[FFmpeg-devel] [PATCH 1/3] lavfi/vf_psnr: add warning when color ranges differ

[Chema Gonzalez]

Removed "Warning: " tidbit in the 3 patches.

-Chema

On Sat, Apr 1, 2023 at 1:14 AM Paul B Mahol <onemda at gmail.com> wrote:
>
>
>
> On Fri, Mar 31, 2023 at 6:49 PM Chema Gonzalez <chemag at gmail.com> wrote:
>>
>> The PSNR filter uses the pixel values without considering
>> the color ranges. This is incorrect. Patch adds a warning
>> so at least the user knows it.
>>
>> Let's see an example:
>>
>> (1) Let's get a simple black pixel/white pixel image.
>> ```
>> $ echo -n -e "\x00\x00\x00\xff\xff\xff" > /tmp/foo.rgb24
>> ```
>>
>> (2) From this image, let's distill full and limited range y4m
>> copies.
>>
>> ```
>> $ ffmpeg -y -f rawvideo -video_size 2x1 -pix_fmt rgb24 -i /tmp/foo.rgb24 -vf scale="out_range=full" -pix_fmt yuv420p /tmp/foo.full.y4m
>> $ xxd /tmp/foo.full.y4m
>> 00000000: 5955 5634 4d50 4547 3220 5732 2048 3120  YUV4MPEG2 W2 H1
>> 00000010: 4632 353a 3120 4970 2041 303a 3020 4334  F25:1 Ip A0:0 C4
>> 00000020: 3230 6a70 6567 2058 5953 4353 533d 3432  20jpeg XYSCSS=42
>> 00000030: 304a 5045 4720 5843 4f4c 4f52 5241 4e47  0JPEG XCOLORRANG
>> 00000040: 453d 4655 4c4c 0a46 5241 4d45 0a00 ff80  E=FULL.FRAME....
>> 00000050: 80                                       .
>> ```
>>
>> and
>>
>> ```
>> $ ffmpeg -y -f rawvideo -video_size 2x1 -pix_fmt rgb24 -i /tmp/foo.rgb24 -vf scale="out_range=limited" -pix_fmt yuv420p /tmp/foo.limited.y4m
>> $ xxd /tmp/foo.limited.y4m
>> 00000000: 5955 5634 4d50 4547 3220 5732 2048 3120  YUV4MPEG2 W2 H1
>> 00000010: 4632 353a 3120 4970 2041 303a 3020 4334  F25:1 Ip A0:0 C4
>> 00000020: 3230 6a70 6567 2058 5953 4353 533d 3432  20jpeg XYSCSS=42
>> 00000030: 304a 5045 4720 5843 4f4c 4f52 5241 4e47  0JPEG XCOLORRANG
>> 00000040: 453d 4c49 4d49 5445 440a 4652 414d 450a  E=LIMITED.FRAME.
>> 00000050: 10eb 8080                                ....
>> ```
>>
>> Note that the 2x images are the same (both have 1x pixel at the
>> darkest black, and one at the brightest white). Only difference
>> is the range.
>>
>> (3) Let's calculate the PSNR score:
>> ```
>> $ ./ffmpeg -filter_threads 1 -filter_complex_threads 1 -i /tmp/foo.full.y4m -i /tmp/foo.limited.y4m -lavfi "psnr" -f null -
>> ...
>> [Parsed_psnr_0 @ 0x2f5dac0] PSNR y:22.972065 u:inf v:inf average:25.982365 min:25.982365 max:25.982365
>> ```
>>
>> As we are comparing an image with itself, we expect "y:inf" as the
>> luma PSNR. Issue here is that the PSNR filter just uses the pixel
>> values, ignoring the color ranges.
>>
>> A possible solution would be to have the filter do the conversion.
>>
>> Proposed solution is to add a warning.
>>
>> ```
>> $ ./ffmpeg -filter_threads 1 -filter_complex_threads 1 -i /tmp/foo.full.y4m -i /tmp/foo.limited.y4m -lavfi "psnr" -f null -
>> ...
>> [Parsed_psnr_0 @ 0x2f5dac0] Warning: master and reference frames use different color ranges (pc != tv)
>
>
>
> NAK
>
> "Warning: " part is not needed.
>
>> ...
>> [Parsed_psnr_0 @ 0x2f5dac0] PSNR y:22.972065 u:inf v:inf average:25.982365 min:25.982365 max:25.982365
>> ```
>>
>> Tested:
>>
>> Ran fate.
>> ```
>> $ make fate -j
>> ...
>> TEST    seek-lavf-ppmpipe
>> TEST    seek-lavf-pgmpipe
>> TEST    seek-lavf-mxf_opatom
>> ```
>> ---
>>  libavfilter/vf_psnr.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/libavfilter/vf_psnr.c b/libavfilter/vf_psnr.c
>> index 15cde7e8c8..bd33322593 100644
>> --- a/libavfilter/vf_psnr.c
>> +++ b/libavfilter/vf_psnr.c
>> @@ -188,6 +188,13 @@ static int do_psnr(FFFrameSync *fs)
>>          td.planeheight[c] = s->planeheight[c];
>>      }
>>
>> +    if (master->color_range != ref->color_range) {
>> +        av_log(ctx, AV_LOG_WARNING, "Warning: master and reference "
>> +               "frames use different color ranges (%s != %s)\n",
>> +               av_color_range_name(master->color_range),
>> +               av_color_range_name(ref->color_range));
>> +    }
>> +
>>      ff_filter_execute(ctx, compute_images_mse, &td, NULL,
>>                        FFMIN(s->planeheight[1], s->nb_threads));
>>
>> --
>> 2.39.2
>>
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