Page 195 - DCAP504_Computer Graphics

Computer Graphics

12.4 Summary
• Usage of color in all computer graphics applications helps to clearly depict the images, the
information presented, and also to clearly distinguish the features of images.
• The study of shading models helps to analyze object's surface under different lighting conditions.
• Light has dual nature and color is a mixture of all lights. Light is characterized by brightness, hue,
and saturation.
• Various colors can be obtained by varying the wavelengths of primary colors.
• In computer graphics, color can be handled using indexed color model or RGB color model.
• RGB color model is an additive color model. In RGB color model, a color cube can be used to
specify the colors.
• NTSC YIQ color model is also known as linear transformation of RGB color model and it can be
used to represent colors in color screens.
• According to Phong model, object surfaces might produce a mix of ambient-light reflection and
light-source-dependent diffuse/specular reflection.
• Constant shading of polygon produces uniformly shaded polygon surface.
• Gouraud shading calculates illumination formula for each vertices of a polygon.
• Phong shading involves more calculations.
12.5 Keywords

Additive Color Model: An additive color model uses light directly coming from a source or some sort of
thing that serves as light source. The additive color model usually generates new colors by using red,
green and blue light.
API: An API is a defined set of rules and regulations that a software program needs to follow to access
and utilize the services and resources of other software programs that implements API.
Graphics Processor Unit (GPU): A GPU is a specialized processor that is used to process graphics in a
quick manner than a central processor.
Luminance: Luminance is nothing but the brightness of a color. Luminance is considered as the total
amount of light emitting from a given surface area.

OpenGL: It is an application programming interface that helps to define 2-Dimensional and 3-
Dimensional computer graphics.
Tri-stimulus: It is considered as the total effect of three standard stimuli needed to match a given
sample of light.

12.6 Self Assessment
1. State whether the following statements are true or false:
(a) When the chromaticity of two colors varies, they are represented by two different co-
ordinates.
(b) The CIE chromacy diagram can be used as a universal reference for measuring and
comparing visible colors.
(c) RGB color model is a subtractive color model.

(d) Light has dual nature.
(e) The total energy in the light can be measured using its hue.
(f) Even when the polygon mesh is relatively coarse, Gouraud shading is very useful in
eliminating abrupt modifications.

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