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Subject: media: media/doc: improve the SMPTE 2084 documentation
Author: Hans Verkuil <hansv...@cisco.com>
Date: Thu Jul 27 05:22:29 2017 -0400
Make note of the different luminance ranges between HDR and SDR.
Signed-off-by: Hans Verkuil <hansv...@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mche...@s-opensource.com>
Documentation/media/uapi/v4l/colorspaces-details.rst | 12 ++++++++++++
1 file changed, 12 insertions(+)
---
diff --git a/Documentation/media/uapi/v4l/colorspaces-details.rst
b/Documentation/media/uapi/v4l/colorspaces-details.rst
index 47d7d1915284..b5d551b9cc8f 100644
--- a/Documentation/media/uapi/v4l/colorspaces-details.rst
+++ b/Documentation/media/uapi/v4l/colorspaces-details.rst
@@ -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 [0â¦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.
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