Color and color models

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Information about Color and color models

Published on March 31, 2014

Author: HASHMI007



Color and color models


What is color ?  Color is a sensation produced by the human eye and nervous system.  It is useful to represent a color by a set of exactly three numbers.

Color is Human Sensation  Cone and rod receptors in the retina  Rod receptor is mostly for luminance perception  3 different types of cone receptors in the fovea of retina, responsible for color representation. Each type is sensitive to different wavelengths

Color model  A color model is an orderly system for creating a whole range of colors from a small set of primary colors.

Types of Color model  Subtractive Color  Additive Color  Additive color models use light to display color  subtractive models use printing inks.

The Two Most Common Color Models  RGB model  For computer  CMYK model  For printing  YCbCr model

RGB Color Model:  Additive color model.  For computer displays.  Uses light to display color.  Colors result from transmitted light.  Red + Green + Blue = White.

 The RGB Color Model  If R,G, and B are represented with 8 bits (24-bit RGB  image), the total number of colors is (28 )3=16,777,216

CMYK Color Model  Subtractive color model.  For printed material.  Uses ink to display color.  Colors result from reflected light.  Cyan + Magenta + Yellow = Black  Used internally in color printers  Complementary to RGB:  C=1-R  M=1-G  Y=1-B

Color Models  the color model RGB is used in hardware applications like PC monitors, cameras and scanners, the CMY color model is used in color printers,  Each color can be a point in the RGB color model cube. Red, green and blue are known as the primary colors. These colors can be added to produce secondary colors which are:  magenta = red + blue  cyan = green +blue  yellow = red + green  Other possible combinations:  white = blue (primary) + yellow (secondary)  white = green (primary) + magenta (secondary)  white = red (primary) + cyan (secondary)

Additive vs. Subtractive Color Models  Since additive color models display color as a result of light being transmitted (added) the total absence of light would be perceived as black. Subtractive color models display color as a result of light being absorbed (subtracted) by the printing inks. As more ink is added, less and less light is reflected. Where there is a total absence of ink the resulting light being reflected (from a white surface) would be perceived as white.

HSL and HSB  Hue Hue is what most people think of when we say "color".  Saturation Saturation is the "purity" of the color. It refers to the amount of gray paint mixed with the hue.  Lightness Value refers to the intensity of light present.


Dithering  Dithering is often used for displaying monochrome images  creating the illusion of new colors and shades by varying the pattern of dots.  Sometime call halftoning.

YCbCr  YCbCr Color Space is used in MPEG video compression standards  • Y is luminance  • Cb is blue chromaticity  • Cr is red chromaticity Y = 0.257*R + 0.504*G 0.098*B 16 Cr = 0.439*R 0.368*G 0.071*B 128 Cb = 0.148*R 0.291*G 0.439*B 128 YIQ color space (Matlab conversion function: rgb2ntsc):

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