Computer Graphics

1
Computer Graphics

• Color Models

2
What is a Color Model?

• A method for representing colors
• Each color is normally represented by a triple
• Color models include
• CIE
• RGB
• YIQ
• CMY
• HLS
• HSV

3
Some terms ...

• complimentary colorstwo colors that make white
  light
• primary colorsbasic set of 3 colors for a model
• color gamutrange of colors derived from models
  primary colors

• dominant frequency (or wavelength)hue
• brightnessintensity of a color
• saturationpurity of a color
• chromaticitypurity and dominant frequency
  combined

4
How do we see color?

• In the eye
• Rods sense the intensity light at low intensities
• Cones sense the intensity of light at moderate to
  high levels
• Cones exist for red, green and blue light

5
CIE

• Commission Internationale de lEclairage
• C? XX YY ZZ
• x X / (XYZ)y Y / (XYZ)z Z /
  (XYZ)xyz 1
• (x,y) are the chromaticity coordinates (values)

6
CIE
7
RGB

• C? rR gG bB

8
YIQ

• Used in composite video(National Television
  System Committee - NTSC)
• Y (luminance)I (orange-cyan hue)Q
  (green-magenta hue)

9
CMY

• Cyan, Magenta, Yellow
• Subtractive color model
• Used in printing

10
HSV
V

• Hue
• Saturation
• Value

Green 120?
V1(White)
Red 0?
Blue 240?
H
S
11
HLS
L 1

• Hue
• Lightness
• Saturation

Green 120?
L 0.5
Red 0?
Blue 240?
H
L 0
S