1. Morphological Antialiasing
Author:Alexander Reshetov
Intel Labs
Speaker: 李仲元

2. Outline
 Introduction
 Previous method
◦ Super Sampling Anti-Aliasing (SSAA)
◦ Multi Sampling Anti-Aliasing (MSAA)
 Morphological Anti-Aliasing (MLAA)
◦ Black-and-white image
◦ Color image
 Experiment
 Reference
◦ Sub-pixel Reconstruction Anti-Aliasing (SRAA)

3. Introduction
 Anti-aliasing
Call of Duty: World at War

4. Previous method
 Full scene Anti-aliasing avoid aliasing on
full-screen images
 Super-Sampling Anti-aliasing
 MultiSampling Anti-Aliasing
 CoverageSampling Anti-Aliasing
 Custom Filter Anti-Aliasing

5. Previous method - SSAA
 Upscale image to higher resolution
 Then downsampling it to the desired size
 Brute-Force method

6. Previous method - MSAA
 Like SSAA, but just do super-sampling for
Z-buffer and Stencil Buffer
 Assume that the change of color in one
pixel is not obvious
 Disadvantages :
◦ If the alpha value of a translucent fragment is
not within a specified range, it will be
discarded after alpha testing

7. Previous method - MSAA

8. Previous method
 Different Sampling method will affect the
result
 High quality result with high cost
 Must combine with forward rendering

9. Morphological Anti-Aliasing
 Algorithm
for black-and-white implementation
◦ Step 1: Separate different color area
◦ Step 2: Classify separation line
◦ Step 3: Compute new color for cells

10. Step 1: Separate
Assume that border pixels are extended
into additional imaginary rows and columns

11. Step 2: Classify
 Look for other separation lines which are
orthogonal to the current one at its farthest
vertices
 A single separation line can be a part of
multiple patterns (up to four)
 classify separation lines into the following
three categories:
◦ 1. Z-shaped pattern
◦ 2. U-shaped pattern
◦ 3. L-shaped pattern

12. Step 2: Classify

13. Step 3: Compute
 I) Anti-aliasing area
 Z and U shapes can be split into two L-
shapes
 Substep 1. consider each L-shape to be
formed by a primary edge found at the
first step, secondary edge found at the
second step

14. Step 3: Compute

15. Step 3: Compute
 Substep 2. Connect the middle point of
the secondary edge with the remaining
vertex of the primary edge

16. Step 3: Compute

17. Step 3: Compute
 II) Computing blending weights
 We calculate the area of each trapezoid
attached to the primary edge and use it
to compute new color of these cells as
follows:

18. Step 3: Compute
ｃ５ = １／３*０ ＋ ２／３*１
ｄ５＝１／２４*０ ＋ ２３／２４*１

19. Step 3: Compute

20. Morphological Anti-Aliasing
 Algorithm
for color image
◦ Step 1: Found discontinuities in color image
◦ Step 2: Classify separation line
◦ Step 3: Pattern search
 Optimization
 Limitation
 Feature

21. Step 3: Pattern search

22. Step 3: Pattern search
 Can use different method to get answers
◦ Solve the equation for each channel, then average
the solution
◦ Summing all values to form a single numerical
value(assign different weights to different
channels, deferring more advanced luminance
processing until GPU implementation)
 If the found values of hc and hd are in the [0,
1] interval, we process the tested shape,
otherwise ignore it

23. Morphological Anti-Aliasing
 Feature
◦ MLAA can be used for any image processing
task and does not use any data besides color
values
◦ Can combine with deferred rendering,
allowing for better processor utilization
◦ The algorithm achieves reasonable
performance without any noticeable impact
◦ The “best in class” approach for anti-aliased
deferred shading before Feb, 2011

24. Morphological Anti-Aliasing
 Optimization
◦ searching for color discontinuities
 Each RGBA color requires 32 bits, so 4 RGBA
pixels will fit into one SSE register
 Limitation
◦ Running time depends on number of edges
 For the CPU version of MLAA, processing about
20M pixels per second on a single 3GHz core
◦ Can’t respect geometric boundaries well

25. Experiment
Top row: bitmap font;
Second row: TrueType font (antialiased)
Third row: MLAA processing of bitmap font
Ffourth row: MLAA processingof TrueType font.
Font size from left to right: 24, 12, 8, and 6

26. Experiment

27. Reference - SRAA
 Subpixel Reconstruction Antialiasing
for Deferred Shading
◦ Matthäus G. Chajdas, Morgan McGuire, David
Luebke
◦ ACM SIGGRAPH Symposium on Interactive 3D
Graphics and Games 2011

28. Reference - SRAA
 An efficient algorithm for antialiasing
images as a post-process
 Increase performance for small quality
reductions
 Detailed analysis of the algorithm and
comparison to MLAA
 Evaluation on real game scenes including
texture, specular reflection, geometric
aliasing, emission, and bloom

29. Reference - SRAA