Re: [Gimp-developer] Selective gaussian blur port to gegl

[Victor Oliveira <victormatheus gmail com>]

Just a comment, I implemented recently a much faster version of the
bilateral-filter. Though I think there is still some polishing to do,
it is basically working in the CPU and the GPU.

On Sat, Apr 6, 2013 at 4:39 PM, Øyvind Kolås <pippin gimp org> wrote:
> Thank you for poking around looking for more things to bring over to GEGL. I
> do not know much about the GIMP plug-in, but can tell you some other bits of
> information that could be relevant ;)
>
> The core part of "selective gaussian blur" is what is normally called
> "bilateral filtering" in academic image processing circles. GEGL already has
> a (rather slow) bilateral filter implemented contained in
> operations/common/bilateral-filter.c
>
> The specifics of the behavior of GIMPs selective-gaussian blur is something
> I'd consider a historic artifact - that we might not want to preserve in
> future versions.
>
> (As to the lines you've pointed out, looking at them in isolation.. this
> seems to be code that deals with correctly handling alpha; GEGL does this
> normally by processing buffers with premultiplied alpha, this seems to be
> manual hacks that scales the contribution of pixels to the sum by the
> alpha.. and since legacy GIMP is 8bpc,   >>= 8, is the same as /256  and 256
> is 1.0, which normalizes the effect of multiplying by the alpha values
> between 0 and 255.)
>
> /Ø
>
>
> On Sat, Apr 6, 2013 at 12:14 PM, Karthikeyan S <karthikdevel gmail com>
> wrote:
> > Hi all,
> > I am trying to port the selective gaussian blur filter to gegl. I do not
> > understand the following lines in the original gimp code and what purpose
> > they serve.
> >
> > ---
> >
> > Line 668
> > if (has_alpha)
> >  d *= src_b[nb - b]; // ?
> > ---
> >
> > Line 676
> > if (has_alpha)
> > {
> >   rowsum >>= 8; // why?
> >   rowfact >>= 8;
> > }
> >
> > ---
> >
> > Also, as of now, my implementation correctly maintains edges in checker
> > board images while blurring other areas. I am trying to debug another issue
> > wherein I see that the noise pixels (in complete dark background in the
> > checkerboard image)  seem to get smeared out to neighbourhood areas and we
> > get large patches of white arround the blurred pixel (This does not happen
> > in gimp implementation). I am trying to see if the above lines have some
> > clue to that.
> >
> > Thanks,
> > Karthik
> >
> > _______________________________________________
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> > gimp-developer-list gnome org
> > https://mail.gnome.org/mailman/listinfo/gimp-developer-list
>
>
>
> --
> «The future is already here. It's just not very evenly distributed»
>                                                  -- William Gibson
> http://pippin.gimp.org/                            http://ffii.org/
>
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