Color

Light Spectrum

• Visible light comes in different wavelengths (or frequencies).

• Each wavelength represents a color.• Red (~700-630nm), Green(~560-490nm), Blue

(~490-450nm).

Human Vision

• The retina in human eyes has three color receptor cells, or cones.

RGB

• RGB is an additive color model.• The primary colors are added to

produce new colors.

RGB• Numeric Representation

– (0, 0, 0) is black– (255, 255, 255) is white– (255, 0, 0) is red– (0, 255, 0) is green– (0, 0, 255) is blue– (255, 255, 0) is yellow– (0, 255, 255) is cyan– (255, 0, 255) is magenta– (255,255,0) green– (0,255,0) cyan– (0,255,255) red

Geometric Representation

Normalization

• Intensity I = (R + G + B)/3.• Normalized Red

r = R/(R + G + B).• Normalized Green

g = G/(R + G + B).• Normalized Blue

b = B/(R + G + B).

HSI Color Model

• HSI = Hue, Saturation and Intensity.

RGB to HSI Conversion

• To find the hue angle h [0, 360]∈

HSI to RGB Conversion

• HSI to RGB