Fundamentals of Color Images

 Definition of color:

 Light is a form of electromagnetic (em) energy that can be completely specified at a point in the image plane by its wavelength distribution. Not all electromagnetic radiation is visible to the human eye. In fact, the entire visible portion of the radiation is only within the narrow wavelength band of 380 to 780 nms. Till now, we were concerned mostly with light intensity, i.e. the sensation of brightness produced by the aggregate of wavelengths. However light of many wavelengths also produces another important visual sensation called “color”. Different spectral distributions generally, but not necessarily, have different perceived color. Thus color is that aspect of visible radiant energy by which an observer may distinguish between different spectral compositions.

 A color stimulus therefore specified by visible radiant energy of a given intensity and spectral composition.Color is generally characterised by attaching names to the different stimuli e.g. white, gray, back red, green, blue. Color stimuli are generally more pleasing to eye than “black and stimuli” .Consequently pictures with color are widespread in TV photography  and  printing.

 Color is also used in computer graphics to add “spice” to the synthesized pictures. Coloring of black and white pictures by transforming intensities into colors (called pseudo colors) has been extensively used by artist's working in pattern recognition. In this module we will be concerned with questions of how to specify color and how to reproduce it. Color specification consists of 3 parts:

 (1) Color matching

 (2) Color differences

 (3) Color appearance or perceived color

 We will discuss the first of these questions in  this module