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Walter et al. Vol. 26, No. 10 /October 2009 /J. Opt. Soc. Am. A 2219

Objective approach for measuring changes incolor discrimination caused by transparent

colored filter media

Annette Walter,1,2,* Michael Schuerer,1 Timo Eppig,1,3 Achim Langenbucher,1,2,3 and Holger Bruenner1

1Medical Optics Research Group, Institute of Medical Physics at the University of Erlangen-Nuremberg,Henkestrasse 91, 91052 Erlangen, Germany

2School in Advanced Optical Technologies, University of Erlangen-Nuremberg, Paul-Gordan-Strasse 6,91052 Erlangen, Germany

3International Max-Planck Research School for Optics and Imaging, Guenther-Scharowsky-Strasse 1, Bldg. 24,91056 Erlangen, Germany

*Corresponding author: annette.walter@imp.uni-erlangen.de

Received April 23, 2009; revised August 7, 2009; accepted August 9, 2009;posted August 14, 2009 (Doc. ID 110461); published September 25, 2009

A novel measurement setup for determining the change in color perception due to laser protection filters isdescribed. The developed system overcomes color space limitations common to thin-film transistor displays byusing a LED illumination system, creating a large gamut covering a wide range of human color perception, andallowing adjustment of the respective spectra. An objective color matching method is used that is based on thework of MacAdam [J. Opt. Soc. Am. A 32, 247 (1942)] and enhanced by employing discrimination ellipses fittedon color discrimination thresholds on axes in the CIE 1976 USC chromaticity diagram. We present severalmeasured color discrimination ellipses with and without laser protection filters. © 2009 Optical Society ofAmerica

OCIS codes: 330.1720, 170.4460.

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. INTRODUCTIONepending on the chromatic properties of transparent fil-

er media, visual perception can undergo a shift in colornd a change in color discrimination when a person isooking through optical filter media, such as sunglasses orther tinted eyewear. For example the laser eye protec-ion filter T68 (Laservision GmbH & Co. KG, Germany)ffects responses across all three cones of the humanetina (Fig. 1). The color shift caused by this filter can beredicted by weighting the color matching functions withhe transmission curve of this filter. However, the evalu-tion of the perceptual change in color discrimination isore difficult. Clinical approaches for measurements of

olor discrimination aim to detect color defects. In gen-ral, pseudoisochromatic plate tests or arrangement testsre used to obtain qualitative information about color per-eption [1]. The disadvantage of these measurements liesn the use of colors of fixed spectral reflectance in combi-ation with the transmission curve of the filter media.or example, the results of the Farnsworth Munsell 100ue test [FM 100-test] with and without the filter T68

howed an increased error score measured with four sub-ects, but the error score with filter was still within theormal range (below 100) and had no significant de-reases at certain directions (Fig. 2). For quantitative as-essment of color defect levels, usually an anomaloscopes used [2], which works by using it with matching testsased on the principle of metamerism and using threearrowband light sources (Fig. 3). However, this method

s not applicable to measurements with filter media, as

1084-7529/09/102219-7/$15.00 © 2

he luminance modification may not be equal for bothest-field halves, and the color gamut is reduced comparedith human color perception.Color matching tests are a well-established method

sed in experimental surveys to detect influences of pa-ameters on different aspects of color vision, such as coloronstancy, adaptation or color induction. These applica-ions mostly employ standard cathode-ray tube (CRT) orhin-film transistor (TFT) displays [3–6]. Those displaysrovide a wide range of hue and luminance levels for theest field and context. However, using a display has im-ortant limitations when evaluating the change in coloriscrimination with colored filter media. Even the maxi-um luminance levels of the white point, which are com-only 200 cd/m2 for a CRT and 500 cd/m2 for a TFT, are

ot sufficient for measurements within the photopicange, especially for measurements with filters that haveow luminance transmittance. In addition, the analysis ofhe coherence between color perception and the cutoffavelength of filters requires a continuous spectrum at

his spectral range. In particular, the long wavelengthange is not covered because of a wavelength gap (Fig. 3).dditionally, more than three sources with narrowbandpectra for fine tuning the displayed colors through filteredia are needed. For example, with the filter T68 thisne tuning in color is almost impossible with the broad-and sources of a TFT monitor.The purpose of this study was to develop a measure-ent setup that allows detection of color discrimination

hresholds. The setup is designed to fulfill the require-

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2220 J. Opt. Soc. Am. A/Vol. 26, No. 10 /October 2009 Walter et al.

ents of “colorimetry by visual matching” [7] and toliminate all the above-mentioned disadvantages of CRTr TFT displays. Moreover, in each hue of the gamut,hich covers almost all of human color perception, a

reely adjustable spectrum can be generated. The impactf all influencing parameters on color perception is meanto be detectable and adjustable, as well as the evaluationf induced limitations on human color discrimination in-uced by colored filter media.

380 430 480 530 580 630 680 730 7800

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ig. 1. (Color online) Dotted curve denotes the transmissionpectra of the laser eye protection filter T68. Spectral shiftingimilar to color changes in the NSC color system [11] created theolor loci on the axes. This means that the intensity in one part ofhe spectrum is decreased when the complementary part isncreased.

ig. 2. (Color online) Specimen of the FM 100-test evaluatedith filter T68. The error score per chip is below 2 for unfiltered

ight for four subjects with normal color vision. With filter T68,he total error score increased for all subjects; however, it wastill within the normal range (below 100), and the specimensave no significant decreases at certain directions. The concen-ric circles correspond to the error score per chip that numbersre given with respect to the central circle.

. MATERIAL AND METHODShe apparatus employed in this investigation (Fig. 4) wasesigned to provide a color matching test with the follow-ng features: A vertically divided test field with a field ofiew [FOV] of 2°, an ambient field with a white color, mo-ocular observation, and a programmable presentationtrategy in combination with an adaptive measurementrocedure.

. Light Generationhe optical setup comprises two identical optical paths

one for each test field half). Light is generated by a two-et respective of seven different types of light emitting di-des (LEDs). Color generation is done by additive spectralolor mixing. The LEDs are selected to maintain continu-

380 430 480 530 580 630 680 730 780Wavelength (nm)

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ig. 3. (Color online) Characteristic line spectra (green, yellownd red solid lines) of an anomaloscope along with the light spec-rum as generated by a CRT display (solid curve on the left) andTFT monitor (dotted curve on the left). Especially at the longavelength range � � 600 nm the monitor spectra are not con-

inuous. The spectra have been measured with a spectrometer.ee text for equipment suppliers.

ig. 4. (Color online) Diagram of the measurement setup. Part: Light generation of the test field using LEDs and homoge-eous mixing in color and brightness by an “S” shaped optical fi-er. Part B: Principle of Koehler illumination; light bundle isruncated by a razor blade and mapped by a mirror on the testeld. Part C: Ambient field and back-shifted divided test field.art D: Ambient illumination with frosted glass plate. Part E:bservation lens allows adjustment of the FOV and eliminates

nstrumental myopia. The filter is positioned in front of the ob-ervation lens. The subject’s view of the test field is shown nexto the eye.

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Walter et al. Vol. 26, No. 10 /October 2009 /J. Opt. Soc. Am. A 2221

us spectra in the range from 420 nm to 750 nm. In Fig. 5he emission spectra of the seven LED types along withhe D65 illumination spectrum are shown [7]. Since directodulation of light flux by changing forward currentould be accompanied by a spectral shift of the semicon-uctor emission characteristics, this is avoided by using aulse width modulation (PWM) controller that keeps thelectrical current of the LEDs at a constant level and alsorovides a widely adjustable luminance range for eachED type. The forward currents of the LEDs used arehosen following the recommendation of the respectiveanufacturers (LED1, Germany; Nichia Corp., Japan;

nd Kingbright Electronic Co. Ltd., UK) for stability andifetime considerations. Depending on their luminous in-ensity, between two and fourteen LEDs of the same typere used per test field half (Table 1). The PWM frequencys chosen to be 120 Hz, which is much higher than theritical fusion frequency of the eye [7]. Each LED type se-ies connection can be modulated with a quantizationepth of 10 bit so that the pulse width directly corre-ponds to the luminance level. The LEDs are polished to

380 430 480 530 580 630 680 730 780Wavelength (nm)

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ig. 5. (Color online) Spectral curves of the seven LEDs (thinurves) along with the summation spectrum imitating D65 lightwide curve). The norm light D65 is shown for comparisondashed curve). The additive mixture of the LED spectra providescontinuous spectra within the range of 420 nm to 780 nm.

Table 1. Technical Data of the Seven

Color

DominantWavelength

(nm)

CIE CoCoordin

x

Blue 469 0.136Cyan 501 0.085Green 523 0.169Yellow 575 0.451Yellow 590 0.568Orange 603 0.649

Red 613 0.675

aSee text for instrument suppliers. Measured with a luminance and colorimetric

pproximate a Lambertian radiation profile in order tomprove the light coupling into an optical fiber (core di-meter 1 mm) by blunt coupling.All fibers are merged into a mixing waveguide (core di-

meter 10 mm) bent in an “S” shape (Fig. 4) to ensure aomogeneous mixture of luminance and color on the testeld for each required color coordinate. At the far end ofhe waveguide, the light is focused by a lens system basedn the principle of Koehler illumination, which maps alurred image of the fiber end on the test field. The lightath is truncated by a razor blade to gate out the corre-ponding test field half; the remaining path of the testeld half is positionable by a mirror on the test field (Fig.). Luminosities on the test field range between89 cd/m2 and 960 cd/m2 per LED series connectionTable 1) in steps of 0.6 cd/m2 to 1 cd/m2. Both test fieldsre arranged adjacent to each other without a visibleeparation line between them (Fig. 6). The test field itselfs positioned behind the ambient screen to avoid influencef the ambient light on the test field illumination. Thembient illumination is created by eight halogen lampsHalopar 16 Cool Beam reflector, 2900 K, Osram Ger-any) and a frosted glass plate, which was chosen for

ompatibility with the measurement setup published byacAdam, where the ambient illumination had a color

emperature of 2848 K [8]. The viewable ambient fieldize is adjustable by the field diaphragm of an observationens with a maximum FOV of 8°. This observation lensrovides refraction correction up to �1D (diopters), ensur-ng accommodation relaxation with monovision and pre-enting instrument myopia [9]. The head of the observers positioned on a headrest adjusted to the observationens, which maintains the arrangement of the tested eyeith respect to the optical axis of the setup during mea-

urement. The chin of the observer is placed on a chin restnd the forehead is placed against the forehead rest.

. Calibrationhe most important property of the measurement setup

or achievement of valid color discrimination thresholds ishe homogeneity of color over the test field halves and ho-ogeneity of luminance over the whole test field. Thesual luminance discrimination threshold is described inhe literature to be 1% [7] of the difference in illuminationevel at 377 cd/m2, valid only for differences with a sharp

s Used for the Measurement Setupa

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2222 J. Opt. Soc. Am. A/Vol. 26, No. 10 /October 2009 Walter et al.

order line and not for gradual transitions over the testeld. In the current test setup a small transition from theenter to the outer region of the test field was unavoidableue to the reflection properties of the mirrors. Betweenhe test field halves, a sharp borderline in color is visibleFig. 6). The luminance difference along the border line ofhe test field halves was 3 cd/m2 and beyond the lumi-ance discrimination threshold. Calibration measure-ents on the test field were performed with a luminance

nd colorimetric camera (Lumicam Color 1300, Instru-ent Systems, Germany). Measurement accuracy for that

amera was denoted �4% for luminance with repeatabil-ty of �0.1% (data by manufacturer). The measurementccuracy for color loci in the (x, y) chromaticity diagram isiven as �0.003 units and the repeatability for the coloroci is �0.0002 units. Measured color homogeneity overne test field half ranges around 0.0008 units in the (x, y)hromaticity diagram and therefore lies beyond the coloriscrimination thresholds published by MacAdam [8]. Ad-itionally the distance of adjacent points on one axis of aolor ellipse is approximately 0.003 units in the (x, y)hromaticity diagram. The challenge of this measurementetup was to reconcile the chromaticity coordinate, the lu-inance level, and the shape of the spectrum. After se-

ecting a reference color in the (x, y) chromaticity dia-ram, the form of the spectrum and the luminance levelre adjusted by controlling each LED type separately. Forhe spectral calibration measurements, we use a spec-rometer (USB 2000, Ocean Optics, USA) to control theontinuity of the spectrum.

. Measurement Procedures spectral radiation of the same LED circuit in each

ight path is not identical, color calibration for both lightaths is needed for both test field halves separately. Theue of one test field half is kept constant at one color co-rdinate. The complementary test field half is used forresenting the hue along semimeridians in the (x, y) chro-aticity diagram (Fig. 7). In our initial measurements,

he overall luminance level (without filter) is fixed at

ig. 6. (Color online) Measurement strategy: First the subject iseutral-adapted by the same color as the ambient field. Then theentral point of the ellipse and the outermost color lying on one ofhe measurement axes are presented. If the answer is “yes” (aolor difference could be seen), a point closer to the center isaken; a farther point is chosen if the answer is “no.” The subjectas to decide whether a color difference is visible or not. After thehosen presentation time, the stimulus is changed to neutral ad-ptation again. Then a new color discrimination stimulus is pre-ented, the location on the axis depending on the previous an-wer given. Color differences in the image are enhanced foretter display.

77 cd/m2. The starting color is a yellowish hue at coor-inate (0.4664,0.4528) in the (x, y) chromaticity diagramnd corresponds to the center of the resulting color dis-rimination ellipse. The spectrum of this color coordinates continuous (Fig. 1). Based on this coordinate six half-xes are defined to ensure sufficient thresholds for ellipsetting [10]. Of these, three half-axes are chosen along theonfusion lines of deuteranomaly, protanomaly, and trita-omaly [7] (Fig. 7). On each axis, at least six color coordi-ates are spectrally defined for presentation. On the basisf the principle of metamerism, there is more than oneay to generate the same chromaticity coordinate withifferent spectra because of the seven different LED emis-ion spectra. Spectral shifting similar to color changes inhe NSC color system [11] create the color loci on the axes.his means that the intensity in one part of the spectrum

s decreased when the complementary part is increasedFig. 1). Initially, one test field half presents the hue of thellipse center, while the other half presents the outermostefined point of the tested axis, which is an easily distin-uishable stimulus.

Stimuli are shown for 900 ms following a neutral adap-ation phase of 2700 ms (Fig. 6). The hue of the neutraldaptation phase is close to a color temperature of 2900 K7] at (0.447,0.407). This is done to control chromatic ad-ptation of the test field, unlike the measurement proce-ure of MacAdam. The next color point is then chosen de-ending on the subject’s answer. If the answer is “yes” (aolor difference could be seen), a point closer to the centers taken; a farther point is chosen if the answer is “no.”his “staircase” method is used to determine the visual

hreshold within an appropriate time, having a confidenceevel of 0.5. After the first two inflections, the mean valuef the following six inflection points is defined as the coloriscrimination threshold on this axis. The control strat-gy is implemented in a computer program where the pre-entation times of the matching colors are at least 300 msadjustable), the generation and storing lists are named,nd subjects’ data can be entered. The measurement of

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ig. 7. (Color online) Starting color is a yellowish hue at coor-inate (0.4664,0.4528) in the (x, y) chromaticity diagram and cor-esponds to the center of the resulting color discrimination el-ipse. Based on this coordinate six half-axes are defined. Of these,hree half-axes are chosen along the confusion lines of deutera-omaly, protanomaly, and tritanomaly [7].

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Walter et al. Vol. 26, No. 10 /October 2009 /J. Opt. Soc. Am. A 2223

he color discrimination thresholds for one subject on sixalf-axes took approximately 20 min per eye.

. Reliabilityeliability in psychological and physiological research isften quantified using Cronbach’s � coefficient, which de-cribes the mean of all split-half reliabilities [12]. For thisnvestigation we calculate the color distances in the (x, y)hromaticity diagram (central color coordinate to thehresholds) of 18 subjects on each axis for three measure-ents. The results were statistically validated usingronbach’s � reliability test in SPSS 16.0 (SPSS, SPSS

nc., Chicago), which resulted in values between 0.701nd 0.880 on different axes (Table 2), which is a com-only acceptable range for a unidimensional test with

ew items [12].

. Measurement with Transparent Filter Mediafter assessment of color discrimination thresholds fornfiltered sight, measurements were repeated with oneolored laser eye protection filter (Model T68—aserVision GmbH & Co. KG; transmission curve in Fig.) which is placed in front of the observation lens. Thus,he color coordinate of the starting point is shifted to areen hue (0.3143,0.5191) as well as the ambient color,hich equates to the adaptation color (0.2938,0.493) in

he (x, y) chromaticity diagram. The overall luminanceehind the filter (eye side) was fixed at 307 cd/m2. There-ore, the luminance of the color points on the axes was re-djusted and additional color points had to be defined be-ause of the reduction of sensitivity caused by the overalluminous transmittance of the filter. The spectral shapet the respective color points was kept constant. The hueor the neutral adaptation phase was adapted to matchhe ambient light corrected for the filter losses. The mea-urement procedure was the same as described above fornfiltered sight.

. Transformation of the Discrimination Thresholdshe color discrimination thresholds of each axis and sub-

ect were transformed to the CIE 1976 USC chromaticityiagram [�u� ,v�� chromaticity diagram] with the follow-ng equations [13]:

u� = 4x/�− 2x + 12y + 3�, �1�

v� = 9y/�− 2x + 12y + 3�. �2�

The �u� ,v�� chromaticity diagram may be used insteadf a true uniform chromaticity scale surface. In this chro-

Table 2. Reliability of the Color Distancesain the (xfor Three

Axis Mean Value Std. Dev. M

1 0.0045 0.00182 0.0043 0.00183 0.0083 0.00254 0.0046 0.00215 0.0036 0.00156 0.0056 0.0023

aCentral color coordinate to the thresholds.

aticity diagram, MacAdam’s ellipses approach more aircular shape of equal size. The advantage of this chro-aticity diagram is the good approximation of human

olor perception that implicates an equidistant color met-ic. The geometrical color distances �Eu�,v� between theentral hue and the six color discrimination thresholdsere calculated using the metric

�Eu�,v� = ���u��2 + ��v��2. �3�

. Fitting and Averaging of Ellipsesfter detection of the color discrimination thresholds and

ransformation into the �u� ,v�� chromaticity diagram, el-ipses were fitted to these thresholds, respectively, by ap-lying a least-squares method [10]. The center of the el-ipses was not fixed to the central color coordinate useduring measurement. Finally the ellipses were averagedsing a multivariant vector analysis over the components

hromaticity Diagram of 18 Subjects on Each Axisurements

inimum Mean Maximum Cronbach’s �

21 0.0093 0.70122 0.0088 0.75139 0.0130 0.73117 0.0089 0.86719 0.0086 0.88020 0.0091 0.704

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2224 J. Opt. Soc. Am. A/Vol. 26, No. 10 /October 2009 Walter et al.

, C0, and C45 with the parameters’ semimajor axis A,emiminor axis B, and the angle � (Fig. 8). These vectoromponents follow the power vector notation commonlysed in ophthalmic optics [14].

S = B + �A − B�/2, �4�

C0 = �A − B�cos�2��, �5�

C45 = �A − B� � sin�2��. �6�

. RESULTS. Validation over Color Vision Deficienciese conducted validation measurements with an anomalo-

cope (HMC-Anomaloscope, Oculus GmbH & Co. KG,ermany). Thirty-one people with normal color vision and

wo people with known congenital color deficiencies vol-nteered for this study. All subjects underwent testing forolor deficiencies of protanomaly and deuteranomaly withhe anomaloscope, which showed that all subjects withresumably normal color vision were indeed within theormal range between 34 and 46 [2](Table 3). The sub-

ects with known color deficiencies could be identified asrotanomalous (subject 1) and deuteranomalous (subject) [2]. The determination of the color discriminationhresholds with the described measurement system wasone on two axes (b and e) around the central hue (Fig. 8).he orientations of these axes were parallel to the confu-ion lines of color deficient people [2]. The color deficientubjects showed significantly �p�0.05� larger color dis-rimination thresholds along the color confusion lineshan the subjects with normal color vision (Table 3). The

Table 3. Validation Measureme

Subjectsb AgeAnomaloscopeMean Value

Normal group 28.2 39.3Subject 1 36 49.7Subject 2 29 21.3

aSee text for equiment suppliers.bSee text for subject and procedural information. Thirty-one people with normal

tudy. All subjects underwent testing for color deficiencies of protanomaly and deutolor vision were indeed within the normal range between 34 and 46 �2�. The sueuteranomalous �subject 2� �2�. The determination of the color discrimination threentral hue �Fig. 8�. The orientations of these axes were parallel to the confusion lin

Table 4. Comparison of Discrimination Ellipseswith and without Filter T68a

Ellipse Parameter MacAdam Data Free Sight T68

Center u� 0.185 0.249 0.174Center v� 0.545 0.543 0.543

Semimajor axis �A� 0.0013 0.003 0.005Semiminor axis �B� 0.0008 0.0023 0.001

� (in degrees) 113.0 10.43 26.29 (eccentricity) 0.775 0.642 0.969

aAccomplished by shifting the central color coordinate �not the ellipse center� tohe origin of the �u ,v � chromaticity diagram.

� �

rotanomalous subject showed larger thresholds in axis b,hile both subjects, deuteranomalous and protanoma-

ous, showed larger thresholds in axis e, which allows dis-rimination of both anomalies. The results show that theresented measurement setup is suitable for detectionnd discrimination of color defects.

. Color Discrimination with and without Filter Mediae repeated three measurements for free sight and use of

he laser eye protection filter T68 with five color-normalubjects. Afterwards ellipses were fitted through thehresholds for one eye of each subject. To determine theffect of the filter on color discrimination, the ellipseseasured with this filter were averaged over five subjects

nd all three repeats per condition (Table 4). Comparisonf ellipses with and without filter was accomplished byhifting the central color coordinate (not the ellipse cen-er) to the origin of the (u�, v�) chromaticity diagram (Fig.). Transformation to the (u�, v�) chromaticity diagramnabled analysis of the differences of the discriminationllipses in the different directions: red–green (horizontalrientation) as well as blue–yellow (vertical direction).ignificant differences �p�0.001� were detected betweenoth ellipses (with and without filter, see Table 4. Weound that the angle of the semimajor axis changed from0° (free sight) to 26° with filter T68. In addition, theemimajor axis was increased whereas the semiminorxis was decreased. This means that the color discrimina-ion sensitivity in the green–yellow and the violet range isncreased, whereas in the cyan and yellow–red, range, its decreased while using the filter.

. DISCUSSIONhis novel measurement setup represents a tool suitable

or almost all kinds of color matching tests. Although itannot simulate the exact narrowband light sources of annomaloscope, it can be used to measure color discrimina-ion thresholds along confusion lines. If people suffer fromolor defects, the discrimination thresholds along the con-usion lines are decreased [15]. With our instrument, thisan now be verified over almost the whole gamut of hu-an color perception. The capability to detect color de-

ects was tested in a population study of 33 subjects, twof whom were color deficient. The results were compa-able to those obtained using an anomaloscope. It wasound that the color discrimination thresholds of the sub-

Subjects with Anomaloscopea

Median Threshold�Eu�,v�

Number ofMeasurementsb (Protan) e (Deutan)

3.776 3.412 110.37 6.88 22.168 10.638 9

ision and two people with known congenital color deficiencies volunteered for thisly with the anomaloscope, with the result that all subjects with presumably normalith known color deficiencies could be identified as protanomalous �subject 1� andith the described measurement system was done on two axes �b and e� around thelor deficient people �7�.

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Walter et al. Vol. 26, No. 10 /October 2009 /J. Opt. Soc. Am. A 2225

ects with color defects were significantly higher thanhose of subjects with normal color vision.

Changes in color perception caused by glaucoma aresually evaluated by the hue discrimination measuredith the FM 100-hue test administered under standard il-

umination C lighting conditions. The discriminationhresholds for people suffering from glaucoma are signifi-antly increased for plates along an axis produced byhanges only in S-cone input [16]. A clinical applicationor our setup could be the early-stage detection of glau-oma disease. The measurement of increased color dis-rimination thresholds along the tritanopia confusion lineould be an indication factor of the changed color percep-ion caused by glaucoma.

The parameters of influence on color discrimination byolor matching tests, such as adaptation time, luminanceevel, or ambient color (based on a monocularly viewed 2°plit field) could be alternatively measured using theetup described here. The adjustable large range of lumi-ance and chromaticity is one advantage compared withRT or TFT displays. For example, the determination of

he white point in unnatural saturated surroundings,imilar to the measurements of Kiriki and Uchikawa in998 [17], could be remeasured and compared with mea-urements on more natural luminance levels (above0 cd/m2).Regarding the color discrimination thresholds firsteasured by MacAdam in 1942 [8], many questions re-ain unanswered, for example, whether the ellipses stay

onstant for different luminance levels. MacAdam em-loyed a luminance level of �60 cd/m2, quite low withinhe photopic range. If there is a dependence between theuminance level and the angle of discrimination ellipses,s Brown predicted in 1952 [18], this could be analyzed inwide luminance range.With this setup, the determination of changes in color

erception with and without colored filter media is repro-ucibly measurable for the first time. To retain a realisticeasurement procedure, the filter could be placed di-

ectly in front of the observation lens. Thus, the ambientight would also be affected by the filter media. In con-rast to the setup published by MacAdam, adaptationould be controlled by a time limited measurement proto-ol with strict time management. This would lead to bet-er color discrimination in MacAdam-type measurementsnd in turn rather small ellipses. This could be demon-trated by overlaying our measurement with the nearestacAdam ellipse [central hue (0.3796; 0.4978) in the (x,

) chromaticity diagram [8]], which was transformed andhifted into the origin of the (u�, v�) chromaticity diagramFig. 8). In the filter condition, discrimination thresholdsecreased, which was reflected by the shortened ellipses.his suggests that these filters can increase color dis-rimination thresholds in specific color regions. Future re-

earch will address the possibility of producing and test-

ng vision-enhancing protection filters for optimized coloriscrimination based on the shape of the transmissionpectra.

. CONCLUSIONShe presented measurement setup was shown to be a uni-ersal instrument for the measurement of various param-ters in color perception via matching tests. We couldemonstrate the system’s capability of detecting color de-ciencies in a patient survey in comparison with annomaloscope. Measurements of color perception with la-er eye protection filters showed a significant change ofhe color discrimination thresholds compared to thoseith unfiltered vision.

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