CS321 Dr' Mark L' Hornick

1
Color Perception
2
Color Perception
3
Color Spectrum
Red
Violet
750 THz
430 THz
400 nm
700 nm
4
Additive colors
5
(No Transcript)
6
The Human Eye

• The photosensitive part of the eye is called the
  retina.
• The retina is largely composed of two types of
  cells, called rods and cones. Only the cones are
  responsible for color perception.

7
The Fovea
8

• There are three types of cones, referred to as S,
  M, and L. They are roughly equivalent to blue,
  green, and red sensors, respectively. Their peak
  sensitivities are located at approximately 430nm,
  560nm, and 610nm for the "average" observer.
• Colorblindness results from a deficiency of one
  cone type.

9
RGB Color matching functions
10
Color Perception

• Different spectra can result in a perceptually
  identical color sensations called metamers
• Color perception results from the simultaneous
  stimulation of 3 cone types (trichromat)
• Our perception of color is also affected by
  surround effects and adaptation
• Different spectral distributions that look the
  same
• Infinitely many metamers produce the same
  perceived color

11
Primary Colors

• Set of colors
• E.g., phosphor colors
• Combined to produce colors
• Within a specified gamut
• Cant produce all visible colors
• Good enough approximation for most cases

12
CIE

• Commission Internationale de lÉclairage
• International Commission on Illumination
• 1931
• Color primaries
• Imaginary colors
• Chromaticity diagram

13
CIE Color Primaries
Color-matching functions Mix x,y,z
primaries Match any visible color
14
CIE Chromaticity Diagram
15
CIE Diagram Details
Spectral colors around curve
Line of purples
White reference (C)
SIGGRAPH 1995 Educators Slides
16
Color Gamut
Line between color points indicates mixing
results.
Polygon (triangle) connecting primaries delimits
gamut.
17
Color Models (1)

• RGB red,green,blue
• YIQ luminance, chrominance
• Y luminance, 4 MHz
• I orange-cyan, 1.5 MHz
• Q green-magenta, 0.6 MHz
• CMY cyan, magenta, yellow
• Subtractive primaries (CMYK?)

18
Subtractive colors
19
Color Models (2)

• HSV hue, saturation, value
• Hue color
• Saturation purity of color
• Value black to white
• HLS hue, lightness, saturation