Chromatic adaptation
Encyclopedia
Chromatic adaptation
is one aspect of vision that may fool someone into observing a color-based optical illusion
, such as the same color illusion
.
An object may be viewed under various conditions. For example, it may be illuminated by sunlight, the light of a fire, or a harsh electric light. In all of these situations, human vision perceives that the object has the same color: an apple always appears red, whether viewed at night or during the day. On the other hand, a camera with no adjustment for light may register the apple as having varying color. This feature of the visual system is called chromatic adaptation, or color constancy
; when the correction occurs in a camera it is referred to as white balance.
Though the human visual system generally does maintain constant perceived color under different lighting, there are situations where the relative brightness of two different stimuli will appear reversed at different illuminance
levels. For example, the bright yellow petals of flowers will appear dark compared to the green leaves in dim light while the opposite is true during the day. This is known as the Purkinje effect
, and arises because the peak sensitivity of the human eye shifts toward the blue end of the spectrum at lower light levels.
spectral sensitivity responses so as to keep the adapted appearance of the reference white constant. The application of Johannes von Kries
's idea of adaptive gains on the three cone cell
types was first explicitly applied to the problem of color constancy by Herbert E. Ives
, and the method is sometimes referred to as the Ives transform or the von Kries–Ives adaptation.
The von Kries coefficient rule rests on the assumption that color constancy
is achieved by individually adapting the gains of the three cone responses, the gains depending on the sensory context, that is, the color history and surround. Thus, the cone responses
from two radiant spectra can be matched by appropriate choice of diagonal adaptation matrices D1 and D2:
where
is the cone sensitivity matrix and 
is the spectrum of the conditioning stimulus. This leads to the von Kries transform for chromatic adaptation in LMS color space
(responses of long-, medium-, and short-wavelength cone response space):
This diagonal matrix D maps cone responses, or colors, in one adaptation state to corresponding colors in another; when the adaptation state is presumed to be determined by the illuminant, this matrix is useful as an illuminant adaptation transform. The elements of the diagonal matrix D are the ratios of the cone responses (Long, Medium, Short) for the illuminant's white point
.
The more complete von Kries transform, for colors represented in XYZ
or RGB color space
, includes matrix transformations into and out of LMS space
, with the diagonal transform D in the middle.
Chromatic adaptation
Chromatic adaptation is one aspect of vision that may fool someone into observing a color-based optical illusion, such as the same color illusion.An object may be viewed under various conditions. For example, it may be illuminated by sunlight, the light of a fire, or a harsh electric light...
is one aspect of vision that may fool someone into observing a color-based optical illusion
Optical illusion
An optical illusion is characterized by visually perceived images that differ from objective reality. The information gathered by the eye is processed in the brain to give a perception that does not tally with a physical measurement of the stimulus source...
, such as the same color illusion
Same color illusion
The checker shadow illusion is an optical illusion published by Edward H. Adelson, Professor of Vision Science at MIT in 1995. The image depicts a checkerboard with light and dark squares. The optical illusion is that the area of the image labelled A appears to be a darker color than the area of...
.
An object may be viewed under various conditions. For example, it may be illuminated by sunlight, the light of a fire, or a harsh electric light. In all of these situations, human vision perceives that the object has the same color: an apple always appears red, whether viewed at night or during the day. On the other hand, a camera with no adjustment for light may register the apple as having varying color. This feature of the visual system is called chromatic adaptation, or color constancy
Color constancy
Color constancy is an example of subjective constancy and a feature of the human color perception system which ensures that the perceived color of objects remains relatively constant under varying illumination conditions. A green apple for instance looks green to us at midday, when the main...
; when the correction occurs in a camera it is referred to as white balance.
Though the human visual system generally does maintain constant perceived color under different lighting, there are situations where the relative brightness of two different stimuli will appear reversed at different illuminance
Illuminance
In photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of the intensity of the incident light, wavelength-weighted by the luminosity function to correlate with human brightness perception. Similarly, luminous emittance is the luminous flux per...
levels. For example, the bright yellow petals of flowers will appear dark compared to the green leaves in dim light while the opposite is true during the day. This is known as the Purkinje effect
Purkinje effect
The Purkinje effect is the tendency for the peak luminance sensitivity of the human eye to shift toward the blue end of the color spectrum at low illumination levels.This effect introduces a difference in color contrast under different levels of...
, and arises because the peak sensitivity of the human eye shifts toward the blue end of the spectrum at lower light levels.
Von Kries transform
The von Kries chromatic adaptation method is a technique that is sometimes used in camera image processing. The method is to apply a gain to each of the human cone cellCone cell
Cone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...
spectral sensitivity responses so as to keep the adapted appearance of the reference white constant. The application of Johannes von Kries
Johannes von Kries
Johannes Adolf von Kries was a German physiological psychologist who formulated the modern “duplicity” or “duplexity” theory of vision mediated by rod cells at low light levels and three types of cone cells at higher light levels...
's idea of adaptive gains on the three cone cell
Cone cell
Cone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...
types was first explicitly applied to the problem of color constancy by Herbert E. Ives
Herbert E. Ives
Herbert Eugene Ives was a scientist and engineer who headed the development of facsimile and television systems at AT&T in the first half of the twentieth century. He was also a critic of the special theory of relativity, and attempted to disprove the theory by means of logical arguments and...
, and the method is sometimes referred to as the Ives transform or the von Kries–Ives adaptation.
The von Kries coefficient rule rests on the assumption that color constancy
Color constancy
Color constancy is an example of subjective constancy and a feature of the human color perception system which ensures that the perceived color of objects remains relatively constant under varying illumination conditions. A green apple for instance looks green to us at midday, when the main...
is achieved by individually adapting the gains of the three cone responses, the gains depending on the sensory context, that is, the color history and surround. Thus, the cone responses
from two radiant spectra can be matched by appropriate choice of diagonal adaptation matrices D1 and D2:where
is the cone sensitivity matrix and is the spectrum of the conditioning stimulus. This leads to the von Kries transform for chromatic adaptation in LMS color spaceLMS Color Space
LMS is a color space represented by the response of the three types of cones of the human eye, named after their responsivity at long, medium and short wavelengths....
(responses of long-, medium-, and short-wavelength cone response space):
This diagonal matrix D maps cone responses, or colors, in one adaptation state to corresponding colors in another; when the adaptation state is presumed to be determined by the illuminant, this matrix is useful as an illuminant adaptation transform. The elements of the diagonal matrix D are the ratios of the cone responses (Long, Medium, Short) for the illuminant's white point
White point
A white point is a set of tristimulus values or chromaticity coordinates that serve to define the color "white" in image capture, encoding, or reproduction. Depending on the application, different definitions of white are needed to give acceptable results...
.
The more complete von Kries transform, for colors represented in XYZ
CIE 1931 color space
In the study of color perception, one of the first mathematically defined color spaces is the CIE 1931 XYZ color space, created by the International Commission on Illumination in 1931....
or RGB color space
RGB color space
An RGB color space is any additive color space based on the RGB color model. A particular RGB color space is defined by the three chromaticities of the red, green, and blue additive primaries, and can produce any chromaticity that is the triangle defined by those primary colors...
, includes matrix transformations into and out of LMS space
LMS Color Space
LMS is a color space represented by the response of the three types of cones of the human eye, named after their responsivity at long, medium and short wavelengths....
, with the diagonal transform D in the middle.