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20160127 - Temporal AA Neighborhood Clamp
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+
Thoughts too long for the twitter thread on this,
+back from my memory of working on this problem...
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+In TAA the purpose of the neighborhood clamp is to remove ghosting.
+Using the surrounding local neighborhood of the current frame
+to bound the color of the reprojection of the prior frame.
+Many techniques have been tried here,
+including using the min and max of the neighborhood as an AABB to clip to.
+Clipping to two AABBs one in RGB and the other in YCoCg, for a tigher bound.
+Etc.
+It is possible to continue down this path adding more complex and tigher bounds shapes,
+and doing better clipping for when colors are out of bounds.
+But ultimately it seemed like this exploration had passed the optimum !/$ point,
+and settled on the following low-tech solution for the fast path,
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+
+- Work in YCoCg.
+- Can reduce to 5 sample neighboorhood in a + pattern.
+- Use simple min and max instead of clipping to AABB.
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Why?
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+Lets reduce the problem to strictly monochrome.
+The complex 3D bound shape is now reduced to a 1D segment
+defined by the min and max of the neighborhood.
+When the neighborhood is high frequency and high contrast,
+which is common say with a field of grass,
+the min can be a shadow tone, and the max can be a bright highlight.
+Then just about any reprojection passes the neighborhood clamp without adjustment,
+and ghosting results.
+Or even if the reprojection gets clampped, it will be at the extreme ends of the large segment,
+resulting in distortion to the image.
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+
+Ultimately this kind of approach cannot solve the problem at hand,
+so I stopped searching in this specific solution space...
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