avfilter: add unpremultiply filter

Signed-off-by: Paul B Mahol <onemda@gmail.com>

Changelog

@@ -29,6 +29,7 @@ version <next>:
 - limiter video filter
 - libvmaf video filter
 - Dolby E decoder and SMPTE 337M demuxer
+- unpremultiply video filter
 
 version 3.3:
 - CrystalHD decoder moved to new decode API

doc/filters.texi

@@ -14532,6 +14532,25 @@ ffmpeg -i INPUT -vf trim=duration=1
 
 @end itemize
 
+@section unpremultiply
+Apply alpha unpremultiply effect to input video stream using first plane
+of second stream as alpha.
+
+Both streams must have same dimensions and same pixel format.
+
+The filter accepts the following option:
+
+@table @option
+@item planes
+Set which planes will be processed, unprocessed planes will be copied.
+By default value 0xf, all planes will be processed.
+
+If the format has 1 or 2 components, then luma is bit 0.
+If the format has 3 or 4 components:
+for RGB formats bit 0 is green, bit 1 is blue and bit 2 is red;
+for YUV formats bit 0 is luma, bit 1 is chroma-U and bit 2 is chroma-V.
+If present, the alpha channel is always the last bit.
+@end table
 
 @anchor{unsharp}
 @section unsharp

libavfilter/Makefile

@@ -314,6 +314,7 @@ OBJS-$(CONFIG_TILE_FILTER)                   += vf_tile.o
 OBJS-$(CONFIG_TINTERLACE_FILTER)             += vf_tinterlace.o
 OBJS-$(CONFIG_TRANSPOSE_FILTER)              += vf_transpose.o
 OBJS-$(CONFIG_TRIM_FILTER)                   += trim.o
+OBJS-$(CONFIG_UNPREMULTIPLY_FILTER)          += vf_premultiply.o framesync2.o
 OBJS-$(CONFIG_UNSHARP_FILTER)                += vf_unsharp.o
 OBJS-$(CONFIG_USPP_FILTER)                   += vf_uspp.o
 OBJS-$(CONFIG_VAGUEDENOISER_FILTER)          += vf_vaguedenoiser.o

libavfilter/allfilters.c

@@ -325,6 +325,7 @@ static void register_all(void)
     REGISTER_FILTER(TINTERLACE,     tinterlace,     vf);
     REGISTER_FILTER(TRANSPOSE,      transpose,      vf);
     REGISTER_FILTER(TRIM,           trim,           vf);
+    REGISTER_FILTER(UNPREMULTIPLY,  unpremultiply,  vf);
     REGISTER_FILTER(UNSHARP,        unsharp,        vf);
     REGISTER_FILTER(USPP,           uspp,           vf);
     REGISTER_FILTER(VAGUEDENOISER,  vaguedenoiser,  vf);

libavfilter/version.h

@@ -30,7 +30,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVFILTER_VERSION_MAJOR   6
-#define LIBAVFILTER_VERSION_MINOR  95
+#define LIBAVFILTER_VERSION_MINOR  96
 #define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \