Add tonemap filter

Based off mpv automatic tonemapping capabilities.
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

doc/filters.texi

@@ -14442,6 +14442,113 @@ Vertical low-pass filtering can only be enabled for @option{mode}
 
 @end table
 
+@section tonemap
+Tone map colors from different dynamic ranges.
+
+This filter expects data in single precision floating point, as it needs to
+operate on (and can output) out-of-range values. Another filter, such as
+@ref{zscale}, is needed to convert the resulting frame to a usable format.
+
+The tonemapping algorithms implemented only work on linear light, so input
+data should be linearized beforehand (and possibly correctly tagged).
+
+@example
+ffmpeg -i INPUT -vf zscale=transfer=linear,tonemap=clip,zscale=transfer=bt709,format=yuv420p OUTPUT
+@end example
+
+@subsection Options
+The filter accepts the following options.
+
+@table @option
+@item tonemap
+Set the tone map algorithm to use.
+
+Possible values are:
+@table @var
+@item none
+Do not apply any tone map, only desaturate overbright pixels.
+
+@item clip
+Hard-clip any out-of-range values. Use it for perfect color accuracy for
+in-range values, while distorting out-of-range values.
+
+@item linear
+Stretch the entire reference gamut to a linear multiple of the display.
+
+@item gamma
+Fit a logarithmic transfer between the tone curves.
+
+@item reinhard
+Preserve overall image brightness with a simple curve, using nonlinear
+contrast, which results in flattening details and degrading color accuracy.
+
+@item hable
+Peserve both dark and bright details better than @var{reinhard}, at the cost
+of slightly darkening everything. Use it when detail preservation is more
+important than color and brightness accuracy.
+
+@item mobius
+Smoothly map out-of-range values, while retaining contrast and colors for
+in-range material as much as possible. Use it when color accuracy is more
+important than detail preservation.
+@end table
+
+Default is none.
+
+@item param
+Tune the tone mapping algorithm.
+
+This affects the following algorithms:
+@table @var
+@item none
+Ignored.
+
+@item linear
+Specifies the scale factor to use while stretching.
+Default to 1.0.
+
+@item gamma
+Specifies the exponent of the function.
+Default to 1.8.
+
+@item clip
+Specify an extra linear coefficient to multiply into the signal before clipping.
+Default to 1.0.
+
+@item reinhard
+Specify the local contrast coefficient at the display peak.
+Default to 0.5, which means that in-gamut values will be about half as bright
+as when clipping.
+
+@item hable
+Ignored.
+
+@item mobius
+Specify 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.
+Default to 0.3, which due to the steep initial slope still preserves in-range
+colors fairly accurately.
+@end table
+
+@item desat
+Apply desaturation for highlights that exceed this level of brightness. The
+higher the parameter, the more color information will be preserved. This
+setting helps prevent unnaturally blown-out colors for super-highlights, by
+(smoothly) turning into white instead. This makes images feel more natural,
+at the cost of reducing information about out-of-range colors.
+
+The default of 2.0 is somewhat conservative and will mostly just apply to
+skies or directly sunlit surfaces. A setting of 0.0 disables this option.
+
+This option works only if the input frame has a supported color tag.
+
+@item peak
+Override signal/nominal/reference peak with this value. Useful when the
+embedded peak information in display metadata is not reliable or when tone
+mapping from a lower range to a higher range.
+@end table
+
 @section transpose
 
 Transpose rows with columns in the input video and optionally flip it.
@@ -15627,6 +15734,7 @@ zoompan=z='min(max(zoom,pzoom)+0.0015,1.5)':d=1:x='iw/2-(iw/zoom/2)':y='ih/2-(ih
 @end example
 @end itemize
 
+@anchor{zscale}
 @section zscale
 Scale (resize) the input video, using the z.lib library:
 https://github.com/sekrit-twc/zimg.

libavfilter/Makefile

@@ -314,6 +314,7 @@ OBJS-$(CONFIG_THUMBNAIL_FILTER)              += vf_thumbnail.o
 OBJS-$(CONFIG_TILE_FILTER)                   += vf_tile.o
 OBJS-$(CONFIG_TINTERLACE_FILTER)             += vf_tinterlace.o
 OBJS-$(CONFIG_TLUT2_FILTER)                  += vf_lut2.o framesync2.o
+OBJS-$(CONFIG_TONEMAP_FILTER)                += vf_tonemap.o
 OBJS-$(CONFIG_TRANSPOSE_FILTER)              += vf_transpose.o
 OBJS-$(CONFIG_TRIM_FILTER)                   += trim.o
 OBJS-$(CONFIG_UNPREMULTIPLY_FILTER)          += vf_premultiply.o framesync2.o

libavfilter/allfilters.c

@@ -325,6 +325,7 @@ static void register_all(void)
     REGISTER_FILTER(TILE,           tile,           vf);
     REGISTER_FILTER(TINTERLACE,     tinterlace,     vf);
     REGISTER_FILTER(TLUT2,          tlut2,          vf);
+    REGISTER_FILTER(TONEMAP,        tonemap,        vf);
     REGISTER_FILTER(TRANSPOSE,      transpose,      vf);
     REGISTER_FILTER(TRIM,           trim,           vf);
     REGISTER_FILTER(UNPREMULTIPLY,  unpremultiply,  vf);

libavfilter/version.h

@@ -30,7 +30,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVFILTER_VERSION_MAJOR   6
-#define LIBAVFILTER_VERSION_MINOR  98
+#define LIBAVFILTER_VERSION_MINOR  99
 #define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \