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

[Kevin Wheatley]

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.

Thanks

Kevin