I have already talked about the basic knowledge of light source and object color. The theme of this article is the color knowledge of the human eye, which is the human eye in the three elements of color.
Photoreceptor cells on the retina
The structure of the human eye is as follows, including the cornea, iris, pupil, lens, vitreous, retina, and the like. There are three kinds of pyramidal cells and one kind of rod-shaped cells in the eyeball of normal vision. The cone cells are mainly located in the fovea of ​​the retina (Retina), and the three cone-like cells induce short-wave (blue), medium-wave (green) and long-wave (red) portions, respectively, corresponding to visible spectra from 400 nm to 700 nm. Scope, mainly responsible for the color and detail perception under bright conditions, that is, Photopic Vision, whose cell number distribution ratio is approximately 1:16:32, which is one of the reasons why the Blu-ray human eyes perceive low brightness; Rod cells sense brightness information only under low-light conditions, can't distinguish color and detail, so it is Scotopic vision; between middle and dark vision, Mesopic vision is currently studied. Hot spots, because cone cells and rod cells work at the same time, the brightness range is generally 0.001-5cd/m2; the research of intermediate vision has important guiding effects on street lamp design and outdoor lighting. The color perception and color judgments described in our color industry are generally referred to as bright visual conditions, that is, mainly three types of pyramidal cells function.
In 2002, Bersons and others at Brown University in the United States discovered a new kind of photoreceptor cells, namely intrinsically photosensitive ganglion cells (ipRGC), but this cell does not participate in color vision. ipRGC controls the secretion of melanopsin, which is involved in the circadian rhythm and sleep quality. For details, please refer to this public article "Guang Ya Exhibition, talk about the light source related to the spectrum."
Human eye structure
Red, green and blue photoreceptor cell distribution map on the retina
Spectral response curves of short-wave (420), medium-wave (534), long-wave (564) cones and rod-like (Rod) spectral response curves
When a person's pyramidal cells are not sensitive or problematic, it is a phenomenon of so-called color weakness or color blindness. Tested by using the Ishihara Test color blind test.
IshiharaTest color blind test chart
Normal visual observer
Visual observer lacking long-wave cone cell induction
Spectral luminous efficiency represents the brightness perception characteristics of the human eye to light of different wavelengths. It can be seen from the figure that the spectral light efficiency functions V(λ) and V'(λ) are different under bright and dark vision, and the human eye is most sensitive to yellow-green light at 555 nm in the case of bright vision. At present, all illuminance or brightness measuring devices use V(λ) for calculation. It should be pointed out that the photoreceptor cell and spectral luminous efficiency functions for each individual are different, and the individual is different.
Bright visual and dark visual spectral light efficiency function
In addition to humans, other animals also have corresponding photoreceptor cells, and different from human photoreceptor cell response curves, such as whales have only one photoreceptor cell, dog and cat have two photoreceptor cells, bees have three photoreceptor cells, and birds have four photoreceptor cells. There are 12 kinds of photoreceptor cells in Shrimp.
Different animal photoreceptor cell types
Spectral response curve of human and bee photoreceptor cells
Spectral response curve of photoreceptor cells in birds and shrimp
Color adaptation and color constancy
First look at the very classic three pictures in the color science below. The first one is a normal complete picture; the second one is only covered with a cyan filter on the yellow pillow, and the yellow pillow is obviously colored; the third picture The whole picture is covered with a cyan filter. After a period of adaptation, the overall feeling is yellow or yellow. Similarly, a piece of white paper was taken under the incandescent light from daylight. At first, the white paper was yellowish and reddish. After a period of color adaptation, the white paper felt white paper. These phenomena are the color adaptation and color constancy of the human eye. Color constancy is such that when the lighting conditions change, although the overall color perception will always be somewhat different, the human visual system has a tendency to minimize the difference in perceived color. At present, CIE has introduced a corresponding mathematical model to accurately describe this process, namely CAT02 color adaptive conversion and CIECAM02 color appearance model, which will be discussed later. The essence of color constancy is consistent with the white balance of the camera. The white balance algorithm is essentially a color compensation algorithm that compensates for the camera's inability to automatically adapt to various scene lighting for color adjustment.
Normal complete picture
Part of the yellow pillow is covered by a cyan filter
The full picture is covered by a cyan filter
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