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Pixel filter
You can choose between several different methods for filtering of pixels. Each pixel filter will look a little bit different. Some produce sharper and some softer images. Some are better when dealing with moire patterns.
Filter radius specifies the amount of “blur”. When radius is large image will look more blurry. With low filter radius images will look sharper.

djwaterman wrote:This is from the wiki;

Pixel filter
You can choose between several different methods for filtering of pixels. Each pixel filter will look a little bit different. Some produce sharper and some softer images. Some are better when dealing with moire patterns.
Filter radius specifies the amount of “blur”. When radius is large image will look more blurry. With low filter radius images will look sharper.

Which? What? How? Which ones are better at moire patterns? What ones produce sharper or softer images? See my point? Sometimes the wiki leaves you with a little bit of knowledge while leaving you clueless.