[Webkit-unassigned] [Bug 111177] feGaussianBlur shows banding under certain circumstances

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Sat Mar 2 12:37:49 PST 2013


--- Comment #7 from lars.sonchocky-helldorf at hamburg.de  2013-03-02 12:40:13 PST ---
(In reply to comment #6)
> (In reply to comment #4)
> > Created an attachment (id=191036)
 --> (https://bugs.webkit.org/attachment.cgi?id=191036&action=review) [details] [details]
> > Screenshot using Pixie
> > 
> > This screenshot shows the banding (alternation of darker and brighter bands) using Pixie. If SVG is supposed to replace flash such details count.
> So the way I interpret this, the complaint in not strictly related to the presence of bands (they're unavoidable withing a discrete colorspace), but to their non-monotonic nature (lighter-darker-lighter instead of lighter-darker-darkerstill).
> AFAICT the color component difference between adjacent bands is not larger than one (as expected), but the alternation is indeed non-monotonic: #565656 -> #575757 -> #565656 -> #555555 -> #545454 -> #555555.
> > I expect a smooth gradient without such alternations.
> That may be the root of the problem though: this is a Gaussian blur, not a gradient. I'm no feGaussianBlur expert, but your expectation may be unfounded.

If you have a look at a Gaussian distribution curve it is indeed smooth and not jagged. So my expectation is not unfounded.

> I haven't tested IE and FF can't handle the samples, but Opera definitely implements feGaussianBlur similarly.

Might be, but then Opera is also wrong. There might be a problem with the algorithm as such (I must confess I did not look at the algorithm used).

It boils down to the point that what is currently there is just not usable. It looks awkward. And please don't tell me to use a gradient instead. This is just a test case I provide here to show what is going on. I need to use feGaussianBlur (I use an animated version of this where I animate the parameter stdDeviation) and I know what I am doing.

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