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

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=111177





--- Comment #9 from Dirk Schulze <krit at webkit.org>  2013-03-03 07:36:17 PST ---
(In reply to comment #7)
> (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] [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.

Did you try to use feConvolveMatrix? This allows you to use a kernel matrix. Maybe if you simulate it, it looks better? It will definitely slower though.

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