What is CIE1931?

Since the childhood, when we talk about the colour, we have to refe to the concept of threegezerand three primary colors. we can see that, colour is a 3 D function, so it should be said as the three dimensional space. As shown in figure 1, it is the color spindle that is commonly used by the traditional colorimetric works to represent the colour, figure 2 is the 3 D color stereo designed according to the people’s ability of distinguishing the colour. Because of the limit of human thinking ability and performance ability, the 3 D coordinate system exposed serious limitations in practical application.

The display monitor adopts nitikaset law principle. Photoperiod of primary colors are red, green, blue In 1931, the international standard lighting committee (CIE) requires that the wavelengths of the three kinds of color are:

The red light（R）：700nm
The green light（G）：546.1nm
The blue light（B）：435.8nm

Each primary colour in nature can be formed by the mixture of the three primary colours according to a certain proportion.

On the basis of the above definition, people defined a group formula:

r=R/（R+G+B） g=G/（R+G+B）　b=B/（R+G+B）

Because r + g + b = 1, only the value of r and g are given, can a color is determined. In this way, all the color spectrum can be said in a two-dimensional graphic. Thus 1931 CIE-RGB table color system was established.

But, in the above formula, the value of r and g will be negative. Because in fact no negative light intensity exists, and this calculation is very inconvent and not easy to understand, people want to find another group of primary colors to replace CIE-RGB systems, so in 1931 CIE organization established three imaginary standard primary colors (red), Y (green), Z (blue), so that we can get he three values of the color matching function are positive value, and the expression way of X, Y, Z is still a similar formula. From this, 1931 CIE-XYZ system is devided. This system is the practical application of colorimetric tools, almost all measurement, standard and other aspects of the extensions related to colors are based on the starting point, it is therefore the emollient tool of color vision research.

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