From d8a3b10f45eb10fb34ce9da3a9a76e3bd8644e3d Mon Sep 17 00:00:00 2001 From: Niklas Haas Date: Fri, 9 Jun 2017 09:16:06 +0200 Subject: vo_opengl: add new HDR tone mapping algorithm MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit I call it `mobius` because apparently the form f(x) = (cx+a)/(dx+b) is called a Möbius transform, which is the algorithm this is based on. In the extremes it becomes `reinhard` (param=0.0 and `clip` (param=1.0), smoothly transitioning between the two depending on the parameter. This is a useful tone mapping algorithm since the tunable mobius transform allows the user to decide the trade-off between color accuracy and detail preservation on a continuous scale. The default of 0.3 is already far more accurate than `reinhard` while also being reasonably good at preserving highlights, without suffering from the overall brightness drop and color distortion of `hable`. For these reasons, make this the new default. Also expand and improve the documentation for these tone mapping functions. --- DOCS/man/options.rst | 28 ++++++++++++++++++++++++---- 1 file changed, 24 insertions(+), 4 deletions(-) (limited to 'DOCS/man/options.rst') diff --git a/DOCS/man/options.rst b/DOCS/man/options.rst index 7c8f602045..4d2be6ad66 100644 --- a/DOCS/man/options.rst +++ b/DOCS/man/options.rst @@ -4645,13 +4645,27 @@ The following video options are currently all specific to ``--vo=opengl`` and display. Valid values are: clip - Hard-clip any out-of-range values. + Hard-clip any out-of-range values. Use this when you care about + perfect color accuracy for in-range values at the cost of completely + distorting out-of-range values. Not generally recommended. + mobius + Generalization of Reinhard to a Möbius transform with linear section. + Smoothly maps out-of-range values while retaining contrast and colors + for in-range material as much as possible. Use this when you care about + color accuracy more than detail preservation. This is somewhere in + between ``clip`` and ``reinhard``, depending on the value of + ``--tone-mapping-param``. (default) reinhard Reinhard tone mapping algorithm. Very simple continuous curve. - Preserves dynamic range and peak but uses nonlinear contrast. + Preserves overall image brightness but uses nonlinear contrast, which + results in flattening of details and degradation in color accuracy. hable - Similar to ``reinhard`` but preserves dark contrast better (slightly - sigmoidal). Developed by John Hable for use in video games. (default) + Similar to ``reinhard`` but preserves both dark and bright details + better (slightly sigmoidal), at the cost of slightly darkening + everything. Developed by John Hable for use in video games. Use this + when you care about detail preservation more than color/brightness + accuracy. This is roughly equivalent to + ``--hdr-tone-mapping=reinhard --tone-mapping-param=0.24``. gamma Fits a logarithmic transfer between the tone curves. linear @@ -4662,6 +4676,12 @@ The following video options are currently all specific to ``--vo=opengl`` and Set tone mapping parameters. Ignored if the tone mapping algorithm is not tunable. This affects the following tone mapping algorithms: + mobius + Specifies the transition point from linear to mobius transform. Every + value below this point is guaranteed to be mapped 1:1. The higher the + value, the more accurate the result will be, at the cost of losing + bright details. Defaults to 0.3, which due to the steep initial slope + still preserves in-range colors fairly accurately. reinhard Specifies the local contrast coefficient at the display peak. Defaults to 0.5, which means that in-gamut values will be about half as bright -- cgit v1.2.3