Re: [FFmpeg-devel] [PATCH] avfilter/vf_bwdif: Remove undesireable spatial preference logic

[Thomas Mundt <tmundt75@gmail.com>]

Lynne <dev@lynne.ee> schrieb am So., 11. Juni 2023, 20:11:

> Jun 11, 2023, 04:53 by philipl@overt.org:
>
> > On Sat, 25 Mar 2023 00:02:03 +0100
> > Thomas Mundt <tmundt75@gmail.com> wrote:
> >
> >> Hi Philip,
> >>
> >> Philip Langdale <philipl@overt.org> schrieb am Fr., 24. März 2023,
> >> 23:21:
> >>
> >> > bwdif inherited this check from yadif, which was originally
> >> > supposed to prefer the spatial predictor if the temporal predictor
> >> > was too far off.
> >> >
> >> > However, the core bwdif algorithm already accounts for the spatial
> >> > predictor, so this additional check actually ends up preferring a
> >> > worse value, reducing the overall quality.
> >> >
> >> > This was found by cyanreg while writing bwdif_vulkan, and the visual
> >> > improvement is pretty dramatic in some samples. If we agree that
> >> > this change is desirable, we should update all implementations.
> >> >
> >> > Signed-off-by: Philip Langdale <philipl@overt.org>
> >> > ---
> >> >  libavfilter/vf_bwdif.c | 5 -----
> >> >  1 file changed, 5 deletions(-)
> >> >
> >> > diff --git a/libavfilter/vf_bwdif.c b/libavfilter/vf_bwdif.c
> >> > index 65c617ebb3..441bb11e7b 100644
> >> > --- a/libavfilter/vf_bwdif.c
> >> > +++ b/libavfilter/vf_bwdif.c
> >> > @@ -106,11 +106,6 @@ typedef struct ThreadData {
> >> >              interpol = (c + e) >> 1;
> >> >
> >> >  #define FILTER2() \
> >> > -            if (interpol > d + diff) \
> >> > -                interpol = d + diff; \
> >> > -            else if (interpol < d - diff) \
> >> > -                interpol = d - diff; \
> >> > - \
> >> >
> >>
> >> Removing this will make lower thirds and other graphic jump up and
> >> down each frame. It is the main improvement over w3fdif that I have
> >> ported from yadif.
> >> Can you provide samples including still graphics that are improved
> >> with this patch?
> >>
> >
> > Hi Thomas,
> >
> > Sorry for this thread going unanswered for so long. With the Vulkan
> > hwaccel stuff sorted out, I wanted to come back to this. I discussed
> > more with Lynne and we're no longer convinced this change is obviously
> > desirable. You are right about the jumping behaviour - and although
> > there are samples (eg: the burosch ones on samples.ffmpeg.org) which
> > look better with the change, I don't think that's something to over
> > index on.
> >
>
> I don't recall agreeing that this is desirable.
> bwdif_vulkan still looks better than bwdif or bwdif_cuda (and it's got
> proper edge handling).
>

Could you please prove this claim with some samples? I don't have any
suitable hardware for Vulkan.
Just saw that bwdif_vulkan was added to master. Somehow I didn't see the
commit in the cvs log.

>
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