diff --git a/ChangeLog b/ChangeLog
index f357dce35a..29d6612918 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2005-07-14  Sven Neumann  <sven@gimp.org>
+
+	* app/paint-funcs/paint-funcs.[ch]: added erode_region() and
+	dilate_region(). Less general than thin_region() and fatten_region()
+	but a little faster.
+
+	* app/base/siox.c: use the new functions.
+
 2005-07-14  Michael Natterer  <mitch@gimp.org>
 
 	* app/widgets/Makefile.am
diff --git a/app/base/siox.c b/app/base/siox.c
index 00a1de6108..47f18edf48 100644
--- a/app/base/siox.c
+++ b/app/base/siox.c
@@ -16,6 +16,8 @@
  * by Gerald Friedland <fland@inf.fu-berlin.de>
  * and Kristian Jantz <jantz@inf.fu-berlin.de>.
  *
+ * Adapted for GIMP by Sven Neumann <sven@gimp.org>
+ *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
  * as published by the Free Software Foundation; either version 2
@@ -649,8 +651,7 @@ erode_mask (TileManager *mask,
 
   pixel_region_init (&region, mask, x, y, width, height, TRUE);
 
-  /* inefficient */
-  thin_region (&region, 1, 1, TRUE);
+  erode_region (&region);
 }
 
 static void
@@ -664,8 +665,7 @@ dilate_mask (TileManager *mask,
 
   pixel_region_init (&region, mask, x, y, width, height, TRUE);
 
-  /* inefficient */
-  fatten_region (&region, 1, 1);
+  dilate_region (&region);
 }
 
 static void
diff --git a/app/paint-funcs/paint-funcs.c b/app/paint-funcs/paint-funcs.c
index 5eaea8a86c..e1fbfac335 100644
--- a/app/paint-funcs/paint-funcs.c
+++ b/app/paint-funcs/paint-funcs.c
@@ -3350,7 +3350,7 @@ smooth_region (PixelRegion *region)
           memcpy (buf[2], buf[1], width + 2);
         }
 
-      for (x = 0 ; x < width; x++) /* render scan line */
+      for (x = 0 ; x < width; x++)
         {
           gint value = (buf[0][x] + buf[0][x+1] + buf[0][x+2] +
                         buf[1][x] + buf[2][x+1] + buf[1][x+2] +
@@ -3370,6 +3370,142 @@ smooth_region (PixelRegion *region)
   g_free (out);
 }
 
+/*  Erode (radius 1 pixel) a mask (1bpp).  */
+void
+erode_region (PixelRegion *region)
+{
+  gint      x, y;
+  gint      width;
+  gint      i;
+  guchar   *buf[3];
+  guchar   *out;
+
+  width = region->w;
+
+  for (i = 0; i < 3; i++)
+    buf[i] = g_new (guchar, width + 2);
+
+  out = g_new (guchar, width);
+
+  /* load top of image */
+  pixel_region_get_row (region, region->x, region->y, width, buf[0] + 1, 1);
+
+  buf[0][0]         = buf[0][1];
+  buf[0][width + 1] = buf[0][width];
+
+  memcpy (buf[1], buf[2], width + 2);
+
+  for (y = 0; y < region->h; y++)
+    {
+      if (y + 1 < region->h)
+        {
+          pixel_region_get_row (region, region->x, region->y + y + 1, width,
+                                buf[2] + 1, 1);
+
+          buf[2][0]         = buf[2][1];
+          buf[2][width + 1] = buf[2][width];
+        }
+      else
+        {
+          memcpy (buf[2], buf[1], width + 2);
+        }
+
+      for (x = 0 ; x < width; x++)
+        {
+          gint min = 255;
+
+          if (buf[0][x]   < min) min = buf[0][x];
+          if (buf[0][x+1] < min) min = buf[0][x+1];
+          if (buf[0][x+2] < min) min = buf[0][x+2];
+          if (buf[1][x]   < min) min = buf[1][x];
+          if (buf[1][x+1] < min) min = buf[1][x+1];
+          if (buf[1][x+2] < min) min = buf[1][x+2];
+          if (buf[2][x]   < min) min = buf[2][x];
+          if (buf[2][x+1] < min) min = buf[2][x+1];
+          if (buf[2][x+2] < min) min = buf[2][x+2];
+
+          out[x] = min;
+        }
+
+      pixel_region_set_row (region, region->x, region->y + y, width, out);
+
+      rotate_pointers (buf, 3);
+    }
+
+  for (i = 0; i < 3; i++)
+    g_free (buf[i]);
+
+  g_free (out);
+}
+
+/*  Dilate (radius 1 pixel) a mask (1bpp).  */
+void
+dilate_region (PixelRegion *region)
+{
+  gint      x, y;
+  gint      width;
+  gint      i;
+  guchar   *buf[3];
+  guchar   *out;
+
+  width = region->w;
+
+  for (i = 0; i < 3; i++)
+    buf[i] = g_new (guchar, width + 2);
+
+  out = g_new (guchar, width);
+
+  /* load top of image */
+  pixel_region_get_row (region, region->x, region->y, width, buf[0] + 1, 1);
+
+  buf[0][0]         = buf[0][1];
+  buf[0][width + 1] = buf[0][width];
+
+  memcpy (buf[1], buf[2], width + 2);
+
+  for (y = 0; y < region->h; y++)
+    {
+      if (y + 1 < region->h)
+        {
+          pixel_region_get_row (region, region->x, region->y + y + 1, width,
+                                buf[2] + 1, 1);
+
+          buf[2][0]         = buf[2][1];
+          buf[2][width + 1] = buf[2][width];
+        }
+      else
+        {
+          memcpy (buf[2], buf[1], width + 2);
+        }
+
+      for (x = 0 ; x < width; x++)
+        {
+          gint max = 0;
+
+          if (buf[0][x]   < max) max = buf[0][x];
+          if (buf[0][x+1] < max) max = buf[0][x+1];
+          if (buf[0][x+2] < max) max = buf[0][x+2];
+          if (buf[1][x]   < max) max = buf[1][x];
+          if (buf[1][x+1] < max) max = buf[1][x+1];
+          if (buf[1][x+2] < max) max = buf[1][x+2];
+          if (buf[2][x]   < max) max = buf[2][x];
+          if (buf[2][x+1] < max) max = buf[2][x+1];
+          if (buf[2][x+2] < max) max = buf[2][x+2];
+
+          out[x] = max;
+        }
+
+      pixel_region_set_row (region, region->x, region->y + y, width, out);
+
+      rotate_pointers (buf, 3);
+    }
+
+  for (i = 0; i < 3; i++)
+    g_free (buf[i]);
+
+  g_free (out);
+}
+
 static void
 compute_transition (guchar  *transition,
                     guchar **buf,
diff --git a/app/paint-funcs/paint-funcs.h b/app/paint-funcs/paint-funcs.h
index 9c0400e7db..665be0d380 100644
--- a/app/paint-funcs/paint-funcs.h
+++ b/app/paint-funcs/paint-funcs.h
@@ -388,6 +388,8 @@ void  fatten_region                       (PixelRegion *region,
                                            gint16       yradius);
 
 void  smooth_region                       (PixelRegion *region);
+void  erode_region                        (PixelRegion *region);
+void  dilate_region                       (PixelRegion *region);
 
 void  swap_region                         (PixelRegion *src,
                                            PixelRegion *dest);