diff -up ImageMagick-6.7.8-9/magick/quantize.c.quantize ImageMagick-6.7.8-9/magick/quantize.c

--- ImageMagick-6.7.8-9/magick/quantize.c.quantize	2012-08-09 02:12:12.000000000 +0200

+++ ImageMagick-6.7.8-9/magick/quantize.c	2018-10-23 14:16:48.484639782 +0200

@@ -333,7 +333,9 @@ static MagickBooleanType

   SetGrayscaleImage(Image *);

 static size_t

-  DefineImageColormap(Image *,CubeInfo *,NodeInfo *);

+  DefineImageColormap(Image *,CubeInfo *,NodeInfo *),

+  QuantizeErrorFlatten(const Image *,const CubeInfo *,const NodeInfo *,

+    const ssize_t,const size_t,MagickRealType *);

 static void

   ClosestColor(const Image *,CubeInfo *,const NodeInfo *),

@@ -2882,6 +2884,66 @@ MagickExport MagickBooleanType QuantizeI

 %                                                                             %

 %                                                                             %

 %                                                                             %

++   Q u a n t i z e E r r o r F l a t t e n                                   %

+%                                                                             %

+%                                                                             %

+%                                                                             %

+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

+%

+%  QuantizeErrorFlatten() traverses the color cube and flattens the quantization

+%  error into a sorted array.  This accelerates the color reduction process.

+%

+%  Contributed by Yoya.

+%

+%  The format of the QuantizeImages method is:

+%

+%      size_t QuantizeErrorFlatten(const Image *image,const CubeInfo *cube_info,

+%        const NodeInfo *node_info,const ssize_t offset,const size_t extent,

+%        MagickRealType *quantize_error)

+%

+%  A description of each parameter follows.

+%

+%    o image: the image.

+%

+%    o cube_info: A pointer to the Cube structure.

+%

+%    o node_info: pointer to node in color cube tree that is current pointer.

+%

+%    o offset: quantize error offset.

+%

+%    o extent: quantize error offset maximum limit.

+%

+%    o quantize_error: the quantization error vector.

+%

+*/

+static size_t QuantizeErrorFlatten(const Image *image,const CubeInfo *cube_info,

+  const NodeInfo *node_info,const ssize_t offset,const size_t extent,

+  MagickRealType *quantize_error)

+{

+  register ssize_t

+    i;

+

+  size_t

+    n,

+    number_children;

+

+  if (offset >= (ssize_t) extent)

+    return(0);

+  quantize_error[offset]=node_info->quantize_error;

+  n=1;

+  number_children=cube_info->associate_alpha == MagickFalse ? 8UL : 16UL;

+  for (i=0; i < (ssize_t) number_children ; i++)

+    if (node_info->child[i] != (NodeInfo *) NULL)

+      n+=QuantizeErrorFlatten(image,cube_info,node_info->child[i],offset+n,

+        extent,quantize_error);

+  return(n);

+}

+ 

+/*

+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

+%                                                                             %

+%                                                                             %

+%                                                                             %

 +   R e d u c e                                                               %

 %                                                                             %

 %                                                                             %

@@ -2988,6 +3050,22 @@ static void Reduce(const Image *image,Cu

 %    o cube_info: A pointer to the Cube structure.

 %

 */

+

+static int MagickRealTypeCompare(const void *error_p,const void *error_q)

+{

+  MagickRealType

+    *p,

+    *q;

+

+  p=(MagickRealType *) error_p;

+  q=(MagickRealType *) error_q;

+  if (*p > *q)

+    return(1);

+  if (fabs((double) (*q-*p)) <= MagickEpsilon)

+    return(0);

+  return(-1);

+}

+

 static void ReduceImageColors(const Image *image,CubeInfo *cube_info)

 {

 #define ReduceImageTag  "Reduce/Image"

@@ -3002,6 +3080,28 @@ static void ReduceImageColors(const Imag

     span;

   cube_info->next_threshold=0.0;

+  if (cube_info->colors > cube_info->maximum_colors)

+    {

+      MagickRealType

+        *quantize_error;

+

+      /*

+        Enable rapid reduction of the number of unique colors.

+      */

+      quantize_error=(MagickRealType *) AcquireQuantumMemory(cube_info->nodes,

+        sizeof(*quantize_error));

+      if (quantize_error != (MagickRealType *) NULL)

+        {

+          (void) QuantizeErrorFlatten(image,cube_info,cube_info->root,0,

+            cube_info->nodes,quantize_error);

+          qsort(quantize_error,cube_info->nodes,sizeof(MagickRealType),

+            MagickRealTypeCompare);

+          cube_info->next_threshold=quantize_error[cube_info->nodes-

+            cube_info->maximum_colors];

+          quantize_error=(MagickRealType *) RelinquishMagickMemory(

+            quantize_error);

+        }

+  }

   for (span=cube_info->colors; cube_info->colors > cube_info->maximum_colors; )

   {

     cube_info->pruning_threshold=cube_info->next_threshold;