Color is a feeling of the human eye, which can be divided into two categories: colorless and colored, of which colorless only has the lightness attribute, while color has three attributes: brightness, hue and saturation. In order to digitally express color, people combine hue, brightness, and color saturation to form different color spaces. This article introduces the basic concept of color and the numerical representation method of color, and friends who are interested in it can learn about it!
Color is a human feeling. When light hits a non-light source object, except for a small part that is reflected off the surface of the object, most of the light enters the object and is selectively absorbed, and the unabsorbed part escapes (reflected or transmitted) from the object, and when the observer receives the reflected (or transmitted) light, the color of the object is determined by this part of the spectral distribution. Factors that affect the perception of color are: light source, object being observed, eyes, and brain. Because color is a human sense, even if you look at the same object, it may look different under different conditions.
Colors can be divided into two categories: achromatic and achromatic, and achromatic is also known as achromatic. For example, black, white, gray, etc. are all achromatic, and other colors such as red, orange, yellow, green, blue, etc. are all colors. Colors are represented by 3 basic properties:
1) Hue, also known as hue, indicates the classification of colors, such as red, orange, yellow, green, blue, etc. The hue of spectral colors is determined by the wavelength of light, and the various colors are determined by the spectral distribution.
2) Brightness, which indicates the brightness of the surface color of the object, which is equivalent to the brightness in the color of the light source. When the object absorbs less light and reflects more light, it looks bright, and the brightness appears as a level from black to white, and the brightness is higher when it is close to white.
3) Color saturation, also known as purity or saturation, indicates the strength of the color itself, in the color of a certain hue, the less achromatic components, the higher the color saturation.
People put the three attributes of hue, brightness, and color saturation together to form a three-dimensional three-dimensional. In a three-dimensional stereograph, hue forms the outer edge of the stereotype, with brightness as the main axis and color saturation as the horizontal banner. However, due to the fact that the size of each step of color saturation is unequal for each hue and brightness, the shape of the color stereo is very complex, but the relationship between hue, brightness and color saturation can be expressed in an intuitive way, which constitutes the basic concept of a color space and makes it possible to digitally represent color. On this basis, the International Commission on Illumination (CIE) has studied and developed a multi-color spatial digital representation. Among them, the YXY color space method and the l*a*b* color space method are the most commonly used representation methods.
The concept of XYZ tristimulus is based on the triadic theory of color vision, which states that the human eye has receptors for accepting the three primary colors (red, green, and blue), and that all colors are considered to be a mixture of the three primary colors. In 1931 the CIE developed a hypothetical standard observer with a color matching function x( )y as shown in the figure above
, and z( )xyz tristimulus values are calculated using these standard observer color matching functions. On this basis, CIE defined the YXY color space in 1931, where Y is the luminance and X,Y is the color coordinates calculated from the tristimulus value XYZ, and the following figure shows the CLEX and Y chromaticity diagrams of this color space. The chromaticity diagram is the vanishing area in **, and the chromaticity becomes stronger towards the edges.
The l*a*b* color space was formulated in 1976 in order to overcome the problem that the original yxy color space existed that the equal distances on the x,y chromaticity diagram were not equivalent to the equal chromatic aberration that we perceived. In this color space, l* is the brightness and a* and b* are the color coordinates. This is shown in the figure below.
In the diagram, +a* is the red direction, -a* is the green direction, +b* is the yellow direction, and -b* is the blue direction. ** is the achromatic zone, when the a* and b* values increase, the color point is far away from the center, and the color saturation increases. When comparing color differences, it can be expressed as the Euclidean distance between two color swatches. The straight-line distance between two points of two sensory colors is determined by the following formula:
The size of e*ab determines the degree of chromatic aberration, and the relationship between it and the degree of sensation between it and the human eye is as follows:
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