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authorNiklas Haas <git@haasn.xyz>2019-01-01 07:30:00 +0100
committerJan Ekström <jeebjp@gmail.com>2019-02-18 01:54:06 +0200
commit6179dcbb798aa9e3501af82ae46975e881d80626 (patch)
tree4ec798500982b8a3bf39bb4a03fe242cca5555d1 /DOCS
parent3fe882d4ae80fa060a71dad0d6d1605afcfe98b6 (diff)
downloadmpv-6179dcbb798aa9e3501af82ae46975e881d80626.tar.bz2
mpv-6179dcbb798aa9e3501af82ae46975e881d80626.tar.xz
vo_gpu: redesign peak detection algorithm
The previous approach of using an FIR with tunable hard threshold for scene changes had several problems: - the FIR involved annoying hard-coded buffer sizes, high VRAM usage, and the FIR sum was prone to numerical overflow which limited the number of frames we could average over. We also totally redesign the scene change detection. - the hard scene change detection was prone to both false positives and false negatives, each with their own (annoying) issues. Scrap this entirely and switch to a dual approach of using a simple single-pole IIR low pass filter to smooth out noise, while using a softer scene change curve (with tunable low and high thresholds), based on `smoothstep`. The IIR filter is extremely simple in its implementation and has an arbitrarily user-tunable cutoff frequency, while the smoothstep-based scene change curve provides a good, tunable tradeoff between adaptation speed and stability - without exhibiting either of the traditional issues associated with the hard cutoff. Another way to think about the new options is that the "low threshold" provides a margin of error within which we don't care about small fluctuations in the scene (which will therefore be smoothed out by the IIR filter).
Diffstat (limited to 'DOCS')
-rw-r--r--DOCS/interface-changes.rst1
-rw-r--r--DOCS/man/options.rst24
2 files changed, 25 insertions, 0 deletions
diff --git a/DOCS/interface-changes.rst b/DOCS/interface-changes.rst
index 7e723b9dbe..ce7e33176a 100644
--- a/DOCS/interface-changes.rst
+++ b/DOCS/interface-changes.rst
@@ -51,6 +51,7 @@ Interface changes
only using a single value (which previously just controlled the exponent).
The strength now linearly blends between the linear and nonlinear tone
mapped versions of a color.
+ - add --hdr-peak-decay-rate and --hdr-scene-threshold-low/high
--- mpv 0.29.0 ---
- drop --opensles-sample-rate, as --audio-samplerate should be used if desired
- drop deprecated --videotoolbox-format, --ff-aid, --ff-vid, --ff-sid,
diff --git a/DOCS/man/options.rst b/DOCS/man/options.rst
index 1c08917d7a..0f7007bf89 100644
--- a/DOCS/man/options.rst
+++ b/DOCS/man/options.rst
@@ -5245,6 +5245,30 @@ The following video options are currently all specific to ``--vo=gpu`` and
The special value ``auto`` (default) will enable HDR peak computation
automatically if compute shaders and SSBOs are supported.
+``--hdr-peak-decay-rate=<1.0..1000.0>``
+ The decay rate used for the HDR peak detection algorithm (default: 100.0).
+ This is only relevant when ``--hdr-compute-peak`` is enabled. Higher values
+ make the peak decay more slowly, leading to more stable values at the cost
+ of more "eye adaptation"-like effects (although this is mitigated somewhat
+ by ``--hdr-scene-threshold``). A value of 1.0 (the lowest possible) disables
+ all averaging, meaning each frame's value is used directly as measured,
+ but doing this is not recommended for "noisy" sources since it may lead
+ to excessive flicker. (In signal theory terms, this controls the time
+ constant "tau" of an IIR low pass filter)
+
+``--hdr-scene-threshold-low=<0..10000>``, ``--hdr-scene-threshold-high=<0..10000>``
+ The lower and upper thresholds (in cd/m^2) for a brightness difference to
+ be considered a scene change (default: 50 low, 200 high). This is only
+ relevant when ``--hdr-compute-peak`` is enabled. Normally, small
+ fluctuations in the frame brightness are compensated for by the peak
+ averaging mechanism, but for large jumps in the brightness this can result
+ in the frame remaining too bright or too dark for up to several seconds,
+ depending on the value of ``--hdr-peak-decay-rate``. To counteract this,
+ when the brightness between the running average and the current frame
+ exceeds the low threshold, mpv will make the averaging filter more
+ aggressive, up to the limit of the high threshold (at which point the
+ filter becomes instant).
+
``--tone-mapping-desaturate=<0.0..1.0>``
Apply desaturation for highlights (default: 0.75). The parameter controls
the strength of the desaturation curve. A value of 0.0 completely disables