De : Jasper van de Gronde <th.v.d.gronde@...528...>
À : Inkscape Devel List <inkscape-devel@...842...rceforge.net>
Envoyé le : Mercredi, 8 Avril 2009, 14h09mn 01s
Objet : [Inkscape-devel] The bias property for feConvolveMatrix
The SVG standard defines a "bias" property for feConvolveMatrix
to
offset the result of the filter. It specifies that this value should
simply be added to the result for each channel. Implicitly the standard
defines that these are premultiplied color values, however, this seems
to make little sense, as the bias has very little meaning without taking
the alpha channel into account.
The standard also says that one of the applications of a bias is "to
have 0.5 gray value be the zero response of the filter", this seems to
be directly contradictory with adding bias to the premultiplied values
(as then the same bias could suddenly stand for white if alpha was 0.5).
So, what to do? Batik doesn't seem to support bias!=0 at all, so there
is also no precedent. I currently let feConvolveMatrix make bias
relative to alpha.
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