avfilter: add threshold filter

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

Changelog

@@ -19,6 +19,7 @@ version <next>:
 - Sample Dump eXchange demuxer
 - abitscope multimedia filter
 - Scenarist Closed Captions demuxer and muxer
+- threshold filter
 
 version 3.2:
 - libopenmpt demuxer

doc/filters.texi

@@ -13192,6 +13192,63 @@ PAL output (25i):
 16p: 33333334
 @end example
 
+@section threshold
+
+Apply threshold effect to video stream.
+
+This filter needs four video streams to perform thresholding.
+First stream is stream we are filtering.
+Second stream is holding threshold values, third stream is holding min values,
+and last, fourth stream is holding max values.
+
+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.
+@end table
+
+For example if first stream pixel's component value is less then threshold value
+of pixel component from 2nd threshold stream, third stream value will picked,
+otherwise fourth stream pixel component value will be picked.
+
+Using color source filter one can perform various types of thresholding:
+
+@subsection Examples
+
+@itemize
+@item
+Binary threshold, using gray color as threshold:
+@example
+ffmpeg -i 320x240.avi -f lavfi -i color=gray -f lavfi -i color=black -f lavfi -i color=white -lavfi threshold output.avi
+@end example
+
+@item
+Inverted binary threshold, using gray color as threshold:
+@example
+ffmpeg -i 320x240.avi -f lavfi -i color=gray -f lavfi -i color=white -f lavfi -i color=black -lavfi threshold output.avi
+@end example
+
+@item
+Truncate binary threshold, using gray color as threshold:
+@example
+ffmpeg -i 320x240.avi -f lavfi -i color=gray -i 320x240.avi -f lavfi -i color=gray -lavfi threshold output.avi
+@end example
+
+@item
+Threshold to zero, using gray color as threshold:
+@example
+ffmpeg -i 320x240.avi -f lavfi -i color=gray -f lavfi -i color=white -i 320x240.avi -lavfi threshold output.avi
+@end example
+
+@item
+Inverted threshold to zero, using gray color as threshold:
+@example
+ffmpeg -i 320x240.avi -f lavfi -i color=gray -i 320x240.avi -f lavfi -i color=white -lavfi threshold output.avi
+@end example
+@end itemize
+
 @section thumbnail
 Select the most representative frame in a given sequence of consecutive frames.
 

libavfilter/Makefile

@@ -289,6 +289,7 @@ OBJS-$(CONFIG_SWAPRECT_FILTER)               += vf_swaprect.o
 OBJS-$(CONFIG_SWAPUV_FILTER)                 += vf_swapuv.o
 OBJS-$(CONFIG_TBLEND_FILTER)                 += vf_blend.o dualinput.o framesync.o
 OBJS-$(CONFIG_TELECINE_FILTER)               += vf_telecine.o
+OBJS-$(CONFIG_THRESHOLD_FILTER)              += vf_threshold.o
 OBJS-$(CONFIG_THUMBNAIL_FILTER)              += vf_thumbnail.o
 OBJS-$(CONFIG_TILE_FILTER)                   += vf_tile.o
 OBJS-$(CONFIG_TINTERLACE_FILTER)             += vf_tinterlace.o

libavfilter/allfilters.c

@@ -304,6 +304,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER(SWAPUV,         swapuv,         vf);
     REGISTER_FILTER(TBLEND,         tblend,         vf);
     REGISTER_FILTER(TELECINE,       telecine,       vf);
+    REGISTER_FILTER(THRESHOLD,      threshold,      vf);
     REGISTER_FILTER(THUMBNAIL,      thumbnail,      vf);
     REGISTER_FILTER(TILE,           tile,           vf);
     REGISTER_FILTER(TINTERLACE,     tinterlace,     vf);

libavfilter/version.h

@@ -30,7 +30,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVFILTER_VERSION_MAJOR   6
-#define LIBAVFILTER_VERSION_MINOR  71
+#define LIBAVFILTER_VERSION_MINOR  72
 #define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \