[FFmpeg-devel] [PATCH] Add a gamma flag to exr loader to avoid banding

Ronald S. Bultje rsbultje at gmail.com
Tue Apr 29 15:18:38 CEST 2014


On Tue, Apr 29, 2014 at 2:49 AM, Jimmy Christensen <jimmy at ghost.dk> wrote:

> 'm not sure that I like that it's default with gamma 2.2. Personally I
> would rather have it defaults to gamma 1.0 (no changes).

The gamma here is a little different from what you probably think it is,
it's the linear XYZ (that's the actual perceived rays of light shooting in
your eye as a scientific metric) vs. exponential RGB/YUV (which are just
matrix transformations of each other), such as sRGB or bt709 or whatever.
It's not the gamma _over_ the non-linear YUV/RGB (which was already
non-linear in itself), which is the kind of operation that you get when you
apply a gamma in e.g. gimp or photoshop on an image.

For typical gamma values for colorspaces, see e.g.
http://www.brucelindbloom.com/index.html?Eqn_RGB_to_XYZ.html - 2.2 is a
pretty typical default.


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