" CH), "picture sharpness" (J), and "contrast range" (L), "picture brightness" (K) and finally "misregistration!l (F!. Once again, "fidelity of colour reproduction" is by far the most important single variable. "Misregistration" now has very little effect on the "overall assessment''', partly because the subject material is moving and partly because the mean grading is "favourable!'. "Picture sharpness" and "contrast range" are equally important and next in order to "fidelity of colour reproduction" •

The equation for ca~era pictures is

(8)

This equation also succeeds quite well in calculating the "overall assessment" given the various individual gradings~ the correlation coefficient between the calculated and experimental values of M is 0'72. "Fidelity of colour reproduction (H) is still the most important item in the equation~ next in importance is "misregistration;; (F) followed by "picture sharpness ii (J), "contrast ratio! (L) and finally "noise" (DJ. It is interesting to note that .imisregistration", which had little importance in slides and almost none in films, now takes second place. This is in agreement with the known difficulties of securing good registration with a colour camera (see also Section 6.2.3). "Noise" appears as a significant parameter for the first time in Test 3. In this connection it is relevant to point out that, although the mean grading was 1'8, there were 13% of the observations in grades 4, 5 and 6. The histogram (Table 11) is definitely btmodal.

7. TEST 4 (MONOCHROME CONTROL EXPERIMENT)

7.1. Description of Test

During the period November 1956 to May 1957 the adapted N.T.S.C. colour television system had been subjected to a very searching and detailed examination. It appeared to be relevant to enquire what rating would be obtained if the present-day monochrome television service were subjected to the same kind of critical test. Accordingly, a new questionnaire was designed to see what assessment would be made of the pictures transmitted in the normal B.B.C. television service and received on a high-quality 21 in. commercial receiver. The questionnaire (Appendix IX) of necessity differs from the colour questionnaire, but it sets out to examine in full detail the known technical imperfections of monochrome television. The programmes chosen for this test were sporting events televised on 20th, 21st, 24th, and 25th June 1957. The test was conducted at Kingswood Warren (as was Test 1) and the observers were

allowed half an hour of normal programme in which to work through the questionnaire and give their assessments. A total of 79 observers was used, more than half of

-

whom were non-technical observers; most of the technical observers were not directly connected with work in television.

The conditions of viewing naturally have an effect on the assessments: for this test, the ambient lighting produced about ~ ft-L at the tube screen and peak-white on the television picture was about 20 ft-Le Observers were seated at distances of four times, six times and eight times the picture height. Some of those sitting at the nearest distance complained that it was too close for comfort able viewing, so that thi s distance was not used after the first two days.

These tests refer to only one of several types of television camera tube now in use in the B.B.C. The type used for all these outside broadcasts was the 4~ in. image orthicon (Mark In) camera channel.


Table 13 gives the mean gradings and histograms for the various characteristics. Full

details of the percentages of of observations in each grade are given in Appendix X.

The mean gradings will be seen from Table 13 to vary from lo2t0206. Three characteristics are in the "very favourable" class, viz., "transparency effect"*

A

B

C

D

E

F

G

H

I

J

K

L

H

N

0

p

Q

R

33

TABLE 13

Results of Test 4

CHARACTERISTIC MEAN GRADINGS AND HISTOGRAMS

Camera Pi ctu res

Visibi I ity of scanning lines 2·6 ~ Line strobing I·g ~

Vi si bi I i ty of moi re patterns 1·7 L Trai I ing due to movement 1·7 ~ Streaking 1·6 L Transparency effect 1·2 L Break-up of di agonal lines 2·0 l..LL-.

Geometrical distortion 2·0 ~

Noi se 2·6 ~

FI i eker 2·0 ~

Synehron i sing troubl es 1·2 L Redistribution effects 2·11 u.L.....

Hi erophony 1·2 L Sharpness 2·1 ~ Bri ghtness 1·8 L.L-.. Contrast range 2·2 ~

Tonal gradation 2·2 ~

Overall assessment of pictures 2·2 ~

(F), "synchronising troubles" (K) and "microphony" (M). Thirteen characteristics are in the "favourable" class, viz., "line strobing" (B), "visibility of moire patterns" (C), "trailing due to movement" (D), "streaking" (E), "break-up of diagonal lines" (G), "geometrical distortion" (H), "flicker" (J), "redistribution effects" (L),

*Thi s effect reI ates p rineip ally to photo conductive tUbes and is mo at not! cesbl e wben a dark object moves in front of a bright background: under these conditions the dark object tails to obscure the background and hence appears transparent to some extent.

\

34

"sharpness" (N), "brightness" {O j, "contrast range" (P j, "tonal gradation 11 (Q) and "overall assessment" {RJ. "Visibility of scanning lines" (A) is "acceptable" and "noise" (l) is "unacceptable" with 14% of the observations in grades 4, 5 and 6.

The transmissions on 21st, 22nd, 24th and 25th June were not all of th e same standard. Thus, the mean grading for the "overall assessment" (R) for the Ascot programme on 20th June was 1'6 for the observers seated at six times picture height. The day was bright and sunny and the pictures were undoubtedly of very good quality. On 24th June, however, the pictures from Wimbledon were noticeably below the normal standard, mainly because the weather was very dull. On that occasion, the mean grading for the "overall assessment" (R) was 3'0 with 15% of the observations in grade 4 (viewing distance again at six times picture height). In making any compari-sons between the results in Table 12 and those relating to camera pictures from a studio, it should be remembered that Table 12 gives the average results for four outside broadcasts, where lighting conditions were not under the control of the producer.

8. DI SCUSSION

The detailed results for all four tests have been given in Sections 3, 4, 5, 6 and 7, and each has been described separately with few comparisons relating the results of one test to those of another. It is of great interest to examine the results as a whole to see whether any trends can be discerned. In order to do this, certain of the more important characteristics will be compared.

8.1. Comparison of "Overall Assessment" of the Colour Pictures (M)

The most important characteristic of the colour pictures is the "overall assessment" (M in Tests 1, 2 and 3, R in the control, Test 4). Whilst the individual characteristics are very helpful in analysing why "favourable" or "unfavourable" judgements are made, the general reaction to the pictures is given by this characteri sti c alone.

TABLE 14

Mean Gradings of "Overall Assessment" (Still Pictures)

Slides

Test 1 Test 2 Test 3

B.B. C. Commercial Receiver Receiver

Part Ha) Part Hb) Part 2

2"4 2'2 2'9 2'5 2'3 1"9

In Table 14, all the information on mean gradings of the slides for the "overall assessment"has been collected together. From this it will be seen that, with the exception of Test 2, the mean gradings throughout the tests have been in the "favourable" class. The table also shows that the results have improved as the tests have proceeded. The reasons why the mean grading for Test 2 could be expected to be "unfavourable" have already been described in Section 4.1.

r 35

Summarising the results for slides, we can say that with 3 in. X 2i in. (76 x 57 mm) Ektachrome originals as the slide material the gradings have always been "favourable" and have shown some improvement as the tests have proceeded.

TABLE 15

Mean Gradings of "Overall Assessment 11 (Hoving Pictures)

Hotion Picture (Film) Camera PictureE

Test 1 Test 2 Test 3 Test 3 Test 4

B.B. C. Cornmerci al ~eceiver Receiver Part Ha) Part Hb) Part 2 Part 2

2'6 2'4 3'4 3'0 2" 1 2'1 2"5 2"2

The mean gradings for the "overall assessment" of motlon pictures and camera pictures have been collected together in Table 15. Dealing first with motion picture results, it will be seen that the gradings were initially "unfavourable" and remained so for a considerable time until the film material was changed. The dividing line in the table corresponding to this change is between Test 3, Part 1( a) and Test 3, Part l(b). There can be little doubt that the original choice of film was unfortunate; subsequent experience showed that a substantial improvement 'was obtained with better quality film (Section 5.2.11. The improvement of almost a whole grade when the new film was used is conclusive proof that the "unfavourable" gradings for motion pictures in the earlier parts of the tests 'were due to poor film and not to the colour television system. If further proof of the importance of film quality is desired, attention is directed to Table 12 (Section 6.2.2) which shows that the mean grading for the "overall assessment" of 35 mm motion pictures gives the figure of 1" 8, representing a further improvement of O' 3 of a grade comp ared with the new 16 mm film used in Test 3, Part l(b).

Summarising the results for motion pictures, it is clear that the quality of the television picture is directly dependent on the quality of the colour film: given good 16 mm colour film, entirely satisfactory results can be achieved and further noticeable improvement is obtained when 35 mm colour film is used.

The camera results (Table 15) show that a mean grading (2'5) on the boundary of the "favourable" class has been achieved in the first six months of experimental operation of a colour studio. The mean grading of the pictures from a selection of outside broadcasts taken from the present B.B.C. monochrome service is 2'2 which represents a "favourable" reaction. It is to be noted that this grading is only O' 3 of a grade better than that of the colour-camera pictures from the colour studio, but some allowance should be made for the fact that pictures from outside broadcasts were used in Test 4.

8.2. Comparison of Mean Gradings of "Fidelity of Colour Reproduction" (Hl

This characteristic is the most important feature of the colour pictures and proof of this is given by the results of statistical analysis as described in Sections

r 36

4.4, 5.3 and 6.3. Table 16 collates the mean gradings for slides and shows that, apart from the picture on the commercial receiver in Test 1, the "fidelity of colour reproduction" was "unacceptable" until the change of slides and film was made in Test 3, Part l(b). This characteristic is one which cannot be assessed with any certainty in the absence of a direct comparison with the original slide. N everth el es s, observers certainly appear to be in no doubt when the colour rendering is "rather poor" or "poor" (i. e. grades 4 and 5). The improvement noted in the colour rendering of slides on and after 1st April 1957, i.e. Test 3, Part l(b), cannot be ascribed solely to the change of material, but must have been in part the outcome of the improvements made to the colour receivers and the experience gained in operating them.

TABLE 16

Mean Gradings of "Fidelity of Colour Reproduction" (Still Pictures)

Slides


B.B. C. Commercial Receiver Receiver Part 1(a) Part l(b) Part 2

2"6 2"3 2"9 2"6 2"3 2"0

The mean gradings of "fidelity of colour reproduction" for motion pictures and camera pictures are shown in Table 17. The colour rendering of the motion pictures up to and including Test 3, Part Ha), was "unacceptable" largely on account of the film material. The colour rendering of the new film used in Test 3, Part Hb), showed a great improvement over the film used previously in the tests, and this accounts for the improvement of 0-9 of a grade between the result for Test 3, Part 1 (a). and that for Test 3, Part Hb).

TABLE 17

Mean Gradings of "Fidelity of Colour Reproduction" (Moving Pictures)

Motion Picture (Film) Camera Pictures

Test 1 Test 2 Test 3 Test 3

B.B.C. Commercial Receiver Receiver Part 1(a} Part l(b) Part 2 Part 2

3"1 2"8 3"5 3~ 1 2"2 2"3 2"5

The "favourable" mean grading of 2" 3 for motion pictures in Test 3, Part 2, is a combination of the results for both 16 mm and 35 mm films. The colour rendering of 16 mm colour film used for this test has a mean grading of 2-8, which is in the ilU1l.acceptable" class (13% of observations in grades 4, 5 and 6). The figure of 2- 3

-

37

for the combined results is "favourable'; because of the later use of 35 mm films, the results for which gave a mean grading of 1'9.

The "fidelity of colour reproduction" of the camera pictures gives a "favourable" mean grading of 2'5: specific comments about this have been made in Section 6.2.3.

To summarise, the "fidelity of colour reproduction" is satisfactory for slides and for specially selected 16 mm film. In general, however, the quality of 16 mm film would seem to be inadequate for colour television broadcasting. The 35 mm films used in the test have given "favourable" gradings which are definitely superior

to those of the original 16 mm film specially made for the second phase of the "scientific" tests [Test 3, Part l(b)]. The "fidelity of colour reproduction" of camera pictures from the colour studio is just within the "favourable" category, but some improvement would be desirable in view of the importance of this characteristic.

8.3. Comparison of Mean Gradings of "Achromaticity of the Grey Scale" (IJ

This characteristic gave rise to the most unfavourable gradings in the tests. As previously stated, the achievement of a good neutral scale by a colourreproducing system is very difficult, since precise balance of the red, green and blue signals is demanded at all levels of signal. Nevertheless, Table 18 shows that a "favourable" rating was achieved during the latter part of the tests.

TABLE 18

Mean Gradings of "Achromaticity of the Grey Scale" (Still Pictures)

Slides


B.B.C. Commercial

Receiver Receiver Part l( a) Part 1(b)

3'4 3~ 1 3'0 3'0 2'4

8.4. Comparison of Mean Gradi:ngs of "Picture Sharpness" (J)

This characteristic was shown by statistical analysis to have considerable influence on the "overall assessment" in several of the tests and it is of interest to compare the mean gradings. The results for slides have been collated in Table 19, which shows that the mean gradings throughout the tests have been in the "favourable" class and have gradually improved as the tests proceeded.

TABLE 19

Mean Gradings of JiPicture Sharpness" (Still Pictures)

Slides


B.B.C. Commercial 1(a) Part 1.(b; Part 2

Receiver Receiver Part

2'2 2'4 2"5 2'4 2'1 2'0

, 38

The results for moving pictures, including camera pictures, are shown in Table 20. The result for Test 4 is also included. Apart from Test 2, the mean gradings are all in the "acceptable" and "favourable" classes. The reproduction of 16 mm film has shown a slight improvement as between Test 1 and Test 3, Part Hb). The motion picture result for Test 3, Part 2, is again the combined result for the two film gauges; 16 mm film by itself gave a mean grading of 2'5 and 35 mm film a mean grading of l' 8.

TABLE 20

Mean Gradings of "Picture Sharpness" (Moving Pictures)


Test 1 Test 2 Tes11 3 Test 3 Test 4

B.B.C. Commercial Receiver Receiver Part H aJ Part Hb) Part 2 Part 2

2'3 2'2 2"9 2"6 2' 1 2"1 2" 5 2'1

The camera pictures from the colour studio are just in the "favourable" class. Some improvement would be desirable, as the general opinion about them is that they are somewhat soft as compared with those from monochrome cameras. The mean grading of 2'1 from the outside broadcasts (Test 4) supports this point.

"Picture sharpness 11 is influenced at the present stage of development by the performance of the display tube. It is relevant to enquire whether it would continue to be regarded as entirely satisfactory if tubes with better sharpness were available: would the adapted N.T.S.C. system then be found to be introducing some degradation? Laboratory experiments using a trinoscope5 consisting of three high-grade 17 in. catbod~ ray tubes have shown that it is quite difficult to perceive any loss of sharpness on changing from a 9 Mc/s RGB system to the 3 Mc/s adapted N.T.S.C. system. From this we can conclude that picture sharpness is not limited to any great extent by the form of coding used in this system of colour television.

8.5. Comparison of Mean Gradings of "Misregistration" (F)

"Misregistration" is a problem that is primarily associated with the camera and display tube and is not dependent on the transmission system used. For slides and film, there are no registration difficulties as far as the picture-originating equipment is concerned. With the present form of studio camera this is not so, and the colour picture derived from a colour camera contains the registration errors of both camera and display tube. These points are brought out in Tables 21 and 22,

from which it will be seen that the only result in the "unacceptable" category is the one for camera pictures. The results for both motion pictures and slides show the gradual improvement which has taken place while the tests have been in progress. In this case, there can be no doubt that the improvement is due to the better performance of the receivers.

cc;

-

39

TABLE 21

Mean Gradings of "Misregistration" (Still Pictures)

Slides


B.B. C. Commerci al

Receiver Receiver Part l(a) Part Hb J Part 2

2'4 2'2 2' 3 1'9 1'9 1'9

TABLE 22

Mean Gradings of "Misregistration" (Moving Pictures)



B.B.C. Commercial Receiver Receiver

Part 1( a) Part Hb) Part 2 Part 2

2'4 2>4 2"5 l'S l'S l'S 2"6

S.6. Other Features of the Colour Picture

"Contrast range" (1) is one that was originally "unacceptable", but became

"favourable il as the tests proceeded. Once again this is a feature that is mainly determined by the display tube (in conjunction with the lighting conditions) and is not a function of the system of transmission. The data on this characteristic have

been collated in Table 23.

TABLE 23

Mean Gradings of "Contrast Range"

Motion Camera Slides Pictures Pictures

Test 1 Test 2 Test 3 Test 3 Test 3 Test 4

B. B. C. Commercial Receiver Receiver

Part 1( al Part l(b) Part 2 Part 2 Part 2

2'7 2'7 2'3 2'6 2'2 2'1 2'1 2'3 2'2

"Noise" (D) varied considerably during the tests as will be seen from Tables 24 and 25. The fact that it gave rise to a numerically high mean grading in Test 2 was only to be expected in view of the number of sites where the field strength

40

was less than 200~V/m. Neglecting Test 2, most of the results for slides were in the category "very favourable" throughout the test, the one exception being Test 1, B.B.C. receiver. Referring now to Table 25, and again excluding Test 2, the results for motion pictures show that the improved film used for Test 3, Part l(b) and the film in Part 2 both gave mean gradings in the "very favourable" class. As regards camera pictures, the mean grading for the colour pictures, Test 3, Part 2, was in the "favourable" class (1'8), and the monochrome pictures used in Test 4, derived from the current television service, were 'aunacceptable" in this respect with a mean grading of 2'6 and 14% of observations in grades 4, 5 and 6.

TABLE 24

Mean Gradings of "Noise" (Still Pictures)

Slides


B.B. C. Commercial Receiver Receiver Part 1( a) Part l(b) Part 2

1'7 1"2 3@0 1"4 1"2 1'4

TABLE 25

Mean Gradings of "Noise" (Moving Pictures)

Motion Pictures Camera Pictures

Test 1 Test 2 Test 3 Test 3 Test 4

B.B. C. Commercial Receiver Receiver

Part Ha) Part l(b) Part 2 Part 2

2'7 1'8 3@6 2'7 1'2 1"4 1"8 2"6

Certain characteristics are directly influenced by the type of transmission used. Thus, the "visibility of crawling dots" (A), "colour synchronising difficulties" (B) and "cross-colour" (G) are directly dependent on the use of an N.T.S.C.type of signal in the present series of tests. It is, therefore, of great interest to note that the mean gradings for all these characteristics were always in either the "favourable" or "very favourable" classes throughout the tests, including Test 2, where a very wide range of receiving conditions was used. The data on these three characteristics have been assembled in Table 26, which deals with slides, and Table 27, which deals with moving pictures (film and camera).

8.7. The Reverse-Compatible Picture

It is desirable that a colour receiver shall be able to reproduce pictures from the existing monochrome television service with a satisfactory standard of picture quality. The "scientific" tests [i.e. Test 1, Test 2 and Test 3, Parts Ha)

---

41

TABLE 26

SLIDES

Mean Gradings


Characteri stic B.B.C. Commercial Receiver Receiver

Part l( a) Part Hb) Part 2

A Visibility of 1'9 1'3 2'2 1'8 1'3 2'2

crawling dots

B Colour synchronising 1'0 1'0 1'4 1'4 1'2 1"1

difficulties

G Cross-colour 1'6 1'4 2'2 1'7 1'3 1"6

TABLE 27

MOVING PI CTURES

Mean Gradings

Camera Motion Pictures Pictures

Characteristic Test 1 Test 2 Test 3 Test 3

B.B.C. Commercial Receiver Receiver Part 1( a) Part 1(b) Part 2 Part 2

A Visibility of 1'7 1'7 1'9 1'5 1~1 1'2 1'3

crawling dots

B Colour 1'0 1'0 1'0 1'2 1'0 1'1 1'1

synchroni sing difficul ties

G Cross-colour l' 5 1"3 2'2 1'6 l' 2 1'1 1'1

and l(b)]- investigated this aspect of colour reception and the results for each test have been described in Sections 3.2.2, 4.2.2 and 5.2.2. The data for "overall assessments" (Dj are collated in Tables 28 and 29. Table 29 includes the result for the "overall assessment" in Test 4, which serves as a standard of comparison. Inspection of the results for all the tests shows that, in general, the reverse-compatible picture was assigned mean gradings in the '"favourable and "acceptable" classes. The only exceptions to this are Test 2~ motion pictures, {where the "noise" of the picture for a number of sites of low field strength made the overall result "unacceptable") and Test 1, commercial receiver. As the results are satisfactory, a detailed analysis similar to that which was given for the colour picture in Sections 8.2 to 8.6 will not

42

TABLE 28

SLIDES

Mean Gradings of "Overall Assessment" of Reverse-Compatible Picture


B.B.C. Commercial Receiver Receiver Part l(a) Part 1(b)

2'2 2"8 2'4 2'5 2"2

TABLE m

MOTION PICTURES

Mean Gradings of "Overall Assessment" of Reverse-Compatible Picture


B.B.C. Commercial Receiver Receiver Part 1( a) Part Hb)

2"1 2'5 2"8 2"6 2"3 2"2

be given, It suffices to say that the picture is "favourable" in all the individual characteristics, N to T, with the single exception of "contrast range" (T) which was "unacceptable" in Test 3, Part 1( a), slides. Further, the results for Test 3 include commercial receivers as well as the one designed by the B.B.C. Research Department.

9. mNCLUSIONS

9.1. The Colour Picture

Extensive field trials have been carried out which involved the completion of over 500 questionnaires and extended over six months. Analysis of the results has shown that the colour pictures produced by the N. T. S. C. system as adapted to 405 lines, with the picture sources and display tubes that are at present available, are satisfactory. The detailed results quoted in this report show that although the colour pictures were marginal in their acceptability at the beginning of the tests (i.e. November and December 1956) the later results in all cases, except one, show "favourable 1l mean gradings, with only small percentages of observations in grades 4, 5 and 6. The one exception relates to "misregistration" arising from the colour camera where the result is "unacceptable" (Section 6.2.3). Those features that are specifically related to the method of coding adopted in the N.T.S.C. system show mean gradings which are at the worst "favourable" and in many cases are "very favourable", Certain features of the display tube could with advantage be improved (e.g. "picture sharpness", registration, "picture brightness") and the problem of registration with the threetube colour camera requires attention: nevertheless, at the present state of the art

r

IL

43

it would appear that the technical performance of the system is adequate for the launching of a colour-television service in the frequency bands at present in use.

A survey of the results of the "programme" tests radiated from the Crystal Palace transmitter shows that:

98% of the observers regarded the slide as satisfactory* 93% of the observers regarded 16 mm film as satisfactory 100% of the observers 'regarded 35 mm film as satisfactory 89% of the observers regarded the camera picture as satisfactory

(See Appendix VIII)

9.2. The Reverse-Compatible Picture

Although of secondary importance, it is nevertheless a very desirable property of a colour television receiver to be able to produce satisfactory reversecompatible pictures. Whilst the standard of monochrome pictures produced by a colour receiver is (with present-day colour displays) somewhat lower than that of a receiver designed for black-and-white transmissions, the detailed results given in this report show that the reverse-compatible picture is generally satisfactory. Summarising the results of Test 3, Part 1 (the "scientific" test radiated from the Crystal Palace transmitter) we have:

91% of the observers regarded the slides as satisfactory 91% of the observers regarded the 16 mm films as satisfactory

(See Appendix VI, results of Parts l(a) and l(b) combined).

10. ACKNOWLEDGH:MENTS

These tests, which formed a part of the Corporation's programme of work on colour television, were undertaken by the Designs and Research Departments in close co-operation with the Colour Television Sub-Committee of B.R.E.M.A.

11. REFERENCES

1. "Colour Television: The Adaptation of the N.T.S.C. System to U.K. Standards. Part 2: A Colour Television Film and Slide Scanner", B.B.C. Research Department Report No. T-060/2.

2. "Colour Television; The Adaptation of the N.T.S.C. System to U.K. Standards. Part 5: Some Problems Encountered in the Use of a Low-Power Transmitter", B.B.C. Research Department Report No. T-060/5.

3. "Colour Televi sion: The Adaptation of the N. T. S. C. System to U. K. Standards. Part 7: A Colour Receiver for System Appraisal", B.B.C. Research Department Report No. T-060/7 (to be issued shortly).

4. "A Compari son of the 16 mm and 35 mm Colour Film Scanners at Alexandra Palace", B.B.C. Research Department Technical Memorandum No. T.1023.

5. "Colour Television: The Adaptation of the N.T.S.C. System to U.K. Standards. Part 6: Display Systems", B.B.C •. Research Department, Report No. T-060/6.

*The interpretation of 'satisfactory' is that the rating is in grade 1, 2 or 3.

, ·

· ~ · · :;

" · " -

,

· · · ·

EXPERIMENTAL COLOUR PROGRAMME QUESTIONNAIRE

Ur:ad("r 12" 12"-16" t'll'lIr 16"

NlIIle ................................ .

Address ............................. .

Picture width in inches (measured) I I I I (et ate ea.et width but place in approprlet,e _quare)

Viewing distance (feet) .......................... .

Make of set ......................... . Line visibili(~Bea~c~~!So/is~~!~gldbie~~~ce c=J Model No ••••••••••••••••••••••••••••• Qual i ty of in(~e:.' ~~~" of ".,. 2 .. ,,.) r::::==J

Characteri stic I~~al e SI i de Numb..,.

~~t Any Comme" ts I u-sed: I 2 3 ~ IpjCtur"-"

A Visibil ity of crawling dots I

B Colour synchronising difficulties I

C Colour trail ing due to movement I

o No i se I

Multiplei~ ef~s I

_~sregistration (presence of colour fringes) I

G Cross-_co I a,,-,=- I

H Fidel ity -,,~Iour-'"!Produ~on 2

Achromaticity of the grey scale 2

~ Pi~tIJr"~ sharp-"ess 2 L Picture brightness 2

Contrast range 2

JM ov(~all as ssment of colour picture 2 including all the above effects)

IN Colour trai 1 ing due to movement I

~ Noi se I

ip Multiple~ eff~s I

It MisreJlJstration (pres,nce of colour fringes) I

IR Achromaticity of the picture l= Is Pi ctu re sh arpness

IT Contrast Range

Iu Ov' all ,t of the bl ack and wh i te picture-(includi-ng all the above effects)

Please keep to your stated viewing distance (except for observing resolution of Test Card "en)

tlek here

{

dark

Lighting conditions soft lighting

normal room 1 i ghting

Approx, distance from transmitter (miles) ••••••••••

Date of viewing ••••••••••••••••••••••••••••••••••••

Black and Vt11ite Resolution of Test Card "en

I 2 Mc/ s 12'5 Mc/ s 13'0 Mc/ si

(

Score 1-6 1 :: excellent) see se al e 2 belo.. 6:: ,.ery poor

etc.

Time taken to I ine up the set hours ......

Was the set readjusted during I::~r 'H, the transmission . _

I f so, state how many times •••••

Seal e I

impereepti bl e

just perceptible

defin i tely percepti bl e but not disturbing

somewhat objeetionabl e

defini tely objectionable

unusable

Score

Seal e 2 Score

excel I en t

good

fairly good

rather poor

poor

very poor or absent

~

5

EXPERIMENTAL COLOUR PROGRAMME QUESTIONNAIRE

UDder 12" 12"-16" O ... e .. 16"

Name •• 0 •••••••••••••••••••••• 0 •••••••

Address ............................. .

Picture width in inches (measured) I ! ! (lit ate exact width but place in appropriate square)

Viewing di stance (feet) ......................... ..

Make of set ........................ .. Line visibil i(?sea!C~~~sofvia~~!~gl dbie~!~ce c:=J Model No .... , ....................... . Quality of in(t;:.I~~~ .. of ,., .. 2 bot,.) c::::=J

$(";al e Film Came ra Characteristic to be SI i de Movi n9 Pi ctu res Any Comments used Pi ctu res

A Visibility of crawl ing dots I

B Colour synchronising difficulties I

C Colour trailing due to movement I IV'~ 0 Hoi se I

E Multiple image effects I

F Mi sregi stration (presence of colour fringes) I

G Cross-colour I

H Fidelity of colour reproduction 2

J Picture sharpness 2 K Picture brightness 2

L Contrast range 2

M Overall assessment of colour picture 2 (including all the above effects)

Di d you th ink that colour added interest to the programme?

Any other comments.

Please keep to your stated viewing distance (except for observing resolution of Test Card "C")

Please return the completed questionnai re to Head of Designs Department.

t.1ek here

{

dark


normal room 1 ighting

Approx. distance from transmitter (miles) ••••••••••

Date of viewing ••••••••••••••••••••••••••••••••• , ••

Black and White Resolution of Test Card "C"

12 Mcls 12'5 MC/S!3'Q Mclsl

(

Score 1-6 1 = ell.Cell",nt) see se a1", 2 b"'lo" 6 = Tery poor

et\).

Time taken to I ine up the set hours •••••. tiek here

Was the set readjusted during ~Noesl the transmi ssion ~_[:=--_=:J

I f so, state how many times ••••.

Scal e I

imperceptible

just percepti bl e

defin i tely percepti bl e but not disturbing

somewhat o1:ljeetionabl e

defini tely objectionable

unusable

Seal e

Score

Score

excellent ] good 2

fai rly good 3

rathee poor ~

poor 5

very poor or absent 6

46

A

B

C

D

E

F

G

H

I

J

K

L

M

N

0

P

Q

R

S

T

U

APPENDIX I II

Detailed Results of Test 1

PERCENTAGE OF OBSERVERS IN EACH GRADE FOR EACH CHARACTER I ST I C

BBC Rece i ver Commerc i al Receiver

CHARACTER I ST I C 16 mm fi Im SI ides 16 mm film SI ides

Grade Grade Grade Grade

I 2 3 ~ 5 6 I 2 3 ~ 5 6 I 2 3 ~ 5 6 I 2 3 ~ 5

Visibil ity of crawl ing dots 6~ 14 11 7 ~ 0 159 13 17 3 8 0 59 I~ 2~ 3 0 0 79 15 6 0 0

Co Iou r synchronising difficulties

Co 1 DU r trailing due to movement 61 26 9 4 0 0 / 1 1 1 V V 59 33 8 0 0 0 1 / 1 V V No i se . I~ 12~ 40 19 3 0 49 33 16 2 0 0 50 21 25 4 0 0 87 9 0 4 0

Multi pi e image effects

Mi sregi stration 19 38 2~ 19 0 0 23 39 19 17 2 0 21 31 3~ I~ 0 0 26 35 3~ 5 0

Cross ... co lour 62 25 13 0 0 0 61 20 16 3 0 0 72 21 7 0 0 0 73 17 3 6 I

Fidel ity of colour rep roduct i on 8 27 31 15 19 0 91 ~6 27 17 I 0 11 32 32 18 7 0 15 ~9 30 6 0

Achromaticity of the grey seal e 1 V V IV V V 0 28 32 16 24 0 / V 1 V I1 1 o 38 23 35 0

Picture sh arpn ess 14 50 25 1 11 0 0 14 !32 17 5 I 0 13 50 37 0 0 0 9 50 30 10 I

Picture brightness 2" ~6 18 7, 0 0 39 49 11 I 0 0 30 ~o 23 7 0 0 29 53 18 0 0

Contrast range V /IV V 1 / 15 22 ~8 11 ~ 0 11 V 1 V 11 IV 7 ~I 3~ 11 7 .. -

Overall assessment 8 35 1 ~2 IS 0 0 ~ 57 35 ~ 01 0 11 ~5 35 11 0 0 7 66 26 I 0

Co I ou r trailing due to moveJ'lierot 71 25 0 ~ 0 0 / 1 1 / 1 / 7~ 26 0 0 0 0 / / / V 1 No i se 32 50 18 0 0 0 66 22 6 5 I 0 73 2~ 3 0 0 0 77 19 I 3 0

Mu I tip le image effects

Misregistration 39 25 25 11 01 0 33 ~8 I~ ~ I 0 23 30 3~ 13 0 0 9 36 33 20 2

Achromaticity of the pi ctu re 26 3i 30 7 0' 0 25 37 29 6 3 0 10 52 24 I ~ 0 0 12 34 37 16 I

Pi ctu re sh arpn ess 24 ~5 31 0 0 0 15 55 23 7 0 0 7 62 28 3 0 0 2 38 45 14 I

Contrast range 1 / 11 1 V 1 18 39 32 11 0 0 / 1 1 11 11 l( 15 44 26 8 7

Overall assessment 18 5.3 25 4 0 01

13 6~ 14 9 0 0 3 53 37 7 0 0 2 31 53 13 I

The figures for 51 ides are the averages for SI ides 2,3 & If. except for characteristics I,l & T where the results are for Sl ide I only. No distribution is given for B,E & P because these effects were non-existent for Test I A nominal grading of 1'0 has been inserted in Table 3 for these characteristics.

""""lII!Il

6

0

1 0

0

0

0

~

0

0

0

0

11 0

0

0

0

0

0

-

A

B

C

D

E

F

G

H

I

J

K

L

M

N

0

P

0

R

S

T

U

APPENDIX IV


PERCENTAGE OF OBSERVERS IN EACH GRADE

FOR EACH CHARACTER I ST I C

CHARACTER I STI C 16 mm film SI ides

Grade Grade I 2 3 ~ 5 6 I 2 3 ~ 5 6

Visibility of crawling dots 27 60 12 I 0 0 21 ~~ 27 8 0 0

Colour synchroni sing difficul ties 99 I 0 0 0 0 91 2 0 0 0 7

Colour trai 1 ing due to movement 31 ~9 20 0 0 0 1 il 11 11 r7 [7 Noise 0 13 36 29 21 I 6 35 26 18

Mul tipl e image effects 37 36 16 10 I 0 38 38 20 ~

Mi sreg i strat i on 6 ~6 ~I 7 0 0 7 62 30 I

Cross-colour 17 ~7 33 3 0 0 23 ~O 31 6

Fidelity of colour reproduction 0 3 5~ 33 10 0 I ~3 29 23

Ach romat i city of the grey seal e / V 11 V / / 5 26 38 27

Picture sharpness 0 21 70 9 0 0 I 53 ~I 5

Picture brightness I~ 62 23 I 0 0 25 6~ 9 2

Contrast range / 1 / V V / 9 63 19 6

Overall assessment o 12 56 17 I~ I o 37 ~3 15

Co Iou r trai 1 ing due to movement 55 29 16 0 0 0 I / / / Noise I ~7 29 13 10 0 9 ~7 28 8

Multiple image effects ~2 36 I~ 8 0 0 39 ~O 16 5

Misregistration 5 ~2 ~3 10 0 0 12 59 26 3

Achromaticity of the picture 21 53 21 5 0 0 2~ 60 15 I

Picture sharpness I 36 56 7 0 0 ~ 60 32 ~

Contrast range 11 11 11 V 11 11 17 67 10 3

Overall assessment o 37 ~7 11 5 0 I 62 28 8

The figures for slides are the averages for Slides 2,3 & ~ except for characteri st i cs I, L & T where the resul ts are for SI i de I on I y.

15 0

0 0

0 0

0 0

3 I

~ 0

0 0

0 0

3 0

~ I

/ 7 8 0

0 0

0 0

0 0

0 0

3 0

I 0

47

r 48

APPENDIX V

Details of Sites for Test 2

Open Field Site N.G. Map Distance Circuit Strength No. Location

Reference from K. W. Remarks Volts at at 22 ft Receiver AGL

Miles km mV mV/m

1 Wal ton Heath 234552 0-875 1-4 Open ground - some trees. 4'00 2"51 75 yd from main road.

2 Wal ton Heath 222536 2"125 3"4 Private road-very little 3'2 2·00 traffic. Open towards transmi tter.

3 Banstead- 250603 2"75 4"4 Shallow valley with some 2"28 1"41 Cross Roads trees. 100 yd from

main road.

4 Headley 204537 3 4"8 Open site. 75 yd from 1'6 1'00 Heath main road. No trees.

5 Holmwood 175452 8 12'8 Minor road - surrounded 0"11 0"07 by trees. Little traffic.

6 Ranmore 127503 8-25 13'2 Car park. Open towards 0'22 0'14 Common transmi tter. 100 yd from

main road.

7 Wal ton Downs 227574 1" 5 2"4 Minor road- some houses. 1'46 0'89 100 yd from main road. 20 yd from railway bridge.

8 Chipstead 268585 2 3"2 Rough track on open 1'78 1'12 Valley ground. 75 yd from

minor road.

9 Chipstead 266583 1'75 2"8 Farmyard- trees towards 0'45 0"28 Valley transmi tter. 100 yd from

main road.

10 Box Hill 184514 4'75 7'6 Minor road- surrounded 0-11 0'07 by trees. Little traffic.

11 Epsom Downs 225578 1-75 2"8 Car park- open site. 3"55 2'23 50 yd from main road. Moderate traffic.

J

49

Open Field Site N.G. Map Distance Circuit Strength No. Location

Reference from K. W. Remarks

Vol ts at at 22 ft Receiver AGL

Miles km mV mV/m

12 Reigate 23'7501 3'75 6"0 Minor road- some trees 0-18 0' 11 Heath but open towards trans-

mi tter. Moderate traffic.

13 Ep som Common 197608 4-5 7-2 25 yd from minor road. 0'28 0'18 Some houses. Broken-down car nearby providing most of ignition interference.

14 Tolworth 199658 6'75 10'8 On main road. Few 0'20 0'12 Station houses. Considerable

traffic.

15 Box Hill 187513 4'5 7'2 Minor road. Some houses. 0'28 0'17 Li ttle traffic.

16 Headley 205542 2'75 4'4 Open site on minor road. 0'5 0'4 Li ttle traffic.

17 Epsom Car 206607 4'0 6'4 Built-up. Car park with 0'18 0'11 Park several cars. 50 yd from

main road.

18 Woodman- 289599 3'75 6"0 Built-up minor road. 2'0 1" 26 sterne Very little traffic.

19 Reigate Hill 263523 2'5 4"0 Car park on minor road. 3-82 2'24 Some traffic. Site surrounded by trees.

20 Belmont 257619 3'75 6-0 Open car park. Moderate 0-5 0'32 traffic

21 Epsom Golf 224589 2'5 4"0 Open car park. 0'79 0'5 Course Very little traffic.

22 Headley 207531 3'0 4'8 Minor road. Surrounded 0'89 0'56 Grove by trees. Some traffic.

23 Gatton 265527 2'25 3'6 Minor road. Some traffic. 1'0 0'63 Bottom Site surrounded by trees.

24 Gatton 268528 2'25 3'6 Minor road. Some traffic. 0'5 0'32 Bottom Site surrounded by trees.

25 Lower 244532 1'75 2'8 Quiet road. Some houses. 1-0 0'63 Kingswood Li ttle traffic.

---

11

" )1

d 11 li I,

!f

50

<r => o ...J o <>

A

B

C

D

E

F

G

H

I

J

K

L

M

N

0

P

Q

R

5

T

U

APPENDIX VI

Detailed Results of Test 3, Parts lea) and l(b)

PERCENTAGE OF OBSERVERS IN EACH GRADE FOR EACH CHARACTER I ST I C

Part I (a) Part I (b)

CHARACTERiSTIC 16 mm fi Im I SI ides 16 mm fi Im SI ides

Grade

I Grade Grade Grade

I 2 3 ~ 5 6 I 2 3 ~ 5 6 I 2 3 ~ 5 6 I 2 3 ~

Vis i b i I i ty of crawl in g dots 70 21 5 2 0 2 5~ 2~ 13 8 I 0 9~ 6 0 0 0 0 67 33 0 0

Co Iou r synchronising difficulties 91 6 I 2 0 0 81 9 ~ 3 I 2 97 3 0 0 0 0 87 13 0 0

Colour trailing due to movement 71 19 9 0 I 0 / / 1/ 1/ 1/ 1 8~ 10 6 0 0 0 1/ / I1 V No i se 28 16 27 23 6 0 76 18 6 0 0 0 8~ 10 6 0 0 0 77 23 0 0

Mul ti pie image effects 85 11 ~ 0 0 0 85 11 3 I 0 0 87 13 0 0 0 0 87 10 3 0

Mi sreg i strat i on ~I ~~ 11 ~ 0 0 38 ~O 18 3 I 0 3~ 50 13 3 0 0 30 60 10 0

Cross-colour 69 16 11 ~ 0 0 59 20 12 8 I 0 75 25 0 0 0 0 7~ 23 3 0

Fidel ity of colour rep roduct i on 7 16 ~5 25 6 I 10 ~2 33 12 3 0 13 56 28 3 0 0 7 63 23 7

Ach romat i city of the grey scal e V 1 1 V / / 7 2~ 38 28 3 0 11 / 1 / 1 V I~ 38 ~3 5

Picture sharpness 11 ~O ~O 8 0 I 121~~ 36 7 0 I 16 53 28 3 0 0 7 73 17 3

Picture bri ghtness 15 53 26 6 0 0 20 52 2~ ~ 0 0 15 72 10 3 0 0 23 6~ 13 0

Contrast range / / V V / / 8 39 35 13 5 0 11 / / / / 1 ~ 78 11 7

Overall assessment 6 16 52 21 5 0 8 ~o ~2 7 2 I 16 62 16 6 0 0 3 70 23 3

Co Iou r trai 1 i ng due to movement 73 20 6 I 0 0 V / V 1/ 1/ 1/ 80 10 0 7 3 0 I1 V V 11 No i se 52 31 I~ 2 I 0 82 13 ~ I 0 0 9~ 3 3 0 0 0 93 7 0 0

Multiple image effects 85 12 3 0 0 0 8~ 12 3 I 0 0 83 17 0 0 0 0 90 7 3 0

Misregistration 36 ~O 22 2 0 0 36 ~I 19 3 I 0 27 ~7 23 3 0 0 30 50 20 0

Achromaticity of the picture 27 ~3 21 8 I 0 21 ~5 23 8 3 0 27 53 20 0 0 0 17 70 10 3

Picture sharpness 12 ~8 33 5 2 0 13 ~7 29 10 I 0 27 ~o 33 0 0 0 10 70 20 0

Contrast range / V 1/ if V 1/ 11 ~o 33 12 ~ 0 I1 / 1 / 1 V I ~ 36 ~5 5

Overall assessment 9 35 ~6 8 2 0 8 ~3 38 7 4 0 13 50 30 7 0 0 3 74 20 3

The figures for 51 ides are the average for SI ide 2, 3 & ~ except for characteristics I, L & T where the results are for SI ide I only.

""

5 6

0 0

0 0

1 V 0 0

0 0

0 0

0 0

0 0

0 0

0 0

0 0

0 0

0 0

/ 1 0 0

0 0

0 0

0 0

0 0

0 0

0 0

51

APPENDIX VII

Application of Statistical Analysis to Results on Reverse-Compatible Pictures in Test 3, Parts H aJ and Hb J

The application of statistical analysis to the results for slides in Test 3, Part l(a), gives rise to the equation:

u = 0'380+0'36~HO'48R+0'49S-0'87 (9)

where U = grading of "overall assessment" 0= grading of "noise" Q= grading of Hmi sregistration" R= grading of "achromatici ty" S= grading of "sharpness"

This equation gives values of U calculated from the individual characteristics, which correlate with the experimental values with a correlation coefficient of 0'77. The variables in order of importance are, "sharpness" (S), "achromaticity" (R), "noise" (0) and iimisregistration" (Q). These agree with known defects of the reversecompatible picture, with the exception of "noise", the presence of which in equation (9) seems to be somewhat anomalous.

The equation for slides in Part Hb) is:

(10)

This equation gives a correlation coefficient of 0-79 when the calculated values of U are compared with the observed values. The equation for Part l(b) is simpler than the corresponding one for Part l(a) [equation (9)]- and it will be observed that the two remaining variables (;isharpness" and "achromaticity") are the two most important variables in Part Hal.

The equations for motion pictures for Parts l(al and l(b) are given in equations (11) and (12) respectively.

( 11)

U = 0' 12N +0' 45R +0' 38S +0' 5 ( 12)

The correlation coefficient between observed and calculated values of U for equation (11) is 0'79 and for equation (12) is 0'74. "Sharpness" (S) and "achromatici ty" (R) feature in both equations, although in reversed order of importance; there is the added variable, "colour trailing due to movement" (N), in equation (12), which slightly influences the results. The corresponding variable (C) for the colour picture was also present in the analysis of the motion picture results for Test 3, Part l(b) [see equation (5), Section 5.3] •

The relative importance of the various coefficients in equations (9) to (12) have been evaluated by-normalising the coefficients of each equation and the results are given in Table 30.

52

TABLE 30

Test 3, Parts lea) and lIb)

Relative Importance

Characteristic Motion Picture Slides

Part 1( a) Part 1(b) Part 1( a) Part 1(b)

0 Noise - - 22% -Q Misregistration - - 21% -R Achromaticity 25% 47% 28% 46% S Sharpness 75% 40% 29% 54% N Colour trailing - 13% - -

53

APPENDIX VIII

Detailed Results of Test 3, Part 2

PERCENTAGE OF OSSERVERg I N EA~H GRAnE

FO" tACH CHARACTER I ST I C

PART 2

~HAP.ACTER I ST I C '""i lm (16 & 35 mm) Carr,era Pictures SI ides

Grade Grade Grade

I 2 3 q 5 6 I 2 3 4 5 6 I 2 3 q 5 6

A Visibil ity of crawl ing dots 83 13 q 0 0 0 81 12 6 I 0 0 40 18 33 6 2 0

L Co Iou r synchronising difficulties 93 5 2 0 0 0 91 6 2 I 0 0 93 q 3 0 0 0

C Co Iou r trai 1 ing due to movement 76 18 5 I 0 0 59 29 10 2 0 0 / 11 11 11 11 1/ D No i se 67 24 7 2 0 0 58 13 16 12 I 0 63 30 7 0 0 0

E Multiple image effects 86 11 3 0 0 0 75 15 7 3 0 0 88 10 2 0 0 0

F t--1isregistration 39 42 16 3 0 0 22 27 34 15 2 0 32 51 14 3 0 0

G Cross-co 1 ou r 86 13 I 0 0 0 85 12 2 I 0 0 ~> 20 7 3 I 0

H Fidel ity of colour reproduction 22 42i 27 6 3 0 13 41 32 12 2 0 '26 57 13 2 2 0

J Picture sharpness 24 1\5127 4 0 0 12 37 42 8 I 0 25 51 22 2 0 0

K Picture brightness 31 52 1 16 I 0 0 29 50 17 4 0 0 31 58 10 I 0 0

L Contrast range 21 49 25 4 I 0 16 40 38 5 I 0 22 52 25 I 0 0

M Overall assessment 22 47 27 3 I 0 9 q3 37 10 I 0 21 65 12 I I 0

16 mm f i I m 35 mm film

D Ho i se 62 27 8 3 0 0 76 19 4 I 0 0

F Misregistration 39 39 17 q I 0 43 q2 15 0 0 0

H Fidel ity of colour rep roduct i on 16 35 36 9 4 0 30 53 15 2 0 0

J Picture sharpness 20 40 33 6 I 0 34 50 16 0 0 0

I! Overall assessment Iq 44 35 5 2 0 33 52 15 0 0 0

MONOCHROME TELEVISION APPRAISAL

Progrcunme ••••••••• ' •••••••••••••••••••••••••

Time

Date

{

dark


Characteristic

A Visibility of scanning lines

B Line strobing

C Visibil ity of moire patterns

D Trai I ing due to movement

E Streak ing

F Transparency effect

G Break-up of diagonal lines

H Geometri cal d i storti on

I Noise

J FI i cker

K Synchronising trou bl es

L Redistribution effects

M Microphony

N Sh arpness

0 Bri ghtness

P Contrast range

Q Tonal gradation

R Overall assessment of pictures (including all the above effects)

normal lighting

Scale to be Score used

I

I

I

I

I

I

I

I

I

I

I

I

I

2

2

2

2

tick here

Any Comments

-

Name •••••••••••••••••••••••••••••••

Make of set ...................... ..

Width of picture (inches) ••••••••••

Viewing distance (feet) ••••••••••••

Approx. distance from transmitter •••••••• # •••••

Scale I Score

impercepti bl e I

just perceptible 2

definitely perceptible but not di sturbing 3

somewhat objectionable ~ 1---

defin i tely objectionable 5 --unusable 6

Scale 2 Score

excel I ent I

good 2

fai rly good 3

rather poor ~

poor 5

very poor or absent 6

BE

APPENDIX X


PERCENTAGE OF OBSERVERS

IN EACH GRADE FOR EACH

CHARACTER I STI C CHARACTER I STI C

Grade I 2 3 ~ 5 6

A Visibil ity of scanning 1 ines 10 27 56 6 0 0

B Line strobing ~I 37 18 3 I 0

C Visibil ity of moire patterns 61 17 17 5 0 0

0 Trai I ing due to movement 5~ 29 13 ~ 0 0

E Streaking 61 2~ 12 3 0 ()

F T r an sp aren cy effect 82 12 5 I 0 0

G Break-up of diagonal 1 ines ~O 29 22 9 0 0

H Geometrical distort i on ~2 22 28 7 I 0

I No i se 12 3~ ~O I~ 0 0

J FI i cker ~5 25 17 11 2 0

K Synchronising troubles 83 11 3 I I 0

L Redistribution effects 26 25 38 9 2 0

M M i crophony B9 6 ~ I 0 0

N Sharpness 19 55 19 7 0 0

0 Brightness 38 ~9 11 2 0 0

P Contrast range 20 ~8 25 7 0 0

Q Tonal gradation 18 51 27 2 2 0

R Overall assessmen t 11 57 28 ~ 0 0

MM

Documents

COLOUR TELEVISION APPRAISAL 1956/57 FIELD TRIALSdownloads.bbc.co.uk/rd/pubs/reports/1957-31.pdf · Title SCDPE AND PDRPOSE OF THE TESTS THE QUESTIONNAIRE AND THE SYSTEM OF GRADING