Color vision distinguishes distributions of visible light across wavelengths through the different spectral sensitivities of visual receptors. A perceived colour need not correspond to one wavelength: different optical spectra can produce the same receptor responses. Consequently the broad spectral filtering of thin-film interference need not produce pure monochromatic colours.
Assigning linguistic labels to color stimuli or appearances. Shared naming, discrimination and matching must be measured separately; one observation does not define the others.
Measurement and specification of color-related stimulus relations, especially matches and coordinates for stated observers and conditions. Device values require spectral and radiometric calibration before they can be interpreted as cone stimulation.
Measurement and adjustment of a display's spectral, intensity and temporal output relative to control settings. The emitted primary spectra and their nonlinear control functions matter; RGB numbers alone do not specify retinal stimulation.
A stimulus manipulation designed to vary one receptor class while holding others approximately fixed. With a calibrated primary-to-receptor matrix , solve for primary changes producing a specified catch change, respecting baseline and gamut constraints. Observer variation, calibration error and unintended receptor inputs can limit isolation.
The set of stimuli or coordinates realizable by a specified device or system. If primary intensities are bounded and nonnegative and cone catches satisfy , invertibility of does not ensure feasibility: a requested can lie outside the permitted primary ranges.
Color information considered apart from an overall intensity coordinate under a stated colorimetric convention. It is distinct from accelerator chromaticity and should not be confused with a complete appearance description.
A coordinate representation of color stimuli or responses under stated conventions. Euclidean separation in a chosen space need not equal perceptual discriminability for every observer and task.
Relative stability of perceived surface color across changes in illumination or viewing conditions. The measured degree depends on task, adaptation and available cues. Perfect physical recovery is impossible in unrestricted scenes because illumination and reflectance can be nonunique.
In a diffuse spectral model , choose any positive for which remains an admissible reflectance. Then and preserve exactly. Thus outgoing spectral information alone does not uniquely identify reflectance and illumination; three-channel receptor sampling introduces further ambiguity.
The experienced color of a stimulus under specified viewing, adaptation and contextual conditions. Appearance judgments, discrimination thresholds and naming are related but different observations.
A stimulus setting judged to have no chromatic tint under stated conditions. An observer adjusting a patch to cancel a perceived tint moves the physical setting in a compensating direction; the adjustment must not be confused with the direction of the original appearance shift.
Perceived surface achromatic reflectance, often judged relative to a white reference. The same outgoing luminance can support different lightness interpretations under different illumination or scene context.
Perceived amount or intensity of light from a stimulus. It is distinct from physical luminance and from lightness as a judgment related to surface reflectance.
The color attribute distinguishing appearances such as red, yellow, green or blue and their combinations. A hue need not identify a single wavelength, and cone-class labels do not directly specify it.
A hue judged to contain no perceptual mixture of a specified opponent pair, such as a yellow judged neither reddish nor greenish. Its measured setting depends on observer and conditions and should not simply be identified with one retinal cardinal axis.
A yellow judged neither reddish nor greenish. A wavelength or matching setting can operationalize the judgment under controlled conditions; shifts in that setting do not by themselves identify the neural locus of a change.
A receptor catch change expressed relative to a positive adapted-background catch. The same absolute increment can represent different contrasts on different backgrounds. These coordinates are useful for isolating signals without asserting that all neurons explicitly divide in this way.
A class of post-receptoral computations comparing signals from different cone populations, for example a gain-weighted L–M difference and an S versus L+M comparison. Such comparisons distinguish spectral differences from shared changes in illumination intensity. Receptor counts, signal gains and later appearance judgments need not vary proportionally.
Stimulus directions distinguished by selective adaptation or physiological response nulls under specified conditions, commonly associated with an achromatic-like combination and two cone-opponent combinations. Their usefulness near a particular background does not make them identical to unique-hue directions or sufficient for every suprathreshold appearance judgment.
If a nonzero weight vector combines cone contrasts as , its zero-response contrasts satisfy one linear constraint and form a two-dimensional plane through the adapted origin in three-dimensional contrast space. Any two independent vectors in that plane constrain the direction of the normal , up to scale. Nonlinearities and response noise limit empirical identification.
The illustrative transform , , has determinant . Solving gives , and . Thus it reorganizes three cone coordinates without adding independent spectral information. Biological response weights and nonlinearities are further empirical questions.
The ability to distinguish stimuli using their chromatic differences under stated conditions. Controlled tests suppress luminance and other unintended cues and estimate a psychometric function. Color matching, color naming and discrimination are different observations.
Color vision using four functionally independent spectral channels. Four pigment variants or four potential cone cell types do not alone demonstrate four-dimensional behavioral discrimination. Tests must establish information use beyond the matches available to a specified trichromat.[ref]
An observer adjusts lights until they appear to match a comparison under specified viewing and adaptation conditions. The settings and range of accepted matches constrain the available spectral signals. Matching differs from detecting a difference and from assigning a color name.
A match between a mixture of two long/middle-wave lights and a comparison light, with mixture ratio and brightness separately adjustable. The settings and acceptance range help characterize red–green color-vision variation. A satisfactory brightness match alone is not evidence for normal chromatic discrimination.
A model relating a stimulus to the inputs and discrimination capacity of a visual system. Receiver spectral sensitivity, illumination and background matter; human colour distances are not automatically perceptual distances for another animal.
Variability in a sensory receptor signal that limits discrimination. A difference in average receptor quantum catch does not alone establish a perceptually discriminable difference.
Expected photon absorption by a receptor class. A simple relative model is , with illumination , object reflectance and effective spectral sensitivity . Absolute catch also requires geometric and temporal factors.
Dichromacy is color vision based on two functionally independent classes of photoreceptor input. Their different spectral sensitivities permit some optical spectra to be distinguished, but distinct spectra can still produce identical pairs of receptor responses and hence be metamers under the stated conditions.
A color matching experiment asks an observer to adjust primary lights to match a comparison field while controlling luminance cues. The available matches constrain the independent spectral information used by that observer. Two receptor classes do not mean that every appearance can be identified with one of only two named colors.
Colour vision based on three classes of photoreceptor input. Functional discrimination must be tested rather than inferred solely from gene count.
Color vision with three independent receptor classes whose spectral sensitivities differ from a reference trichromat's, often reducing separation of long- and middle-wave signals. A shifted sensitivity, fewer receptors and loss of an entire independent class are different mechanisms and should not be conflated.
Color is a perceptual attribute arising from the optical spectrum reaching an observer and the observer's visual processing and viewing conditions. Cone cells have overlapping spectral sensitivities, so their responses do not provide a separate measurement of every wavelength. Different optical spectra can therefore produce the same color match, an instance of metamerism.
For a transmitting sample, the incident optical spectrum is modified by wavelength-dependent transmittance. Removing part of the blue band can make the remaining light appear yellow, but the absorption maximum alone does not specify the resulting shade. Changing the illuminant or background can change color appearance without changing the sample.
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Color vision is the capacity of the visual system to perceive and distinguish different colors. This ability arises from the way the human eye and brain process light. The retina, located at the back of the eye, contains photoreceptor cells known as cones, which are responsible for color detection. There are three types of cones, each sensitive to different wavelengths of light corresponding to red, green, and blue colors.