Most empirical work on color constancy is based on simple laboratory models of natural viewing conditions. These typically consist of spots seen against uniform backgrounds or computer simulations of flat surfaces seen under spatially uniform illumination. In this study measurements were made under more natural viewing conditions. Observers used a projection colorimeter to adjust the appearance of a test patch until it appeared achromatic. Observers made such achromatic settings under a variety of illuminants and when the test surface was viewed against a number of different backgrounds. An analysis of the achromatic settings reveals that observers show good color constancy when the illumination is varied. Changing the background surface against which the test patch is seen, on the other hand, has a relatively small effect on the achromatic loci. The results thus indicate that constancy is not achieved by a simple comparison between the test surface and its local surround.
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Chromaticities and Luminances of Illuminants and Backgroundsa
Experiment 1
Blue Illuminant
Yellow Illuminant
CIE
CIE
Lum.
CIE
CIE
Lum.
Illuminant (gray background)
0.353
0.373
13.6
0.509
0.418
15.2
Illuminant (all backgrounds)
0.346
0.371
13.6
0.509
0.419
16.3
Gray background
0.463
0.463
0.5
0.555
0.555
0.6
Red background
0.622
0.622
0.6
0.368
0.368
0.4
Yellow background
0.515
0.515
0.5
0.553
0.553
0.6
Dark Blue background
0.236
0.298
1.6
0.416
0.412
1.5
Brown background
0.468
0.394
2.2
0.581
0.394
3.4
Black background
0.349
0.369
0.6
0.515
0.415
0.7
White background
0.355
0.379
11.6
0.515
0.420
14.5
Experiment 2
CIE
CIE
Lum.
Illuminant 0
0.412
0.403
18.3
Illuminant 1
0.305
0.396
18.0
Illuminant 2
0.403
0.300
19.9
Illuminant 3
0.403
0.498
17.4
Illuminant 4
0.486
0.407
17.3
Illuminant 5
0.293
0.309
19.5
Illuminant 6
0.491
0.314
20.4
Illuminant 7
0.312
0.490
18.1
Illuminant 8
0.474
0.482
18.4
The top half of the table gives values for Experiment 1. There is some session-to-session variability in the measured values. The top line specifies the Blue and Yellow illuminants averaged over all sessions where the Gray background was used. The second line specifies the same illuminants averaged over all sessions in Experiment 1. The chromaticities and luminances of the light reflected to the observer from the background surfaces are specified for the two experimental illuminants. The specified values were obtained by averaging over all sessions in which the particular background surface was used. The bottom half of the table provides the chromaticities and luminances of the nine experimental illuminants used in Experiment 2, obtained by averaging across sessions.
The top half of the table gives the indices computed for each observer/background pair in Experiment 1. The average constancy index for the Gray background is 0.84. The average constancy index for all observer/background pairs for the five observers is 0.85. The background indices were computed with respect to the Gray background surface for both the Blue and the Yellow illuminants. The average background index for the Blue illuminant is 0.07 and for the Yellow illuminant is 0.08. The bottom half of the table gives the constancy indices for Experiment 2 for illuminants 1–8, computed with respect to illuminant 0. The average index is 0.87 for observer JAD and 0.84 for observer DHB.
The top section of the table provides the chromaticities and luminances of the seven experimental illuminants used in Experiments 3 and 6. The design of Experiments 3 and 6 was identical except for the adjustment starting rule used. The table provides the average of the stimulus measurements made for the two experiments. The middle section provides the chromaticities and luminances of the light reflected to the observer from the Gray background surface under the seven illuminants. The bottom section gives the chromaticities and luminances of the light reflected to the observer from the seven background surfaces under the Gray illuminant. For symmetry, the data for the Gray background surface under the Gray illuminant is provided in both the middle and bottom sections.
Table 4
Constancy and Background Indices for Experiment 3, Observer DHBa
Illuminant/Background
Change Illuminant
Change Background: BI
CI
BI
Red
0.80
0.80
0.07
Yellow
0.91
0.89
0.24
Dark Blue
0.80
0.80
0.13
Light Blue
0.76
0.78
0.18
Light Green
0.64
0.71
Pale Yellow
0.91
0.91
0.37
CI, constancy index; BI, background index. The first column provides the constancy indices for the conditions measured with the Gray background surface, computed for each illuminant with respect to the Gray illuminant. The mean of these indices is 0.80. The second column provides the background indices for the same observer computed for the same conditions. Since the chromaticity of the light reflected from the Gray background surface is close to that of the illuminant, these background indices are very close to the constancy indices. The mean of these indices is 0.82. The third column provides the background indices computed when the illuminant (Gray) was held fixed and the background surface was changed, computed with respect to the data obtained with the Gray background surface. The mean of these indices is 0.15. If the effect of the illuminant were governed entirely by simultaneous contrast from the background surface, the two sets of background indices should be identical. In fact, they differ considerably.
Table 5
Constancy and Background Indices for Experiment 5, Observer JPHa
Background Surface
CI
BI
RCI
No Cloth
Red Cloth
No Cloth
Red Cloth
Blue Illum.
Yellow Illum.
Blue Illum.
Yellow Illum.
Blue Illum.
Yellow Illum.
Gray
0.93
0.84
0.10
0.10
Red
0.86
0.68
0.12
0.10
0.08
0.01
0.07
0.03
Yellow
0.87
0.72
0.17
0.14
0.13
0.05
0.04
Dark Blue
0.86
0.84
0.01
0.20
0.18
0.03
0.04
Mean
0.88
0.77
0.08
0.08
0.13
0.03
0.06
0.05
Mean (Blue/Yellow)
0.08
0.08
0.06
CI, constancy index; BI, background index. The first column provides the constancy indices measured for the change from Blue to Yellow illuminant in the condition where the red cloth was not present. The second column gives the same indices when the red cloth was present. The third through sixth columns give the background indices (computed with respect to the Gray background surface) for each background surface under each illuminant both with and without the red cloth. The final two columns give the red cloth indices under the Blue and Yellow illuminants. The second to last row of the table provides the means of each column, while the last row consolidates these means (where applicable) across the Blue and Yellow illuminants.
Table 6
Constancy and Background Indices for Experiments 6 and 7a
Experiment 6, Observer WAB
Illuminant/Background
Change Illuminant
Change Background
CI
BI
BI
Red
0.95
0.96
0.32
Yellow
0.91
0.87
0.76
Dark Blue
0.70
0.68
Light Blue
0.86
0.86
0.20
Light Green
0.53
0.61
0.41
Pale Yellow
0.94
0.91
0.71
Experiment 7
Illuminant/Background
Change Illuminant
Change Background
CI
BI
BI
MDR
DHB
JMK
MDR
DHB
JMK
MDR
DHB
JMK
Yellow
0.86
0.92
0.77
0.86
0.93
0.78
0.34
0.41
0.13
CI, constancy index; BI, background index. The top part of the table is in the same format as in Table 4. The first column provides the constancy indices for the conditions measured with the Gray background surface, computed for each illuminant with respect to the Gray illuminant. The mean of these indices is 0.82. The second column provides the background indices for the same observer computed for the same conditions. Since the chromaticity of the light reflected from the Gray background surface is close to that of the illuminant, these background indices are very close to the constancy indices. The mean of these indices is 0.82. The third column provides the background indices computed when the illuminant was held fixed (it was the Gray illuminant) and the background surface was changed, computed with respect to the data obtained with the Gray background surface. The mean of these indices is 0.39. The bottom part provides the same information for Experiment 7, for three observers. Each group of three columns in the bottom part of the figure corresponds to one column in the top part.
This experiment is analogous to Experiment 3, but only one illuminant/background surface pair was investigated. The top section provides the chromaticities and luminances of the two experimental illuminants. The middle section provides the chromaticities and luminances of the light reflected to the observer from the Gray background surface under these two illuminants. The bottom section gives the chromaticities and luminances of the light reflected to the observer from the two background surfaces under the Gray illuminant. For symmetry, the data for the Gray background under the Gray illuminant is provided in both the middle and bottom sections.
Tables (7)
Table 1
Chromaticities and Luminances of Illuminants and Backgroundsa
Experiment 1
Blue Illuminant
Yellow Illuminant
CIE
CIE
Lum.
CIE
CIE
Lum.
Illuminant (gray background)
0.353
0.373
13.6
0.509
0.418
15.2
Illuminant (all backgrounds)
0.346
0.371
13.6
0.509
0.419
16.3
Gray background
0.463
0.463
0.5
0.555
0.555
0.6
Red background
0.622
0.622
0.6
0.368
0.368
0.4
Yellow background
0.515
0.515
0.5
0.553
0.553
0.6
Dark Blue background
0.236
0.298
1.6
0.416
0.412
1.5
Brown background
0.468
0.394
2.2
0.581
0.394
3.4
Black background
0.349
0.369
0.6
0.515
0.415
0.7
White background
0.355
0.379
11.6
0.515
0.420
14.5
Experiment 2
CIE
CIE
Lum.
Illuminant 0
0.412
0.403
18.3
Illuminant 1
0.305
0.396
18.0
Illuminant 2
0.403
0.300
19.9
Illuminant 3
0.403
0.498
17.4
Illuminant 4
0.486
0.407
17.3
Illuminant 5
0.293
0.309
19.5
Illuminant 6
0.491
0.314
20.4
Illuminant 7
0.312
0.490
18.1
Illuminant 8
0.474
0.482
18.4
The top half of the table gives values for Experiment 1. There is some session-to-session variability in the measured values. The top line specifies the Blue and Yellow illuminants averaged over all sessions where the Gray background was used. The second line specifies the same illuminants averaged over all sessions in Experiment 1. The chromaticities and luminances of the light reflected to the observer from the background surfaces are specified for the two experimental illuminants. The specified values were obtained by averaging over all sessions in which the particular background surface was used. The bottom half of the table provides the chromaticities and luminances of the nine experimental illuminants used in Experiment 2, obtained by averaging across sessions.
The top half of the table gives the indices computed for each observer/background pair in Experiment 1. The average constancy index for the Gray background is 0.84. The average constancy index for all observer/background pairs for the five observers is 0.85. The background indices were computed with respect to the Gray background surface for both the Blue and the Yellow illuminants. The average background index for the Blue illuminant is 0.07 and for the Yellow illuminant is 0.08. The bottom half of the table gives the constancy indices for Experiment 2 for illuminants 1–8, computed with respect to illuminant 0. The average index is 0.87 for observer JAD and 0.84 for observer DHB.
The top section of the table provides the chromaticities and luminances of the seven experimental illuminants used in Experiments 3 and 6. The design of Experiments 3 and 6 was identical except for the adjustment starting rule used. The table provides the average of the stimulus measurements made for the two experiments. The middle section provides the chromaticities and luminances of the light reflected to the observer from the Gray background surface under the seven illuminants. The bottom section gives the chromaticities and luminances of the light reflected to the observer from the seven background surfaces under the Gray illuminant. For symmetry, the data for the Gray background surface under the Gray illuminant is provided in both the middle and bottom sections.
Table 4
Constancy and Background Indices for Experiment 3, Observer DHBa
Illuminant/Background
Change Illuminant
Change Background: BI
CI
BI
Red
0.80
0.80
0.07
Yellow
0.91
0.89
0.24
Dark Blue
0.80
0.80
0.13
Light Blue
0.76
0.78
0.18
Light Green
0.64
0.71
Pale Yellow
0.91
0.91
0.37
CI, constancy index; BI, background index. The first column provides the constancy indices for the conditions measured with the Gray background surface, computed for each illuminant with respect to the Gray illuminant. The mean of these indices is 0.80. The second column provides the background indices for the same observer computed for the same conditions. Since the chromaticity of the light reflected from the Gray background surface is close to that of the illuminant, these background indices are very close to the constancy indices. The mean of these indices is 0.82. The third column provides the background indices computed when the illuminant (Gray) was held fixed and the background surface was changed, computed with respect to the data obtained with the Gray background surface. The mean of these indices is 0.15. If the effect of the illuminant were governed entirely by simultaneous contrast from the background surface, the two sets of background indices should be identical. In fact, they differ considerably.
Table 5
Constancy and Background Indices for Experiment 5, Observer JPHa
Background Surface
CI
BI
RCI
No Cloth
Red Cloth
No Cloth
Red Cloth
Blue Illum.
Yellow Illum.
Blue Illum.
Yellow Illum.
Blue Illum.
Yellow Illum.
Gray
0.93
0.84
0.10
0.10
Red
0.86
0.68
0.12
0.10
0.08
0.01
0.07
0.03
Yellow
0.87
0.72
0.17
0.14
0.13
0.05
0.04
Dark Blue
0.86
0.84
0.01
0.20
0.18
0.03
0.04
Mean
0.88
0.77
0.08
0.08
0.13
0.03
0.06
0.05
Mean (Blue/Yellow)
0.08
0.08
0.06
CI, constancy index; BI, background index. The first column provides the constancy indices measured for the change from Blue to Yellow illuminant in the condition where the red cloth was not present. The second column gives the same indices when the red cloth was present. The third through sixth columns give the background indices (computed with respect to the Gray background surface) for each background surface under each illuminant both with and without the red cloth. The final two columns give the red cloth indices under the Blue and Yellow illuminants. The second to last row of the table provides the means of each column, while the last row consolidates these means (where applicable) across the Blue and Yellow illuminants.
Table 6
Constancy and Background Indices for Experiments 6 and 7a
Experiment 6, Observer WAB
Illuminant/Background
Change Illuminant
Change Background
CI
BI
BI
Red
0.95
0.96
0.32
Yellow
0.91
0.87
0.76
Dark Blue
0.70
0.68
Light Blue
0.86
0.86
0.20
Light Green
0.53
0.61
0.41
Pale Yellow
0.94
0.91
0.71
Experiment 7
Illuminant/Background
Change Illuminant
Change Background
CI
BI
BI
MDR
DHB
JMK
MDR
DHB
JMK
MDR
DHB
JMK
Yellow
0.86
0.92
0.77
0.86
0.93
0.78
0.34
0.41
0.13
CI, constancy index; BI, background index. The top part of the table is in the same format as in Table 4. The first column provides the constancy indices for the conditions measured with the Gray background surface, computed for each illuminant with respect to the Gray illuminant. The mean of these indices is 0.82. The second column provides the background indices for the same observer computed for the same conditions. Since the chromaticity of the light reflected from the Gray background surface is close to that of the illuminant, these background indices are very close to the constancy indices. The mean of these indices is 0.82. The third column provides the background indices computed when the illuminant was held fixed (it was the Gray illuminant) and the background surface was changed, computed with respect to the data obtained with the Gray background surface. The mean of these indices is 0.39. The bottom part provides the same information for Experiment 7, for three observers. Each group of three columns in the bottom part of the figure corresponds to one column in the top part.
This experiment is analogous to Experiment 3, but only one illuminant/background surface pair was investigated. The top section provides the chromaticities and luminances of the two experimental illuminants. The middle section provides the chromaticities and luminances of the light reflected to the observer from the Gray background surface under these two illuminants. The bottom section gives the chromaticities and luminances of the light reflected to the observer from the two background surfaces under the Gray illuminant. For symmetry, the data for the Gray background under the Gray illuminant is provided in both the middle and bottom sections.