[FFmpeg-devel] [PATCH 1/2] avcodec: add photocd decoder

[Vittorio Giovara]

On Tue, Apr 7, 2020 at 7:58 AM Paul B Mahol <onemda at gmail.com> wrote:

> On 4/7/20, Vittorio Giovara <vittorio.giovara at gmail.com> wrote:
> > On Sat, Dec 22, 2018 at 3:18 PM Paul B Mahol <onemda at gmail.com> wrote:
> >
> >> On 12/22/18, Steinar H. Gunderson <steinar+ffmpeg at gunderson.no> wrote:
> >> > On Sat, Dec 22, 2018 at 09:04:26PM +0100, Paul B Mahol wrote:
> >> >> I can not accept internal conversion to RGB. This is subsampled
> format
> >> >> after all.
> >> >
> >> > Well, it's not Y'CbCr, so if so, you'd need to add a new AVPixelFormat
> >> value
> >> > (e.g. AV_PIX_FMT_YCC420P). I'm not sure what applications would do
> with
> >> it
> >> > except convert it to RGB, though. (You can't convert subsampled YCC to
> >> > subsampled Y'CbCr without upsampling, converting and then subsampling
> >> again,
> >> > which is obviously lossy.)
> >>
> >> Unacceptable, I'm not adding another yuv420p variant.
> >>
> >
> > Agreed, no need for another pixel format variant, but maybe you could
> just
> > leave the buffer as is and tag the color transfer with
> > AVCOL_TRC_IEC61966_2_1?
>
> Hmm, you sure that thing is exactly same what photocd uses?
> Is there a way to check it, in way that there is tool that converts
> that one to 709?
>

Sorry I'm unfamiliar with photocd to answer that, I just saw YCC mentioned
and remembered I saw it eslewhere.
If you have the tools to verify correct output, you could try with with
zimg/zscale, as it's one of the supported transfer.
Just make sure swscale is not inserted randomly in the filter chain.
-- 
Vittorio