Color Image Processing

1. Color Fundamentals

Definition and Nature of color:

• color is the visual perception resulting from light in the visible spectrum (wavelengths between 380 nm to 780 nm) hitting the retina. The brain interprets electric impulses from the retina to generate the sensation of color.
• Light behaves as both a particle (photon) and a wave (electromagnetic).

Visible Spectrum and Light Types:

• Chromatic Light: Contains color; spans 400 nm to 700 nm.
• Achromatic Light: Intensity-only light; appears as black, white, and gray tones.

Physical Properties of Light:

1. Radiance: Total energy emitted by a source, measured in watts (W).
2. Luminance: Perceived brightness, measured in lumens (lm).
3. Brightness: A subjective measure; represents intensity and visual sensation.

Human color Perception:

• The retina contains cones sensitive to color:
  • Red-sensitive cones: ~65% of total.
  • Green-sensitive cones: ~33%.
  • Blue-sensitive cones: ~2% (though most sensitive).
• Primary colors: Red (R), Green (G), and Blue (B).
• Secondary colors: Cyan (G+B), Magenta (R+B), Yellow (R+G).

A primary color is defined as one that subtracts or absorbs a primary color of light and transmits the other two.

Primary colors of pigments are magenta, cyan, and yellow

the secondary colors are red, green, and blue.

A proper combination of the three pigment primaries, or a secondary with its opposite primary, produces black

Characteristics of color: