Basic Color Spaces  (Part 1)

         Hue, lightness, and saturation. These tree elements are the three color attributes, and can be put together to creatre the three dimensional solid shown in Figure 1 would be created. The shape of the color soild is somewhat complicated because the size of the steps for saturation are different for each hue and lightness, but the color solid helps us to better visualize the relationship between hue, lightness, and saturation.

          Other methods for expressing color numerically were developed by an international organization concerned with light and color, the Commission Internationale de I’Eclairage (CIE). The two most widely known of these methods are the Yxy color space, devised in 1931 based on the tristimulus values XYZ defined by CIE, and the L*a*b* color space, devised in 1976 to provide more uniform color differences in relation to visual differences. After various improvements, color spaces* such as these are now used throughout the eorld for color communication.

        Figure 1   (Color-Matching Functions/1931 Standard Observer)                                 Figure 2 Diagram x,y ปี 1931

XYZ Color space

     XYZ tristimulus values and the associated Yxy color space from the foundation of present CIE color spaces. The concept for the XYZ tristimulus values is based on the three-component theoty of color vision, which states that the eye possesses receptors for three primary colors (red,green, and blue) and that all colors are seen as mixtures of these three primary colors. The CIE in 1931 defined the Standard Observer to have the color-matching function, x(λ),y(λ) and Z(λ) show in Figure 1 below. The XYZ Tristimulus values are calculated using these Standard Observer color-matching functions.

      The Tristimulus values XYZ are useful for defining a color, but the result are not easily visualized. Because of this, the CIE also defined a color space in 1931 for graphing color in two dimensions independent of lightness; this is the Yxy color space, in which Y is the lightness (and is identical to Tristimulus values Y) and x and y are the chromaticity coordinates calculated from the Tristimulus values XYZ The CIE x,y chromaticity diagram for this color space is shown in Figure 2

In this diagram, achromatic colors are toward the center of the diagram, and the chromaticity increases toward the edges.

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