Page 180 - DCAP504_Computer Graphics

Unit 12: Color and Shading Model

Brightness is similar to physical property of light called luminance. The total energy in the light can be
measured using its luminance. The second character, hue can be used to differentiate a white light from
a red or green light. The third character is the saturation which describes the degree of brightness.
When two red lights differ in luminance and degree of brightness they might
become pure/saturated red or pale/unsaturated red.

In reality, light scatters to infinite distance. Objects can be seen only when light falls on the object. In
computer graphics we do not want the light to be scattered because the distance of light and its effect on
objects, and so on needs to be calculated optimally to create proper shading of an object. If you have
more light on a particular object then the Graphics Processor Unit (GPU) will take more time for
calculation.
In 3-D computer simulations, use a model that has a final range of effect. Modern graphic engines or
some custom projects should contain effective optimization methods for the calculation of light on an
object. If we use all the lights with an infinite range and all the geometry together we may find it
difficult to calculate the effect of each light. It may be difficult, even if the effect of light is undetectable
.i.e. too small effect to an object.
Lights, scene, and shades provide a proper way to create rich and fast 3-D graphics. It is a form of art to
create colorful, precise, rich, and fast 3-D graphics.
In 2-D, light is used to simulate depth and shade, and to simulate movement.
Consider a ship that is moving towards a star. When you create a 2-D image for
this, it will be very attractive if the ship appears as if it has been lit by the star.
The simple way to do this is to represent the pixels on the side of the ship which
is facing the star brighter, and the pixels on the other side should be made
darker.

The impact of light in 2-D is not automated but 2-D graphics designer needs to add the impact of light
on the objects.
Color

The most exciting aspect of both human perception and computer graphics is color. A visible color can
be characterized by a function C(λ) that takes wavelengths of about 400 to 700 nano meter (nm) as
shown in figure 12.2.

Figure 12.2: Typical Color Distribution

Source: Xiang. Z., Plstock. R. (2006). Computer Graphics. 2nd Edition. Tata McGraw Hill. Pg no. 290.
In the visible spectrum, the value λ represents the intensity of the wavelength of color light. Human
visual system has three types of cones responsible for color vision. Human brains are not capable of

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