Color Image Processing

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Color Models, Color Space

• A color model is a specification of a coordinate system within which each color is represented by a single point.
• Hardware-oriented color models; e.g., color monitors and printers, RGB, CMY (cyan, magenta, yellow), CMYK (+black)
• Application-oriented color model; HSI (hue, saturation, intensity)

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RGB Color Model

• Each color appears in its primary spectral components of R, G, and B
• Based on a Cartesian coordinate system (cube)

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HSI Color Model

• RGB and similar others are not practical for human interpretation.
• Hue: a color attribute that describes a pure color.
• Saturation: a measure of the degree to which a pure color is diluted by white light.
• The HSI space is represented by a vertical intensity axis, the length (saturation) of a vector from the axis to a color point, and the angle (hue) this vector makes with the red axis.
• The power of HSI color model is to allow independent control over hue, saturation, and intensity.

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Converting colors from RGB to HSI

Converting colors from HSI to RGB

1. RG Sector (0 < H < 120):

2. GB Sector (120 < H < 240):

3. BR Sector (240 < H < 360):

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Normalization