[FFmpeg-devel] [PATCH] avfilter/vf_scale: set RGB to always be full range

[Michael Niedermayer]

On Wed, Sep 16, 2020 at 12:16:43AM +0300, Jan Ekström wrote:
> This value - while it looks like the actual range of the content -
> is nothing but the internal value of swscale.
> 
> Thus, if we have RGB content, force the value to 1. Swscale will
> ignore it, but at least the value of the output AVFrame will now
> properly be "full range" instead of "limited range", as it is right
> now.
> ---
>  libavfilter/vf_scale.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/libavfilter/vf_scale.c b/libavfilter/vf_scale.c
> index 58eee96744..12df27edf4 100644
> --- a/libavfilter/vf_scale.c
> +++ b/libavfilter/vf_scale.c
[...]
> @@ -768,7 +777,15 @@ scale:
>          else if (in_range != AVCOL_RANGE_UNSPECIFIED)
>              in_full  = (in_range == AVCOL_RANGE_JPEG);
>          if (scale->out_range != AVCOL_RANGE_UNSPECIFIED)
> +            // note: this can be silently overridden by
> +            //       sws_setColorspaceDetails for non-YCbCr formats
>              out_full = (scale->out_range == AVCOL_RANGE_JPEG);
> +        else if (out_desc->flags & AV_PIX_FMT_FLAG_RGB)
> +            // the range values received from swscale are its internal
> +            // identifiers, and will not be nonzero for any sort of RGB.
> +            // thus, if we do not set it to nonzero ourselves, this will
> +            // be incorrect.
> +            out_full = 1;

Does anything document the meaning of range or AVCOL_RANGE for RGB ?
The enum is documented as "MPEG vs JPEG YUV range."

What is limited range RGB ? what would the ranges of R,G,B be and where
is that specified ?

That said, changing it to full range for RGB as done by this patch is
probably ok if it helps some code (for example allows simplifications)

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Complexity theory is the science of finding the exact solution to an
approximation. Benchmarking OTOH is finding an approximation of the exact
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 195 bytes
Desc: not available
URL: <https://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20200916/b6a8372b/attachment.sig>