[FFmpeg-devel] [PATCH v2] avfilter/vf_edgedetect: properly implement double_threshold()

[Alexander Strasser]

On 2020-07-04 23:19 -0400, Andriy Gelman wrote:
> On Sun, 05. Jul 09:37, lance.lmwang at gmail.com wrote:
> > On Sat, Jul 04, 2020 at 01:03:48PM -0400, Andriy Gelman wrote:
> > > On Mon, 29. Jun 09:26, Valery Kot wrote:
> > > > On Sun, Jun 28, 2020 at 12:03 AM Andriy Gelman <andriy.gelman at gmail.com> wrote:
> > > > >
> > > > > lgtm. I saw a small improvement when testing.
> > > > >
> > > > > Would be nice to allow weak edges that become strong to trigger neighboring weak
> > > > > edges in the future.
> > > >
> > > > Thanks for the comment.
> > > >
> > > > You are right, ideally double_threshold should be recursive (seed from
> > > > each "high" peak and spread over "low" peaks). But then potentially we
> > > > may end up with width*height/2 recursion depth, which may lead to
> > > > stack overflow. So probably some recursion limit is needed, and hence
> > > > suboptimal solution.
> > > >
> > > > Or iterative approach, running through the complete image again and
> > > > again checking if "low" peaks are touching already selected edge
> > > > pixels. Stop when no new pixels can be added to the edge. Better, but
> > > > still potentially width*height/2 iterations with width*height
> > > > operations each, completely killing performance.
> > > >
> > > > Maybe later I'll try to implement it in a generic way, but this is out
> > > > of scope for this patch.
> > > >
> > > > Regards,
> > > >
> > > > Valery Kot
> > >
> > > Any objections if I apply this patch?
>
> >
> > The patch look fine to me, but no sign-off?
> >
>
> Thanks, will add one.

I guess it's OK to push. In my few tests for some cases it looked
a bit better.

I didn't understand why this doesn't make things worse for the
outermost frame of pixels, but Valery commented it wouldn't make
any difference because of the surrounding code.

I just looked at that function and because it checks all the eight
surrounding pixels, I thought we might now miss cases that wouldn't
have been missed before. Should of course be usually be better for
most pictures.

Anyway I couldn't get around to build a mental model for this call,
so I might well be missing context.


  Alexander