Page 66 - DCAP504_Computer Graphics

Unit 5: Scan Conversion II

Figure 5.5 (a) shows a rapidly varying square wave is sampled uniformly at the instants shown by dots.
Based on these samples, a lower frequency signal appears to be a square wave as shown as Figure 5.5
(b).

Figure 5.5 (a): Aliasing Signals in Square Wave

Source: Computer Graphics, The McGraw-Hill Companies, Amarendra N Sinha, Arun D Udai, Chapter 3

Figure 5.5 (b) : Aliasing in Sampling of Signals

Source: Computer Graphics, The McGraw-Hill Companies, Amarendra N Sinha, Arun D Udai, Chapter 3
The process of separation of the pixels in raster display also results in aliasing. The jagged appearance
of a black rectangle is caused by the pixel display in a fixed rectangle as shown in Figure 5.6.

Figure 5.6 : Aliasing of a Rectangle

Source: Computer Graphics, The McGraw-Hill Companies, Amarendra N Sinha, Arun D Udai, Chapter 3
Aliasing occurs for many objects where its attributes are calculated only if the size of a pixel is bigger
than the object. However, it will not affect the picture. Alternatively, if the small object covers the point
at which the pixel attributes are calculated, then it may influence those attributes. Figures 5.7 (a) and (b)
shows the effect.

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