Journal of
J. Math. Biology 8, 47-53 (1979)
Ilkdhml
mi
by Springer-Verlag 1979
Color Perception and the Limits of Color Constancy (3. West* Department of Physics, Philipps University, D-3550 Marburg, Federal Republic of Germany
Snmmal~.. A summary of colorimetry is ~ven and the limits of color constancy mechanism under changing illuminations are discussed. Key words: Colorimetry - - Color perception - - Color constancy.
9 The fact remains that objects retain their color identity under a great variety of lighting conditions. This constancy is not a minor second-order effect but is so fundamental... [Land]
1. The Experience of Color Constancy Color constancy in color perception is achieved by nervous processes, whose effect can be demonstrated by photographing a daylight scene with a tungsten color film or a tungsten-lighted scene with a daylight color film. (The photographer tries to compensate the effects of different illumination by changing film type or use of filters.) Nevertheless, Resnikoff's [5] following description of color constancy must be further clarified: ' . . . Thus, since not only the intensity but also the color of illumination in a daylight-lit gallery varies depending on the time of day, the cloud cover, and the season without significantly affecting the relative hues, saturation, or brightness of components of the exhibited paintings, we must conclude that their relative properties are independent of the state of illumination throughout a large region of color space which includes all normal conditions of illumination. That it is not necessary to relearn color relations when one uses tinted sunglasses or drives an automobile with a tinted windshield provides additional corroboration, and the essentially interchangeable use of incandescant and fluorescent illuminants supports this contention in still another way.
*
Present address:
Bergstrasse 14a, D-5060 Bergisch Gladbach 2
0303-6812/79/0008/0047/$01.40
48
G. West Examples of changes of background illumination are provided by the varying illumination provided by sunlight as a function of the time of day and the cloud cover, by the transformation induced by replacement of a daylight illuminant by a typical incandescent or fluorescent illuminant, and by the transformation of background induced by the use of sunglasses or other filtering media.'
Resnikoff's remarks cannot be generally accepted, because Ishihara's Test Cards for Colour Blindness are a counter example. If the illumination deviates too large from the norm, or if one looks through a filter at the test cards, then the normal trichromatic human observer sees the patterns that show color deficiency. (The name 'pseudo-isochrqmatische Tafeln' originating from Stilling [6] underlines this property of the test cards.) W. MaaB described to the author the existence of pictures in a church in Tender (Denmark) related to this phenomena: the appearance of the pictures varies with illumination. Nevertheless, as noticed by Resnikoff, in most cases a change of illumination is not followed by a change in color perception. The reason for this must be a consequence of the particular properties of the pigments used by the artist and generally found in nature. A theoretical analysis will confirm this hypothesis and on the other hand show its limits. 2. The Color Space Colorimetry [6, 7] and color perception [I] are based on the homomorphism from the set of physical lights onto the color space ~. The spectral decomposition of the physical lights, i.e. radiation falling on the retina, is represented by a f u n c t i o n f / -L
f(h) >1 O,
| f ( h ) dh < oo,S
J. Math. Biology 8, 47-53 (1979)
Ilkdhml
mi
by Springer-Verlag 1979
Color Perception and the Limits of Color Constancy (3. West* Department of Physics, Philipps University, D-3550 Marburg, Federal Republic of Germany
Snmmal~.. A summary of colorimetry is ~ven and the limits of color constancy mechanism under changing illuminations are discussed. Key words: Colorimetry - - Color perception - - Color constancy.
9 The fact remains that objects retain their color identity under a great variety of lighting conditions. This constancy is not a minor second-order effect but is so fundamental... [Land]
1. The Experience of Color Constancy Color constancy in color perception is achieved by nervous processes, whose effect can be demonstrated by photographing a daylight scene with a tungsten color film or a tungsten-lighted scene with a daylight color film. (The photographer tries to compensate the effects of different illumination by changing film type or use of filters.) Nevertheless, Resnikoff's [5] following description of color constancy must be further clarified: ' . . . Thus, since not only the intensity but also the color of illumination in a daylight-lit gallery varies depending on the time of day, the cloud cover, and the season without significantly affecting the relative hues, saturation, or brightness of components of the exhibited paintings, we must conclude that their relative properties are independent of the state of illumination throughout a large region of color space which includes all normal conditions of illumination. That it is not necessary to relearn color relations when one uses tinted sunglasses or drives an automobile with a tinted windshield provides additional corroboration, and the essentially interchangeable use of incandescant and fluorescent illuminants supports this contention in still another way.
*
Present address:
Bergstrasse 14a, D-5060 Bergisch Gladbach 2
0303-6812/79/0008/0047/$01.40
48
G. West Examples of changes of background illumination are provided by the varying illumination provided by sunlight as a function of the time of day and the cloud cover, by the transformation induced by replacement of a daylight illuminant by a typical incandescent or fluorescent illuminant, and by the transformation of background induced by the use of sunglasses or other filtering media.'
Resnikoff's remarks cannot be generally accepted, because Ishihara's Test Cards for Colour Blindness are a counter example. If the illumination deviates too large from the norm, or if one looks through a filter at the test cards, then the normal trichromatic human observer sees the patterns that show color deficiency. (The name 'pseudo-isochrqmatische Tafeln' originating from Stilling [6] underlines this property of the test cards.) W. MaaB described to the author the existence of pictures in a church in Tender (Denmark) related to this phenomena: the appearance of the pictures varies with illumination. Nevertheless, as noticed by Resnikoff, in most cases a change of illumination is not followed by a change in color perception. The reason for this must be a consequence of the particular properties of the pigments used by the artist and generally found in nature. A theoretical analysis will confirm this hypothesis and on the other hand show its limits. 2. The Color Space Colorimetry [6, 7] and color perception [I] are based on the homomorphism from the set of physical lights onto the color space ~. The spectral decomposition of the physical lights, i.e. radiation falling on the retina, is represented by a f u n c t i o n f / -L
f(h) >1 O,
| f ( h ) dh < oo,S
