[FFmpeg-devel] [PATCH] avcodec/exr: add cineon lin2log trc

[Kevin Wheatley]

On Fri, Mar 6, 2020 at 10:19 AM Hendrik Leppkes <h.leppkes at gmail.com> wrote:
> AVColorTransferCharacteristic should follow ISO/IEC 23001-8 and its
> following standards (ISO/IEC 23091 I believe). Not sure we have a
> solution for specialized variants, but adding one right there would
> collide with the next addition to the standard...

Agreed, A publicly "aligned twin text" version is available as ITU-T
H.273 https://www.itu.int/rec/T-REC-H.273-201612-I/en shows that value
is 'reserved'.

I would also suggest that there are a few implementations of the
Cineon log to lin conversion and as such I'd reject it as is.
You will need to pass in the parameters for the various variables
white, black etc. You will also need to add a parameter for the
density per code value constant (0.002 by default convention).
Not all implementations use a gain scaling, though strictly these are
no longer "Cineon" per se, but you will end up with needing various
camera vendor equivalents. This would result in a large proliferation
of equations, which I don't believe are core to the FFmpeg code.

You would perhaps be better creating a specialist filter and
implementing it using OCIO (as suggested
https://github.com/AcademySoftwareFoundation/tac/tree/master/gsoc), or
extending the current 3D LUT code to read Cinespace or other 3D LUT
formats that support a pre-shaper and handle the float->integer
conversion that way.

Kevin