The science of color and color vision

A survey of color science and color vision

Colour constancy in dichromats and trichromats: dependence on task

An important topic in the field of colour vision is the impact of colour vision deficiencies on daily life tasks. Investigating the extent to which colour constancy (i.e. the ability to recognise surface colour under different illuminants) is preserved in colour vision- deficient observers can provide us with insight into the nature and function of trichromatic colour vision. The first chapter of this thesis provides a summary of the very basics of colour vision, colour vision deficiencies, as well as colour constancy. Studies conducted on the colour constancy abilities of colour-vision-deficient observers versus those with normal colour vision are reviewed. The second chapter presents and reports the aims and methods of the proposed experiment (which could not take place due to the COVID-19 pandemic). This experiment investigated the colour constancy abilities of trichromats versus dichromats using two different colour constancy tasks (2D achromatic adjustment vs. 3D blocks-copying/selection task) and aimed to show how colour constancy depends on observer type as well as task type. The third chapter comprises of a computerised simulation. This simulation aimed to model the colour constancy of “ideal” observers when presented with various surfaces and illuminants. These observers involve simulated normal trichromats, anomalous trichromats and dichromats. A variety of yellow, blue, green and red illuminant shifts (from neutral daylight) were used, and surface chromaticity and observer types were compared. Overall, whilst no three-way interaction between illuminant shift, surface chromaticity and observer type were found in the simulation, strong main effects were found. It is suggested that a combination of simulated and experimental research is needed to understand the colour constancy mechanisms underpinning dichromacy and trichromacy at multiple levels (cone-based, cognitive and computational)

Comparing Colour Camera Sensors Using Metamer Mismatch Indices

A new method of evaluating the colorimetric accuracy of a color camera is proposed that is based on the size (appropriately normalized) of the metamer mismatch volume induced by a change of \u27observer\u27 from camera to human eye and vice-versa. The degree of metamer mismatching indicates the range in the discrepancy of the colour signals that can arise and as such is a more well-founded measure of colorimetric accuracy than traditional spectral-based measures such as the root mean squared difference in fit between the camera and eye\u27s sensitivity functions

The synthesis and analysis of color images

A method is described for performing the synthesis and analysis of digital color images. The method is based on two principles. First, image data are represented with respect to the separate physical factors, surface reflectance and the spectral power distribution of the ambient light, that give rise to the perceived color of an object. Second, the encoding is made efficient by using a basis expansion for the surface spectral reflectance and spectral power distribution of the ambient light that takes advantage of the high degree of correlation across the visible wavelengths normally found in such functions. Within this framework, the same basic methods can be used to synthesize image data for color display monitors and printed materials, and to analyze image data into estimates of the spectral power distribution and surface spectral reflectances. The method can be applied to a variety of tasks. Examples of applications include the color balancing of color images, and the identification of material surface spectral reflectance when the lighting cannot be completely controlled

The time-course of colour vision

Four experiments are presented, each investigating temporal properties of colour vision processing in human observers. The first experiment replicates and extends an experiment by Stromeyer et al. (1991). We look for a phase difference between combined temporal modulations in orthogonal directions in colour space, which might null the often-claimed latency of signals originating from the short-wavelength sensitive cones (S-cones). We provide another estimate of the magnitude of this latency, and give evidence to suggest that it originates early in the chromatic pathway, before signals from S-cones are combined with those that receive opposed L- and M-cone input. In the second experiment we adapt observers to two stimuli that are matched in the mean and amplitude of modulation they offer to the cone classes and to the cardinal opponent mechanisms, but that differ in chromatic appearance, and hence their modulation of later colour mechanisms. Chromatic discrimination thresholds after adaptation to these two stimuli differ along intermediate directions in colour space, and we argue that these differences reveal the adaptation response of central colour mechanisms. In the third experiment we demonstrate similar adaptation using the same stimuli, measured with reaction times rather than thresholds. In the final experiment, we measure the degree to which colour constancy is achieved as a function of time in a simulated stimulus environment in which the illuminant changes periodically. We find that perfect constancy is not achieved instantaneously after an illuminant chromaticity shift and that constancy of colour appearance judgements increases over several seconds

Detection of fruit and the selection of primate visual pigments for color vision

Primates have X chromosome genes for cone photopigments with sensitivity maxima from 535 to 562 nm. Old World monkeys and apes (catarrhines) and the New World (platyrrhine) genus Alouatta have separate genes for 535-nm (medium wavelength; M) and 562-nm (long wavelength; L) pigments. These pigments, together with a 425-nm (short wavelength) pigment, permit trichromatic color vision. Other platyrrhines and prosimians have a single X chromosome gene but often with alleles for two or three M/L photopigments. Consequently, heterozygote females are trichromats, but males and homozygote females are dichromats. The criteria that affect the evolution of M/L alleles and maintain genetic polymorphism remain a puzzle, but selection for finding food may be important. We compare different types of color vision for detecting more than 100 plant species consumed by tamarins (Saguinus spp.) in Peru. There is evidence that both frequency-dependent selection on homozygotes and heterozygote advantage favor M/L polymorphism and that trichromatic color vision is most advantageous in dim light. Also, whereas the 562-nm allele is present in all species, the occurrence of 535- to 556-nm alleles varies between species. This variation probably arises because trichromatic color vision favors widely separated pigments and equal frequencies of 535/543- and 562-nm alleles, whereas in dichromats, long-wavelength pigment alleles are fitter