blur calculation incorrect

[elatllat]

As noted here:
https://www.youtube.com/watch?v=LKnqECcg6Gw
there should be no dark lines between 2 blurred differently colored(red and green) objects.

[Alvin Penner (apenner)]

could you attach an svg file?

[su_v (suv-lp)]

Please read
http://article.gmane.org/gmane.comp.graphics.inkscape.devel/45745

[Jaspervdg (jaspervdg)]

Indeed, although one can definitely argue the result is "wrong", but given that Inkscape (by default) computes this filter in the sRGB colour space it is in fact correct. As has been pointed out on the mailing list the latest version of Inkscape can actually also work in the linearRGB colour space, but per the SVG standard this has to be explicitly requested.

On the other hand, the default in the SVG spec is to use linearRGB for filters, while Inkscape (for backwards compatibility) essentially defaults to sRGB. If anyone wants to get into the discussion of whether or not Inkscape should default to linearRGB (and how to orchestrate the transition), I suggest using the mailing list for that. And keep in mind that while the SVG spec defaults to linearRGB for filters, it defaults to sRGB for everything else: http://www.w3.org/TR/SVG/painting.html#ColorInterpolationProperties (which could lead to strangely inconsistent results between filters and gradients or normal compositing operations for example; it would also require quite a few colour space conversions to go back and forth between sRGB and linearRGB), and that by no means all viewers correctly implement linearRGB support.

[Tavmjong Bah (tavmjong-free)]

It shouldn't be a big problem to set the default in Inkscape to use linearRGB for new filters. Old content created by Inkscape that doesn't have 'color-interpolation-filters' set won't render correctly in browsers so I don't think it is a big deal to use 'linearRGB' for this. Inkscape's canned filters have had 'color-interpolation-filters' set for some time (at least since 0.48).

The bigger problems is for non-filter blending. I don't even think that 'color-interopolation' is in the new CSS blending specification. While it's been in SVG forever, I don't know of single browser that implements it. And I am not sure how it can be implemented using Cairo. Implementation in filters was relatively easy as everything is converted to a bitmap and one just has to convert the bitmaps on the fly to and from linear RGB and save the result as sRGB at the end.