https://www.imagemagick.org/discourse-server/viewtopic.php?f=3&t=32416

diff --git a/MagickCore/paint.c b/MagickCore/paint.c
index 975ca2fbccf54eba6f06b62683a7a5e5f7d8c1fe..78e5fffcf106de593748a51947db7a37c0d8ff8e 100644 (file)
--- a/MagickCore/paint.c
+++ b/MagickCore/paint.c
@@ -547,43 +547,46 @@ MagickExport MagickBooleanType GradientImage(Image *image,
       */
       sine=sin((double) DegreesToRadians(gradient->angle-90.0));
       cosine=cos((double) DegreesToRadians(gradient->angle-90.0));
-      distance=fabs((double) image->columns*cosine)+
-        fabs((double) image->rows*sine);
-      gradient->gradient_vector.x1=0.5*(image->columns-distance*cosine);
-      gradient->gradient_vector.y1=0.5*(image->rows-distance*sine);
-      gradient->gradient_vector.x2=0.5*(image->columns+distance*cosine);
-      gradient->gradient_vector.y2=0.5*(image->rows+distance*sine);
+      distance=fabs((double) (image->columns-1.0)*cosine)+
+        fabs((double) (image->rows-1.0)*sine);
+      gradient->gradient_vector.x1=0.5*((image->columns-1.0)-distance*cosine);
+      gradient->gradient_vector.y1=0.5*((image->rows-1.0)-distance*sine);
+      gradient->gradient_vector.x2=0.5*((image->columns-1.0)+distance*cosine);
+      gradient->gradient_vector.y2=0.5*((image->rows-1.0)+distance*sine);
     }
-  gradient->radii.x=(double) MagickMax(image->columns,image->rows)/2.0;
+  gradient->radii.x=(double) MagickMax((image->columns-1.0),(image->rows-1.0))/
+    2.0;
   gradient->radii.y=gradient->radii.x;
   artifact=GetImageArtifact(image,"gradient:extent");
   if (artifact != (const char *) NULL)
     {
       if (LocaleCompare(artifact,"Circle") == 0)
         {
-          gradient->radii.x=(double) MagickMax(image->columns,image->rows)/2.0;
+          gradient->radii.x=(double) MagickMax((image->columns-1.0),
+            (image->rows-1.0))/2.0;
           gradient->radii.y=gradient->radii.x;
         }
       if (LocaleCompare(artifact,"Diagonal") == 0)
         {
-          gradient->radii.x=(double) (sqrt(image->columns*image->columns+
-            image->rows*image->rows))/2.0;
+          gradient->radii.x=(double) (sqrt((image->columns-1.0)*
+            (image->columns-1.0)+(image->rows-1.0)*(image->rows-1.0)))/2.0;
           gradient->radii.y=gradient->radii.x;
         }
       if (LocaleCompare(artifact,"Ellipse") == 0)
         {
-          gradient->radii.x=(double) image->columns/2.0;
-          gradient->radii.y=(double) image->rows/2.0;
+          gradient->radii.x=(double) (image->columns-1.0)/2.0;
+          gradient->radii.y=(double) (image->rows-1.0)/2.0;
         }
       if (LocaleCompare(artifact,"Maximum") == 0)
         {
-          gradient->radii.x=(double) MagickMax(image->columns,image->rows)/2.0;
+          gradient->radii.x=(double) MagickMax((image->columns-1.0),
+            (image->rows-1.0))/2.0;
           gradient->radii.y=gradient->radii.x;
         }
       if (LocaleCompare(artifact,"Minimum") == 0)
         {
-          gradient->radii.x=(double) (MagickMin(image->columns,image->rows))/
-            2.0;
+          gradient->radii.x=(double) (MagickMin((image->columns-1.0),
+            (image->rows-1.0)))/2.0;
           gradient->radii.y=gradient->radii.x;
         }
     }