clarification of clamping of filter results

In Section 15.7.1, the spec says that "The RGBA result from each
filter primitive will be clamped into the allowable ranges for
colors and opacity values. Thus, for example, the result from a given filter primitive will have any negative color values or opacity values
adjusted up to color/opacity of zero." It needs to be clarified what
happens if an operation on premultiplied values yields color values
greater than the alpha value. The Adobe Viewer seems to clamp the
color values down (as far as I can tell) whereas Batik clamps the
alpha values up (at least in the arithmetic FeComposite filter
primitive). I feel that the former tends to produce the results one
would expect, but in any case the differences can be dramatic and
this needs to be standardized.

Received on Wednesday, 11 February 2004 09:30:13 UTC