1.1. Definition of "L, a, b"
During the 1950s-1960s, Hunter Lab established a color space, represented by Lab three-dimensional coordinates
"L" represents the lightness of the object: 0-100 means from black to white
"a" represents the red-green color of the object: positive values represent red, negative values represent green
"b" represents the yellow-blue color of the object: positive values represent yellow, negative values represent blue
1.2．The significance of establishing the "Lab" color space
The "Lab" color space forms a unified color, color description language and operation specification. The "Lab" color space is one of the commonly used spaces for measuring the color of objects, and it is widely used in most fields. Use Lab to express the reflected color or transmitted color of the physical sample. Unlike RGB and CMYK color spaces, Lab color is designed to approximate human vision, which strives for perceptual uniformity, and its L component closely matches human perception of lightness.
2.1 Definition of "L" "C" "h"
In the figure, "HUE" is represented by "h" for hue, and "CHROMA" is represented by "C" for chroma. "L" stands for lightness, "C" is chroma, that is, the degree of color saturation, and "h" is hue, that is, the overall tendency of color. "L", "C" and "h" are the three elements of color.
2.2. Establish the meaning of "L", "C" and "h"
Brightness is the eye's perception of the light and dark degree of the light source and the surface of the object. The lightness not only determines the degree of illumination of the object, but also determines the reflection coefficient of the surface of the object.
Saturation (chroma, vividness) usually refers to the vividness of a color. From a scientific point of view, the vibrancy of a color depends on how monotonously the hue emits light.
The characteristics of the color tone are determined by the spectral composition of the light source and the ratio of the radiation of each wavelength reflected by the surface of the colored object to the perception of the human eye. It is the qualitative appearance that color can present, and it is the accurate standard for distinguishing various colors. In many cases, we generally use the (Lab) color space to describe the color, but in some cases, such as brightness and saturation, but the hue changes, we generally use L ch to describe the color. For example, the classification of raisin color, measuring the color change of honey and so on.
