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# Color Models Concepts

### Color

A typical observer can discern between a dozen to three dozen distinct grey levels or intensity variations. If we add color, then a typical observer can discern thousands of color shades and intensities. Also, color plays a very important role in image analysis when used as a descriptor. A full color image, also known as a True Color image, has three different bands (R=red, G=green, B=blue), one per color.

### Color Models

A color model is a 3D unique representation of a color. There are different color models and the use of one over the other is problem oriented. For instance, the color model RGB is used in hardware applications like PC monitors, cameras and scanners, the CMY color model is used in color printers, and the YIQ model in television broadcast. In color image manipulation the two models widely used are HSI and HSV.

Below is an RGB image and its data structure. Each pixel has three components: Red, Green and Blue components, which added together can generate most of the existent colors.

A RGB color image and its representation in Khoros 2 polymorphic data model

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)

RGB Color Cube Color Model

The CMY and YIQ color models are obtained from the RGB color model by performing the following conversions:

a)RGB to CMY Conversion; b)RGB to YIQ Conversion
a) | b)