From c795e7d0900fa815bc7df72bd1db816764132935 Mon Sep 17 00:00:00 2001 From: Hans Verkuil Date: Thu, 27 Jul 2017 05:22:29 -0400 Subject: [PATCH] media: media/doc: improve the SMPTE 2084 documentation Make note of the different luminance ranges between HDR and SDR. Signed-off-by: Hans Verkuil Signed-off-by: Mauro Carvalho Chehab --- 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 47d7d19..b5d551b 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 [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. -- 2.7.4