Chapter 14
Color Models

• Primary colors: red, green, blue. These are the colors that eyes can sense.

• Other colors are interpretations given to mixtures of primary colors.

  White = red + green + blue

• Complementary colors

  Cyan	=	white	-	red	=	blue	+	green
  Yellow	=	white	-	blue	=	green	+	red
  Magenta	=	white	-	green	=	blue	+	red

14.1 RGB

• Color

• Device independent intensities [0, 1]

• The Line (0,0,0--(1,1,1) gives the full spectrum of gray levels.

• A CRT-oriented model: phosphorus emit red, green, and blue light.

Intensities

• Converted from normalized continuous spectrum [0..1] to desecrate values of graphical systems: I₀ = 0, I₁, ..., I_n.

• A change I_i I_i+1 is perceived to be the same as I_j I_j+1 if I_i+1 I_i = I_j+1 I_j .

• Let I_i = 2^i-1 /2^n-1 for i > 1

14.2 CMY: Cyan, Magenta, and Yellow

• Hard-copy oriented: pigments absorb light

14.3 HSU: Hue, Saturation, and Value

• Human-oriented

14.4 Dithering

• Increase choice of colors on account of resolution: reduce resolution by a factor of n and apply an n × n dither matrix at each coordinate.

• Example: dither matrices for n = 2 and 2 colors (white/black)

14.5 Halftoning

A generalization suitable to continuous display: gray level at a grid point determined by size of spot.