[FFmpeg-devel] Re: [PATCH] vf_colorspace: Add an option to clamp trc LUT output

[Drew Dunne via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

Sure, I can submit it there. Is there documentation on how to submit a
patch there? Do I just submit it as a pull request?

On Tue, Aug 26, 2025 at 2:33 PM Ronald S. Bultje <rsbultje@gmail.com> wrote:

> Hi Drew,
>
> Thanks for the bug report!
>
> On Mon, Aug 25, 2025 at 10:50 AM Drew Dunne via ffmpeg-devel <
> ffmpeg-devel@ffmpeg.org> wrote:
>
>> A solid color image of 8-bit YUV: Y=157, U=164, V=98.
>>
>> Specify the input as:
>>
>> Input range: MPEG
>> In color matrix: BT470BG
>> In color primaries: BT470M
>> In color transfer characteristics: Gamma 28
>>
>> Output as:
>> Out color range: JPEG
>> Out color matrix: BT.709
>> Out color primaries: BT.709
>> Out color transfer characteristics: BT.709
>>
>> During the calculation you get:
>>
>> Input YUV:                             y=157,      u=164,      v-98
>> Post-yuv2rgb BT.470BG:                 r=0.456055, g=0.684152, b=0.928606
>> Post-apply gamma28 linear LUT:         r=0.110979, g=0.345494, b=0.812709
>> Post-color rotation BT.470M to BT.709: r=-0.04161, g=0.384626, b=0.852400
>> Post-apply Rec.709 delinear LUT:       r=-0.16382, g=0.615932, b=0.923793
>> Post-rgb2yuv Rec.709 matrix:           y=120,      u=190,      v=25
>>
>> Where with this change, the delinear LUT output would be clamped to 0,
>> so the result would be:
>> r=0.000000, g=0.612390, b=0.918807 and a final output of
>> y=129, u=185, v=46
>
>
> So for those of us playing along, a repro looks like this:
>
> $ hexdump /tmp/in.yuv
> 0000000 9d9d 9d9d 62a4
> $ git diff
> diff --git a/libavfilter/vf_colorspace.c b/libavfilter/vf_colorspace.c
> index e1f4725f635..512eb620fcf 100644
> --- a/libavfilter/vf_colorspace.c
> +++ b/libavfilter/vf_colorspace.c
> @@ -348,11 +348,20 @@ static int convert(AVFilterContext *ctx, void *data,
> int job_nr, int n_jobs)
>           */
>          s->yuv2rgb(rgb, s->rgb_stride, in_data, td->in_linesize, w, h,
>                     s->yuv2rgb_coeffs, s->yuv_offset[0]);
> +        printf("post-yuv2rgb - R: %d, G: %d, B: %d\n",
> +               rgb[0][0], rgb[1][0], rgb[2][0]);
>          if (!s->rgb2rgb_passthrough) {
>              apply_lut(rgb, s->rgb_stride, w, h, s->lin_lut);
> -            if (!s->lrgb2lrgb_passthrough)
> +            printf("post-linearize - R: %d, G: %d, B: %d\n",
> +                   rgb[0][0], rgb[1][0], rgb[2][0]);
> +            if (!s->lrgb2lrgb_passthrough) {
>                  s->dsp.multiply3x3(rgb, s->rgb_stride, w, h,
> s->lrgb2lrgb_coeffs);
> +                printf("post-rgb2rgb - R: %d, G: %d, B: %d\n",
> +                       rgb[0][0], rgb[1][0], rgb[2][0]);
> +            }
>              apply_lut(rgb, s->rgb_stride, w, h, s->delin_lut);
> +            printf("post-delinearize - R: %d, G: %d, B: %d\n",
> +                   rgb[0][0], rgb[1][0], rgb[2][0]);
>          }
>          if (s->dither == DITHER_FSB) {
>              s->rgb2yuv_fsb(out_data, td->out_linesize, rgb,
> s->rgb_stride, w, h,
> $ make -j4 && ./ffmpeg -s 2x2 -pix_fmt yuv420p -f rawvideo -c:v rawvideo
> -i /tmp/in.yuv -vf
> colorspace=ispace=bt470bg:iprimaries=bt470m:itrc=gamma28:irange=mpeg:range=jpeg:all=bt709
> -y /tmp/out.yuv
> [..]
> post-yuv2rgb - R: 13076, G: 19616, B: 26625
> post-linearize - R: 3182, G: 9906, B: 23302
> post-rgb2rgb - R: -1193, G: 11028, B: 24440
> post-delinearize - R: -4697, G: 17660, B: 26487
>
> Patch looks OK. Drew, would it be possible to submit the patch at
> code.ffmpeg.org so I can merge it using our new system?
>
> Thanks,
> Ronald
>


-- 
Drew Dunne
asdunne@google.com
_______________________________________________
ffmpeg-devel mailing list -- ffmpeg-devel@ffmpeg.org
To unsubscribe send an email to ffmpeg-devel-leave@ffmpeg.org