lavfi: add vignette filter.

Changelog

@@ -59,6 +59,7 @@ version <next>:
 - VC-1 interlaced B-frame support
 - support for WavPack muxing (raw and in Matroska)
 - XVideo output device
+- vignette filter
 
 
 version 1.2:

doc/filters.texi

@@ -6950,6 +6950,109 @@ For example, to vertically flip a video with @command{ffmpeg}:
 ffmpeg -i in.avi -vf "vflip" out.avi
 @end example
 
+@section vignette
+
+Make or reverse a natural vignetting effect.
+
+The filter accepts the following options:
+
+@table @option
+@item angle, a
+Set lens angle expression as a number of radians.
+
+The value is clipped in the @code{[0,PI/2]} range.
+
+Default value: @code{"PI/5"}
+
+@item x0
+@item y0
+Set center coordinates expressions. Respectively @code{"w/2"} and @code{"h/2"}
+by default.
+
+@item mode
+Set forward/backward mode.
+
+Available modes are:
+@table @samp
+@item forward
+The larger the distance from the central point, the darker the image becomes.
+
+@item backward
+The larger the distance from the central point, the brighter the image becomes.
+This can be used to reverse a vignette effect, though there is no automatic
+detection to extract the lens @option{angle} and other settings (yet). It can
+also be used to create a burning effect.
+@end table
+
+Default value is @samp{forward}.
+
+@item eval
+Set evaluation mode for the expressions (@option{angle}, @option{x0}, @option{y0}).
+
+It accepts the following values:
+@table @samp
+@item init
+Evaluate expressions only once during the filter initialization.
+
+@item frame
+Evaluate expressions for each incoming frame. This is way slower than the
+@samp{init} mode since it requires all the scalers to be re-computed, but it
+allows advanced dynamic expressions.
+@end table
+
+Default value is @samp{init}.
+
+@item dither
+Set dithering to reduce the circular banding effects. Default is @code{1}
+(enabled).
+@end table
+
+@subsection Expressions
+
+The @option{alpha}, @option{x0} and @option{y0} expressions can contain the
+following parameters.
+
+@table @option
+@item w
+@item h
+input width and height
+
+@item n
+the number of input frame, starting from 0
+
+@item pts
+the PTS (Presentation TimeStamp) time of the filtered video frame, expressed in
+@var{TB} units, NAN if undefined
+
+@item r
+frame rate of the input video, NAN if the input frame rate is unknown
+
+@item t
+the PTS (Presentation TimeStamp) of the filtered video frame,
+expressed in seconds, NAN if undefined
+
+@item tb
+time base of the input video
+@end table
+
+
+@subsection Examples
+
+@itemize
+@item
+Apply simple strong vignetting effect:
+@example
+vignette=PI/4
+@end example
+
+@item
+Make a flickering vignetting:
+@example
+vignette='PI/4+random(1)*PI/50':eval=frame
+@end example
+
+@end itemize
+
 @anchor{yadif}
 @section yadif
 

libavfilter/Makefile

@@ -191,6 +191,7 @@ OBJS-$(CONFIG_UNSHARP_FILTER)                += vf_unsharp.o
 OBJS-$(CONFIG_VFLIP_FILTER)                  += vf_vflip.o
 OBJS-$(CONFIG_VIDSTABDETECT_FILTER)          += vidstabutils.o vf_vidstabdetect.o
 OBJS-$(CONFIG_VIDSTABTRANSFORM_FILTER)       += vidstabutils.o vf_vidstabtransform.o
+OBJS-$(CONFIG_VIGNETTE_FILTER)               += vf_vignette.o
 OBJS-$(CONFIG_YADIF_FILTER)                  += vf_yadif.o
 OBJS-$(CONFIG_ZMQ_FILTER)                    += f_zmq.o
 

libavfilter/allfilters.c

@@ -188,6 +188,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER(VFLIP,          vflip,          vf);
     REGISTER_FILTER(VIDSTABDETECT,  vidstabdetect,  vf);
     REGISTER_FILTER(VIDSTABTRANSFORM, vidstabtransform, vf);
+    REGISTER_FILTER(VIGNETTE,       vignette,       vf);
     REGISTER_FILTER(YADIF,          yadif,          vf);
     REGISTER_FILTER(ZMQ,            zmq,            vf);
 

libavfilter/version.h

@@ -30,7 +30,7 @@
 #include "libavutil/avutil.h"
 
 #define LIBAVFILTER_VERSION_MAJOR  3
-#define LIBAVFILTER_VERSION_MINOR  72
+#define LIBAVFILTER_VERSION_MINOR  73
 #define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \