Screen selection-for-digital-cinema (1)

Screen Selection for Digital 2D & 3D Cinema

Andrew RobinsonManaging DirectorHarkness Screens

ICTA June 2009Amsterdam

This presentation will cover the following topics:

• Brightness standards for digital cinema.• Differences between digital and 35mm projection. • Screen selection for digital projection.• Use of “gain” screens.• Digital 3D – screen implications. • Mixed digital 2D/3D applications.

Standards for screen luminance

SMPTE luminance standard for digital cinema is:• 14 fl in screen centre +/- 3fl.• 75% of centre brightness at the sides, minimum

9 fl. SMPTE 431-1-2006.• Luminance standard for 35mm projection is 16 fl.

Differences between digital and 35mm projection

• Digital projectors use short arc, high-pressure Xenon lamps which are more costly than 35mm Xenons.

• Light distribution from digital projector is more even than 35mm.

• Setting up and changing film formats on digital projectors can result in significant reduction of available light.

Digital Cinema Projectors

• Light outputs of up to 30,000 lumens are quoted by projector manufacturers.

• Achieving maximum lumens requires optimum set-up and operating conditions: - this may be costly in terms of operating costs

- in reality, incident light on screen may be significantly less

• Screen selection is important to achieve recommended light levels and to moderate operating costs.

Screen light efficiency

• Screens cannot create light; but they can optimise the reflection of it.

• Reflectivity of a screen is measurable and is usually called “gain”

• Gain is measured by comparing reflectivity of the screen with a reference standard and is expressed as a factor (e.g. 0.8 or 1.2).

• There is a British Standard for gain measurement (BS 5550), which uses a reference standard to compare screen materials.

• There are other measurement standards, but the BS is widely recognised and is used by Harkness to classify screen gain.

• This enables screen materials to be compared in the laboratory.

Measurement of gain

Projector

Light meter

Magnesium carbonate block

Screen surface

Gain is measured according to British Standard BS 5550

Types of cinema screen

Screens are available with various gain levels:• matt white: 'gain' typically 0.8 – 1.0• 'gain' screens: up to 2.0 or more

: typically mid gain (~1.4)

: or high gain (~1.8)

: above 1.8 gain there is a risk

of 'hot spotting'

Light reflectance

Gain screens reflect more light back to the audience than matt white screens

Gain Screen Matt White Screen

Measurement of viewing angle

Gain is measured at intervals of 10° by comparison with reference standard

Gain vs. viewing angle

•with all screens, perceived brightness reduces as viewing angle increases

•brightness of gain screens reduces more than matt white as viewing angle increases

Gain curves of typical screens

Picture formats / masking

2 most common movie formats are:• Cinemascope 2.35:1• Flat 1.85:1

Screen size can be adjusted by• keeping screen height constant• largest picture is ‘scope’

or

• keeping screen width constant• largest picture is ‘flat’

1

1

2.35

1.85

2k digital projectors : film formats

Native ‘scope’ screen

•The full resolution of the DMD is 1080 x 2048.

•Changing film formats with “constant height” can be done electronically by reducing the area of DMD that is used.

•Up to 37% loss of available light. Using motorised lenses reduces this significantly.


• alternatively using an anamorphic lens for ‘scope’ picture

•this maximises the use of available light – 10% light loss from lens

•requires activation of anamorphic lens

•these anamorphic lenses are expensive

•this is the only practical approach on large cinemascope screens


Native ‘flat’ screen

•Changing film formats on ‘constant width’ screens.

•This is easily achieved electronically.

•With digital projection, light is reduced changing from 1.85 screen to 2.35 screen, but so is the screen size. Brightness levels are maintained. (This is an advantage over 35mm when the opposite happens).

Xenon lamp light losses

• Digital projectors use high performance Xenon lamps.

• Usually more expensive, and have shorter warranty lives than 35mm lamps.

• Light loss at warranty life can be up to 40%.• Running beyond warranty life further reduces light.

Screen light levels

• Light losses from set-up and life-point of lamp can be as much as 50% of theoretical maximum.

• Screen gain level can make a big difference to screen brightness or lumens required.

• Medium to high gain screens (1.4 to 1.8) will reduce lamp power needs and can significantly reduce operating costs.

Screen light levelsLumens required to achieve 14 ft lamberts

Screen gain Screen width (m) / cinemascope format

12 15 18 22 30

1.0

1.4

1.8

2.2

9200 14400 20800 31000 57700

6600 10300 14800 22200 41200

5100 8000 11500 17200 32100

4200 6600 4400 14100 26200

The above lumens are for incident light on the screen (after losses).

Screen light levels cont’dLumens required to achieve 14 ft lamberts

Screen gain Screen width (m) / flat format

12 15 18 22

1.0

1.4

1.8

2.2

11700 18300 26400 39400

8400 13100 18800 28200

6500 10200 14700 21900

5300 8300 12000 17900

The above lumens are for incident light on the screen (after losses).

2k digital projectors : film formats• Optimum aspect ratio for digital projection is 1.90:1 (2048:1080).• If movies were made in this format and cinema screens were

this format, there would be significant benefits with digital projection– use all the DMD (no set-up losses)

– use all the available screen

– no need for anamorphic lens

– no “blockbusters” on a smaller screen

– no need for moving masking

• Many modern US theatres have “constant width” screens 1.85:1 which is very close to 1.90:1; less common in Europe

• Could 1.90:1 become a new standard?

Operating Savings

Based on 4000 hours annual use.

Examples of operating cost savings € p.a.

Using 2 kw instead of 3 kw lamp : 1940

Using 3 kw instead of 4 kw lamp : 4625

Using 4.5 kw instead of 6 kw lamp: 6300

1.8 gain screen costs including install €

11m flat 4000

14m scope 5000

18m scope 7000

There may also be initial investment savings if a smaller model projector can be used by reducing required lamp power.

Lamps

kw

user

price

€

warranty

life (hrs)

lamps lamp cost

p.a. € p.a.

power

cost

€ p.a.

operating cost

€ p.a. € per hr

2

3

4

4.5

6

800

1000

1250

1200

1500

2400

1400

700

1000

600

1.7 1360

2.9 2900

5.7 7125

4.0 4800

6.7 10500

800

1200

1600

1800

2400

2160

4100

8725

6600

12900

0.54

1.03

2.18

1.65

3.23

Practical Implications

• New installations of digital projectors- consider projector / lamp options together with screen gain

level- potential operating cost savings- capital cost savings if can use smaller projector

• Existing installations of digital projectors- by changing to high gain screens, may be able to reduce

lamp size and operating costs

Measuring screen gain in existing theatres

• Relatively easy to do this using light meter and reference card.

• Gain = L1 / L2 • Worthwhile also to measure absolute light levels in foot

lamberts.

Gain screens and viewing angles

Perlux 140 (1.4 gain)

half-gain angle = 50° (0.7 gain)

0° 10° 20° 30° 40° 50° 60°

0.00.2

View Angle

Gai

n

0.40.60.81.01.21.41.61.82.02.22.42.6

5°

PERLUX 140

Gain screens and viewing angles cont’d

Perlux 180 (1.8 gain)

half-gain angle = 34° (0.9 gain)

0° 10° 20° 30° 40° 50° 60°

0.00.2

View Angle

Gai

n

0.40.60.81.01.21.41.61.82.02.22.42.6

5°

PERLUX 180

•In this typical theatre almost all seats have better than half-gain level even with 1.8 gain screens.

Viewing Angle

Screen shape

A curved gain screen reflects more light back to the audience

Screen shape

•Gain screen curvature

Harkness guideline is 5% curve

R.O.C. = 5% of chord

20m screen width

1m screen depth

3D Cinema

• Stereoscopic 3D is growing fast, particularly in US.• Over 2,500 3D screens operational worldwide end

2008.• Forecast of 6,000 3D screens by end 2009 and 9,000

by end 2010.• 17 3D titles releasing in 2009; more in 2010/11.• Single digital projector gives economic 3D

performance.• High quality of digital 3D images.

3D Cinema Technologies

There are 3 main technologies used in digital 3D cinema:

• Polarised light systems– polarising filter / silver screen / passive eyewear

– e.g. Real D, Master Image, Imax

• Colour filters– colour filter wheel / white screen / passive eyewear

– e.g. Dolby

• “Active” eyewear– white screen / electronic “shutters” in eyewear

– e.g. Xpand

efficiency

Real D 15%

Real D XL 28%

Dolby 12%

Xpand 18%

3D Cinema light efficiency

“Acceptable” screen brightness level 4.5 fl. (14 fl. 2D)

All 3D systems absorb a large amount of light compared with 2D mode because of filters and eyewear

Screen implications for 3D Cinema

Polarised light systems (e.g. Real D)• Screen must maintain polarisation on reflection.• “Silver” screens (aluminium flake coatings).• >130:1 signal:noise ratio to maintain quality 3D

images.• Silver screens are intrinsically high gain (typically

2.4).• Compensates light losses from 3D.• Screens up to 14m with a single projector (22m with

Real D ‘XL’ system is possible).


Colour filter wheels (e.g. Dolby 3D) • Use white screens (do not need to maintain light

polarisation).• Gain screens required to overcome light loss

- up to 2.2 (maximum gain available)

• Up to 14m wide screen possible with single projector / 2.2 gain screen.


Active eyewear (e.g. Xpand) • White screen.• Gain screen needed for larger screens.• Screen up to 15m with single projector / 2.2 gain

screen.

Mixed 2D / 3D applications

• Acceptable brightness level with 3D is 4.5 fl – efficiency level 15%

• Recommended brightness level for 2D is 14 fl• Switching 2D / 3D modes

– 2D image too bright– change lamp / reduce power in 2D mode– Real D ‘XL’ system 2D / 3D modes in balance

• Increased risk of visible defects due to high gain• All Harkness 3D screens will support 2D content

– useful for mixed programming

Theatre shape

• 3D systems use high gain screens.• High gain screens have reduced viewing angles:

– Spectral 240 half-gain angle 24º– Perlux 220 half-gain angle 25º

• Best to use theatres for 3D which are long relative to width– throw minimum 1.5 x screen width

• With 3D, curving the screen is strongly recommended.

•This theatre has most seats with an acceptable viewing experience.

•Seats outside the half-gain angle will have an inferior viewing experience.

Viewing Angle

Summary

• For digital projection, it is recommended to use gain screens.

• Benefits in power use/lamp life can give big operating cost savings.

• Screen must be consistent with 3D technology chosen.

• For 3D digital screens, it is usually necessary to change the screen for the highest possible gain.

Technology

Screen selection-for-digital-cinema (1)