Second, three primary color models
Below we start specific explanation of color models.
As we all know, when we use two different colors to make another color, we can get the color we want by mixing three different colors, which is the basic principle of the three-base color model. But theory suggests that there is no combination that can generate all colors in the actual primary color group. Take the RGB us commonly used as an example, as shown below:
This is a color matching diagram, which represents the R, G, B ratio required to generate a spectrum color. From the figure, it can be seen in the optical wave color in 500 nm, and therefore, the RGB display cannot be Light wave colors near 500 nm.
XYZ color model
In order to define all the colors with three basins, the International Lighting Committee CIE defines three standard primary color XYZ. These three primary colors are imaginary colors and also give color matching diagrams (see on the right). Thus all the definitions of all colors have international standards, and we have XYZ color models.
Cr = AX by CZ
We let x = x / (x y z) y = y / (x y z), so x, y's value is only dependent on the color and purity of the light source, and is independent of the brightness of the light source, and we The parameters x, y is called chromaticity. We can determine all colors through chroma.
Through the chart of (x, y), we get the following picture, called CIE chromaticity chart.
The point on the curve is the spectral color, that is, pure color, the highest purity. Linendline of red and purple is called a purple line, which is not a spectral color. The point surrounded by the curve is all possible combinations of all possible visible light, and the C point is white, and it is obvious that the lower it close to the C point. As a result, all colors in nature are included in the area surrounded by the curve.
Have a color graph to help us:
First, compare the entire color range for different primary color groups. The color range determined by the primary color group is represented as a straight segment or polygon. As shown in Figures, C1, C2, C3 are the base color group we have chosen, then the triangle formed by the three points of C1, C2, and C3 is the color range determined by the primary color group, and all colors in the triangular shape can be mixed. C1, C2, C3 are obtained. Since there is no triangle in the figure contains all colors, this is why no three-base color group can generate all colors.
Second, identify complementary colors. If the light of the two colors can get white light after a certain proportion, then we call it complementary color. For example, red and cyan, blue and yellow. From the chromaticity map, complementary color must be at both ends of a line segment over white C point. As shown below, mixing the appropriate amount of C1, C2 can get white.
Third, determine the main frequency and purity of the selected color. We can determine the main frequency of a color through interpretation of the two-primary color range. As at the C1 point in the following figure, it is intersected from the C point C1 to the spectral curve, and we get a CS point so that the color C1 can be expressed as a color CS and white light mix. So the main frequency of C1 is CS. However, this method is not applicable to the color points between C and purple lines such as C2, because the purple line is not a spectral range. To this end, we made the reverse extension line of C2C, and the spectral curve is in the CP point, then the main frequency of C2 is CP, and the C2 is explained to obtain CP from white.
