This presentation introduces anti-aliasing techniques. It begins with defining anti-aliasing as a technique to reduce jagged edges by softening lines and edges. It then shows before and after examples of anti-aliased versus non-anti-aliased polygons. Finally, it discusses the two main anti-aliasing approaches of area sampling and super-sampling and provides details on how each technique works.

1. WelcomeTo Our Presentation
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2. Introducing Group Members
Name ID
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3. Anti-Aliasing

4. What does Antialiasing mean?
“ Antialiasing is a software technique for diminishing jaggies- stair step -like
lines that should be smooth. ”
Even though the jagged appearance
is reduced, it makes the image look
fuzzier.
(Anti-Aliasing (with and without))

5. Anti-aliasing: Definition
Antialiasing is a technique used in digital imaging to reduce the visual defects
that occur when high-resolution images are presented in a lower resolution
output devices like the monitor or printer.

6. Before and After of Anti-Aliasing
Aliased polygons
(jagged edges)
Anti-aliased polygons

7. Antialiasing Techniques
• Two general approaches: Area sampling and super-sampling
• Area sampling approaches sample primitives with a box (or Gaussian, or whatever)
rather than spikes
1. Requires primitives that have area (lines with width)
2. Sometimes referred to as pre-filtering
• Super-sampling samples at higher resolution, then filters down the resulting image
i. Sometimes called post-filtering
ii. The prevalent form of anti-aliasing in hardware

8. Area Sampling
• shade pixels according to the area covered by thickened line
• this is un-weighted area sampling
• a rough approximation formulated by dividing each pixel into a finer grid of
pixels

9. Super-sampling
• Sample at a higher resolution than required for display,
and filter image down
• Issues of which samples to take, and how to average them
• 4 to 16 samples per pixel is typical
• Samples might be on a uniform grid, or randomly
positioned, or other variants
• Number of samples can be adapted

10. Anti aliasing in OpenGL
• OpenGL calculates a coverage value for each fragment based on
the fraction of the pixel square on the screen that it would cover.
• In RGBA mode, OpenGL multiplies the fragment’s alpha value by its
coverage.
• Resulting alpha value is used to blend the fragment with the
corresponding pixel already in the frame buffer.