avfilter: Add colorconstancy filter

Signed-off-by: Mina <minasamy_@hotmail.com>

Changelog

@@ -15,6 +15,7 @@ version <next>:
 - vc1 decoder is now bit-exact
 - ATRAC9 decoder
 - lensfun wrapper filter
+- colorconstancy filter
 
 
 version 4.0:

MAINTAINERS

@@ -332,6 +332,7 @@ Filters:
   vf_bwdif                              Thomas Mundt (CC <thomas.mundt@hr.de>)
   vf_chromakey.c                        Timo Rothenpieler
   vf_colorchannelmixer.c                Paul B Mahol
+  vf_colorconstancy.c                   Mina Sami    (CC <minas.gorgy@gmail.com>)
   vf_colorbalance.c                     Paul B Mahol
   vf_colorkey.c                         Timo Rothenpieler
   vf_colorlevels.c                      Paul B Mahol

doc/filters.texi

@@ -9940,6 +9940,47 @@ gradfun=radius=8
 
 @end itemize
 
+@section greyedge
+A color constancy variation filter which estimates scene illumination via grey edge algorithm
+and corrects the scene colors accordingly.
+
+See: @url{https://staff.science.uva.nl/th.gevers/pub/GeversTIP07.pdf}
+
+The filter accepts the following options:
+
+@table @option
+@item difford
+The order of differentiation to be applied on the scene. Must be chosen in the range
+[0,2] and default value is 1.
+
+@item minknorm
+The Minkowski parameter to be used for calculating the Minkowski distance. Must
+be chosen in the range [0,65535] and default value is 1. Set to 0 for getting
+max value instead of calculating Minkowski distance.
+
+@item sigma
+The standard deviation of Gaussian blur to be applied on the scene. Must be
+chosen in the range [0,1024.0] and default value = 1. Sigma can't be set to 0
+if @var{difford} is greater than 0.
+@end table
+
+@subsection Examples
+@itemize
+
+@item
+Grey Edge:
+@example
+greyedge=difford=1:minknorm=5:sigma=2
+@end example
+
+@item
+Max Edge:
+@example
+greyedge=difford=1:minknorm=0:sigma=2
+@end example
+
+@end itemize
+
 @anchor{haldclut}
 @section haldclut
 

libavfilter/Makefile

@@ -228,6 +228,7 @@ OBJS-$(CONFIG_FSPP_FILTER)                   += vf_fspp.o
 OBJS-$(CONFIG_GBLUR_FILTER)                  += vf_gblur.o
 OBJS-$(CONFIG_GEQ_FILTER)                    += vf_geq.o
 OBJS-$(CONFIG_GRADFUN_FILTER)                += vf_gradfun.o
+OBJS-$(CONFIG_GREYEDGE_FILTER)               += vf_colorconstancy.o
 OBJS-$(CONFIG_HALDCLUT_FILTER)               += vf_lut3d.o framesync.o
 OBJS-$(CONFIG_HFLIP_FILTER)                  += vf_hflip.o
 OBJS-$(CONFIG_HISTEQ_FILTER)                 += vf_histeq.o

libavfilter/allfilters.c

@@ -217,6 +217,7 @@ extern AVFilter ff_vf_fspp;
 extern AVFilter ff_vf_gblur;
 extern AVFilter ff_vf_geq;
 extern AVFilter ff_vf_gradfun;
+extern AVFilter ff_vf_greyedge;
 extern AVFilter ff_vf_haldclut;
 extern AVFilter ff_vf_hflip;
 extern AVFilter ff_vf_histeq;