Color spaces

Figure 6.21: One representation of the HSV color space, which involves three parameters: hue, saturation, and value (brightness). (Figure by Wikipedia user SharkD.)

Figure 6.22: 1931 CIE color standard with RGB triangle. This representation is correct in terms of distances between perceived colors. (Figure by Jeff Yurek, Nanosys.)

For convenience, a parameterized color space is often defined. One of the most common in computer graphics is called HSV, which has the following three components (Figure 6.21):

• The hue, which corresponds directly to the perceived color, such as ``red'' or ``green''.
• The saturation, which is the purity of the color. In other words, how much energy is coming from wavelengths other than the wavelength of the hue?
• The value, which corresponds to the brightness.

There are many methods to scale the HSV coordinates, which distort the color space in various ways. The RGB values could alternatively be used, but are sometimes more difficult for people to interpret.

It would be ideal to have a representation in which the distance between two points corresponds to the amount of perceptual difference. In other words, as two points are further apart, our ability to distinguish them is increased. The distance should correspond directly to the amount of distinguishability. Vision scientists designed a representation to achieve this, resulting in the 1931 CIE color standard shown in Figure 6.22. Thus, the CIE is considered to be undistorted from a perceptual perspective. It is only two-dimensional because it disregards the brightness component, which is independent of color perception according to color matching experiments [206].