[FFmpeg-devel] Enhancing/extending OpenEXR 'gamma' feature

Paul B Mahol onemda at gmail.com
Fri Aug 28 16:54:03 CEST 2015

On 8/28/15, Kevin Wheatley <kevin.j.wheatley at gmail.com> wrote:
> HI,
> I was wondering what others think about the option of extending the
> OpenEXR reader's gamma option to also include various transfer
> characteristic curves, potentially corresponding to the various
> AVCOL_TRC_* options, though I don't immediately have a need for all of
> them.
> In addition I could see the need for other curves like those of cinema
> camera vendor log curves, for instance Red, Sony, ARRI.
> From a user point of view I'd see a command line option specific to
> the EXR codec that would take a subset of the colour_trc options
> (bt709, etc) extended to include some camera transfer curves and it
> would apply the appropriate function prior to the encoding as
> AV_PIX_FMT_RGB48/64 as is done currently.
> I'm thinking the command line option would be called 'apply_trc'  or
> something similar.
> Why it is needed is simply that the gamma function isn't really
> sufficient for matching all the typical formats we see in production
> use.
> What would be nice would be to embed more colour adjustments prior to
> the truncation to integer values but that could be quite complex and
> may be better handled outside of ffmpeg.
> I've seen that there was a mention of something similar in the list
> archive, but could not find anything other than those emails.
> I'd be great full if any of the devs could comment on the idea before
> I start on the implementation.

Feel free to do it.

Note however that those various curves really belong to avfilter once
swscale supports float pixel format and exr decoder make use of it.

> Thanks
> Kevin
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