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media: media/doc: improve the SMPTE 2084 documentation 

Make note of the different luminance ranges between HDR and SDR.

Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
hifive-unleashed-5.1
Hans Verkuil 2017-07-27 05:22:29 -04:00 committed by Mauro Carvalho Chehab
parent fb98531e89
commit c795e7d090
1 changed files with 12 additions and 0 deletions
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12
Documentation/media/uapi/v4l/colorspaces-details.rst
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@ -793,3 +793,15 @@ Transfer function:
Inverse Transfer function:
L = (max(L':sup:`1/m2` - c1, 0) / (c2 - c3 *
L'\ :sup:`1/m2`))\ :sup:`1/m1`
Take care when converting between this transfer function and non-HDR transfer
functions: the linear RGB values [0…1] of HDR content map to a luminance range
of 0 to 10000 cd/m\ :sup:`2` whereas the linear RGB values of non-HDR (aka
Standard Dynamic Range or SDR) map to a luminance range of 0 to 100 cd/m\ :sup:`2`.
To go from SDR to HDR you will have to divide L by 100 first. To go in the other
direction you will have to multiply L by 100. Of course, this clamps all
luminance values over 100 cd/m\ :sup:`2` to 100 cd/m\ :sup:`2`.
There are better methods, see e.g. :ref:`colimg` for more in-depth information
about this.