[FFmpeg-devel] [PATCH] lavfi/bwdif: remove interpolated sample clipping

[Thomas Mundt]

Am So., 2. Juli 2023 um 20:58 Uhr schrieb Lynne <dev at lynne.ee>:

> Jul 2, 2023, 20:41 by tmundt75 at gmail.com:
>
> > Am So., 2. Juli 2023 um 18:57 Uhr schrieb Lynne <dev at lynne.ee>:
> >
> >> Jul 2, 2023, 18:54 by dev at lynne.ee:
> >>
> >> > The issue is that clipping the interpolated temporal sample against
> >> > the spatially predicted sample causes artifacts to appear.
> >> >
> >> > Discovered while writing the Vulkan version (where I omitted the
> >> > same check).
> >> >
> >> > The clipping in the code is carried over from yadif. Removing the
> >> > same code in yadif does not make any difference to the output.
> >> > I think that the check was simply ill-adapted to the new prediction
> >> > code and does more harm.
> >> >
> >> > I tested replacing the range clip with only an FFMAX, and only an
> >> > FFMIN, but in both cases, artifacts still appeared.
> >> >
> >> > Test sample 1:
> >> https://files.lynne.ee/testsamples/mbaff_1080i60_idx.mkvTest sample 2:
> >> https://files.lynne.ee/testsamples/mbaff_bdmv_1080i60_8slice.mkv
> >> >
> >> > Command line:
> >> > ./ffmpeg_g -cpuflags 0 -i <INPUT> -vf bwdif=mode=send_field -c:v
> >> rawvideo -y <OUTPUT>.nut
> >> > Make sure to disable the assembly.
> >> >
> >> > Comparisons:
> >> > https://files.lynne.ee/bwdif_01_before.png
> >> > https://files.lynne.ee/bwdif_01_after.png
> >> > Generated from sample 1 via:
> >> > ffmpeg -ss 00:00:00.184 -i <INPUT>.nut -vf
> >> crop=w=420:h=240:x=700:y=300,scale=iw*2:ih*2 -y <OUTPUT>.png
> >> >
> >> > https://files.lynne.ee/bwdif_02_before.png
> >> > https://files.lynne.ee/bwdif_02_after.pngffmpeg -ss 00:00:00.417 -i
> >> <INPUT>.nut -vf crop=w=420:h=240:x=1100:y=200,scale=iw*2:ih*2 -y
> >> <OUTPUT>.png
> >> >
> >>
> >> Corrected links for the second sample:
> >>
> >> https://files.lynne.ee/bwdif_02_before.png
> >> https://files.lynne.ee/bwdif_02_after.png
> >> ffmpeg -ss 00:00:00.417 -i <INPUT>.nut -vf
> >> crop=w=420:h=240:x=1100:y=200,scale=iw*2:ih*2 -y <OUTPUT>.png
> >>
> >> I'm sure I hit a newline. The artifacts are a lot more noticeable in the
> >> second sample.
> >>
> >
> > I developed the bwdif to achieve the best possible balance between speed
> > and quality of all different image contents from the broadcast point of
> > view. This includes moving video as well as moving and static graphic
> > elements. Unfortunately, the improvement of one image content often leads
> > to the degradation of another. The code you removed fundamentally
> > stabilizes the static graphic elements. This outweighs the slightly more
> > frequent artifacts in moving video considering the general purpose of the
> > filter.
> >
>
> Could you post examples? I've been unable to find any that look worse
> with the patch.
>

Unfortunately, I no longer have most of the test material that I used years
ago at the development of the bwdif.
But on the quick I have this clip with an "Archiv" insert. With your patch
the letters are jumping. Without your patch they stay static.
https://www.dropbox.com/s/jzoezjbi3ho9nja/bwdif-test.mov?dl=1
ffmpeg.exe -cpuflags 0 -i "bwdif-test.mov" -vf "bwdif=1:-1:1,
scale=1920:1080" -sws_flags lanczos -aspect 16:9 -c:v libx264 -crf 21
"bwdif_original.mp4"
ffmpeg_lynne_patch.exe -cpuflags 0 -i "bwdif-test.mov" -vf "bwdif=1:-1:1,
scale=1920:1080" -sws_flags lanczos -aspect 16:9 -c:v libx264 -crf 21
"bwdif_lynne_patch.mp4"
https://www.dropbox.com/s/tonsomtkhyaha91/bwdif_original.mp4?dl=1
https://www.dropbox.com/s/aaj8o5yzlocu55z/bwdif_lynne_patch.mp4?dl=1

Regards,
Thomas