Color

Color Notation

1. Color of Light
Color mixing system ex: CIE

Picture 1

    The CIE system is an international method which was recommended in 1931 by the Commission Internationale de l'Eclairage. It use Tristimulus values to express all colors. Tristimulus values are imaginary three primary colors. Tristimulus have already been changed to from real primary colors, RGB, by mathematical method.

    The standard CIE coordinates have tristimulus values, X, Y, Z.We take ratios of X, Y, Z to get x, y, z and the sum of x, y ,z is 1.
    Thus, only two of x, y, z are needed. Usually, we describe chromaticity by noting x, y. But we still need one of X, Y, Z in order to calculate X , Y, Z. A CIE specification often use in terms of X, Y, Z, or Y, x, y.

    In Picture 1, P1, P2, P3 are the values of X, Y, Z. In order to calculate the values of x, y, z, we take a unit in three axes to get a plane A B C. Let us make a line from O to F, and line OF and plane ABC have the same point, N. The value of N in three axes is the value of x, y, z.

2. Color of Pigment

    When we observe color, we can evaluate it in several attributes. Hue refer to the name of the color, like red, yellow. Saturation is the attribute that describe the strength of the color or the vividness of hue. Brightness is attribute referring to a scale of dim to bright. These three attributes can be represented by a three-dimensional model, Picture 2.

Picture 2

ex: Munsell Color Notation

    The Munsell hue scale have five basic hues, red(R), yellow(Y), green(G), blue(B), and purple(P). There is a intermediate hue between the two adjacent hue, so there are five intermediate, YR, GY, BG, PB, and RP. In these ten hues, every hue has 10 divisions. The value scale contains ten levels from 0 (black) to 10(white). Chroma scales can contain up to 16 or more levels from the neutral gray of equivalent value.

Take 5R-6/3 for example,5R refer to the fifth division in R region, 6 indicates value, 3 indicates Chroma.