Color Image Processing

.Three basic quantities are used to describe the quality of a chromatic light source:

• Radiance - total amount of energy that flows from the light source, and it is usually measured in watts (W).
• Luminance - measured in lumens (lm), gives a measure of the amount of energy and observer perceives from a light source.
• Brightness - is a subjective descriptor that is practically impossible to measure. It embodies the achromatic notion of intensity and is one of the key factors in describing color sensation.

Example: light emitted from a source operating in the far infrared region of the spectrum could have significant energy (radiance), but an observer would hardly perceive it; its luminance would be almost zero.

Sensors in human eyes for color vision: cones -

• Red - 65%
• Green - 33%
• Blue - 2%

--> CIE designated the following wavelength to the three primary colors:

• 435.8nm - blue
• 546.1nm - green
• 700.0nm - red

* If refer to the color spectrum, NO SINGLE color (wavelength) can be called red, green or blue.
** Having three specific primary color wavelengths for the purpose of standardization does not mean that these three fixed RGB components acting alone can generate all spectrum colors.
*** Misinterpretation of PRIMARY color = three standard primaries, when mixed in various intensity proportions, can produce all visible color.


Secondary colors:

• Magenta (red + blue)
• Cyan (green + blue)
• Yellow (red + green)

Ref: Gonzalez, R. C. and Woods, R. E. Digital Image Processing 3rd Edition (Chapter 6: Color Image Processing), Ner Jersey: Pearson Education, 2008