Page 186 - DCAP504_Computer Graphics

Unit 12: Color and Shading Model

The figure 12.5 depicts a color cube.

Figure 12.5: Color Cube

Now let us discuss how a color cube can be used to specify any color. Consider the example of Open
Graphics Library (OpenGL). OpenGL is an Application Programming Interface (API) that helps in
defining 2-D and 3-D computer graphics.

OpenGL uses the color cube as shown below:
To draw-in red, OpenGL issues the following function call:
glCo1or3f (l.0, 0.0, 0.0);
The execution of glColor3f (1.0, 0.0, 0.0) function will set the current image color to red. The reason is
that the color is part of the state where red color remains the same until color is changed. The 3f is used
to tell a program that we are using a tri-color (RGB) model.

Make a list of colors that can be generated by mixing blue and green, and blue and red.

Hue, Saturation, and Intensity (HIS) Model
Similar to light, even the color can be differentiated by three quantities such as hue, saturation, and
intensity. The Hue, Saturation, and Intensity (HSI) color model is an effective tool for developing image
processing algorithms depending on color descriptions that are natural and intuitive to the users who
use those algorithms.

Conversion from RGB to HIS can be done using the following equations:
H=arctan (L/M)
2 1/2
S= (L +M )
2
I=N√3

LOVELY PROFESSIONAL UNIVERSITY 179