New Anti-Aliasing menus explained

This post explains new Anti-Aliasing options introduced in the June 1st, 2010 update.

Filter > Anti-Aliasing > Clip HDR Before Averaging

This menu item lets you clip the sample colors into the LDR range before they are averaged to produce an anti-aliased pixel. This is needed to fix a common problem that arises from HDR usage -- when sample colors are too bright, simply averaging them produces suboptimal anti-aliasing.

Consider a situation when there are five samples, all within the same pixel, that need to be averaged to produce the anti-aliased pixel color. The brightness of first four samples is within the normal 0...1 LDR range, but the fifth sample has its brightness somewhere in the millions. The averaged brightness will be on the order of several hundred thousand -- which exceeds the LDR range of the final pixel, which will cause excessive brightness of anti-aliased edges.

Turning HDR clipping on using the menu item referenced above lets you clip the RGB channels of the samples before they are averaged, which leads to smoother anti-aliased edges.

Here's the picture that shows both cases:

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