-----Original Message----- From: Jasper van de Gronde [mailto:th.v.d.gronde@...528...] Sent: 20 April, 2009 22:00 To: Erik Dahlstrom Cc: Inkscape Devel List Subject: Re: [Inkscape-devel] The bias property for feConvolveMatrix Erik Dahlstrom wrote: > On Wed, 08 Apr 2009 14:09:01 +0200, Jasper van de Gronde > <th.v.d.gronde@...528...> wrote: > >> 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. > > Wouldn't the 'preserveAlpha' attribute[1] be sufficient to control this? No, imagine that the image already has alpha=0.5, then adding a bias of 0.5 suddenly does not correspond to a transparent gray zero response, but rather a transparent white zero response. > ... > There should be some precedent, e.g: > > - Opera 9.x > - Firefox 3.1 > - ASV3 Unfortunately I don't have any of those installed, so if someone could help me test that would be great. I have attached a file that tests numerous cases using bias (and transparency), if someone could try it on his/her favourite renderer that would be great.

-----Original Message----- From: Jasper van de Gronde [mailto:th.v.d.gronde@...528...] Sent: 20 April, 2009 22:54 To: Preben Soeberg Cc: inkscape-devel(a)lists.sourceforge.net Subject: Re: [Inkscape-devel] bugfix for divisor default (was: The bias property for feConvolveMatrix) Preben Soeberg wrote: > I have posted a patch for https://bugs.launchpad.net/inkscape/+bug/193926 > The patch fixes the divisor to be calculated automatically by default. > > Could you take a look at it and commit it? I've had a look and in principle the fix to the sp-feconvolvematrix code seems fine. But: - Could you perhaps base the fix on a more recent version? sp-feconvolvematrix.cpp no longer exists (it is now src/filters/convolvematrix.cpp). - I have hardly any experience with the UI code, so if someone else could take a look at that part that would be great. (Otherwise, if you'll update the patch I'll just try it and commit it if it seems to work.) Thanks for your efforts.

-----Original Message----- From: Jasper van de Gronde [mailto:th.v.d.gronde@...528...] Sent: 21 April, 2009 21:25 To: Preben Soeberg Cc: inkscape-devel(a)lists.sourceforge.net Subject: Re: [Inkscape-devel] bugfix for divisor default Preben Soeberg wrote: > The patches are made on the correct and newest files, and I have tested them > thoroughly. > > I made a mistake, when editing in the patch (removed irrelevant changes in > other files), so I have updated and posted it again. Patch applied, thanks for your input! However, this does expose another issue. Inkscape now uses the default setting when divisor is set to zero, which is not that bad, but other renderers might consider it an error condition (as the spec says) and handle it differently. So, since Inkscape currently outputs divisor="0" when it actually "intents" to use the default values there might be discrepancies between Inkscape and other renderers (and Inkscape would in fact be "wrong"). Any ideas on how to properly resolve this would be appreciated. In my opinion the cleanest solution would be to explicitly allow setting divisor to the default in the UI (making the slider gray for example, while keeping its value in sync with the values in the kernel matrix) and reflecting this in the serialization. Setting the divisor to zero should be prevented in some way. (I have absolutely no idea how to do all this though.)

> ... > There should be some precedent, e.g: > > - Opera 9.x > - Firefox 3.1 > - ASV3 Unfortunately I don't have any of those installed, so if someone could help me test that would be great. I have attached a file that tests numerous cases using bias (and transparency), if someone could try it on his/her favourite renderer that would be great.