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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>
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@ -793,3 +793,15 @@ Transfer function:
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Inverse Transfer function:
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L = (max(L':sup:`1/m2` - c1, 0) / (c2 - c3 *
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L'\ :sup:`1/m2`))\ :sup:`1/m1`
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Take care when converting between this transfer function and non-HDR transfer
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functions: the linear RGB values [0…1] of HDR content map to a luminance range
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of 0 to 10000 cd/m\ :sup:`2` whereas the linear RGB values of non-HDR (aka
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Standard Dynamic Range or SDR) map to a luminance range of 0 to 100 cd/m\ :sup:`2`.
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To go from SDR to HDR you will have to divide L by 100 first. To go in the other
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direction you will have to multiply L by 100. Of course, this clamps all
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luminance values over 100 cd/m\ :sup:`2` to 100 cd/m\ :sup:`2`.
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There are better methods, see e.g. :ref:`colimg` for more in-depth information
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about this.
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