[FFmpeg-devel] [PATCH] swscale: Check whether slice height is multiple of chroma subsample.

[Michael Niedermayer]

On Fri, Mar 12, 2010 at 07:38:02PM -0300, Ramiro Polla wrote:
> On Tue, Feb 23, 2010 at 11:10 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Tue, Feb 23, 2010 at 10:48:05PM -0300, Ramiro Polla wrote:
> >> On Tue, Feb 23, 2010 at 9:07 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
> >> > On Tue, Feb 23, 2010 at 12:20:37AM -0300, Ramiro Polla wrote:
> >> >> Hi,
> >> >>
> >> >> Check whether slice height is multiple of chroma subsample.
> >> >>
> >> >> Currently if we take a 410p image and rescale with sliceH = 1, the
> >> >> output is black&white. I did this using the test tool at [1] (renamed
> >> >> to swscale-test2) and the command:
> >> >> ./swscale-test2 -i input.bmp -sws_flags bicubic -pix_fmt yuv410p -s
> >> >> 320x320 -scale -sliceH 1 -pix_fmt bgr24 -scale -o output.bmp
> >> >>
> >> >> I found it weird that this code in utils.c expects the slices to start
> >> >> on subsample boundaries (by shifting nextSlice back and forth), but
> >> >> sws_scale() doesn't:
> >> >> ? ? // calculate buffer sizes so that they won't run out while
> >> >> handling these damn slices
> >> >> ? ? c->vLumBufSize= c->vLumFilterSize;
> >> >> ? ? c->vChrBufSize= c->vChrFilterSize;
> >> >> ? ? for (i=0; i<dstH; i++) {
> >> >> ? ? ? ? int chrI= i*c->chrDstH / dstH;
> >> >> ? ? ? ? int nextSlice= FFMAX(c->vLumFilterPos[i ? ] + c->vLumFilterSize - 1,
> >> >> ? ? ? ? ? ? ? ? ? ? ? ? ? ?((c->vChrFilterPos[chrI] +
> >> >> c->vChrFilterSize - 1)<<c->chrSrcVSubSample));
> >> >>
> >> >> ? ? ? ? nextSlice>>= c->chrSrcVSubSample;
> >> >> ? ? ? ? nextSlice<<= c->chrSrcVSubSample;
> >> >> ? ? ? ? if (c->vLumFilterPos[i ? ] + c->vLumBufSize < nextSlice)
> >> >> ? ? ? ? ? ? c->vLumBufSize= nextSlice - c->vLumFilterPos[i];
> >> >> ? ? ? ? if (c->vChrFilterPos[chrI] + c->vChrBufSize <
> >> >> (nextSlice>>c->chrSrcVSubSample))
> >> >> ? ? ? ? ? ? c->vChrBufSize= (nextSlice>>c->chrSrcVSubSample) -
> >> >> c->vChrFilterPos[chrI];
> >> >> ? ? }
> >> >>
> >> >> Ramiro Polla
> >> >> [1] http://article.gmane.org/gmane.comp.video.ffmpeg.devel/102702
> >> >
> >> >> ?swscale.c | ? ?5 +++++
> >> >> ?1 file changed, 5 insertions(+)
> >> >> cd845850f322996173e636f2655b7b4d5880feb4 ?0004-Check-whether-slice-height-is-multiple-of-chroma-sub.patch
> >> >> From 7b2354c9cf66eaf8d51b527239bc1403354b999c Mon Sep 17 00:00:00 2001
> >> >> From: Ramiro Polla <ramiro.polla at gmail.com>
> >> >> Date: Tue, 23 Feb 2010 00:12:51 -0300
> >> >> Subject: [PATCH] Check whether slice height is multiple of chroma subsample.
> >> >
> >> > problem is that swscale can return such chroma != luma slices and
> >> > chaining slices scalers should work
> >>
> >> Sorry, I don't understand what you mean by swscale returning chroma !=
> >> luma slices. Does this mean swscale should support any combination of
> >> chaining slices, even if it's sliceH = 1?
> >
> > stefano talked about luma != chroma slices
> > i assumed these where generated by the scaler
> > if so the scaler must either support them as input or never
> > generate them as output
> 
> Hmm, nevermind. My test program was buggy. But I still didn't
> understand what the luma != chroma slices issue was about.

heres different and simpler example

you have a video of 320x239 pixels
it cannot be represented by slices that have 2*chroma lines = luma lines

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

It is not what we do, but why we do it that matters.
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