diff --git a/defines.h b/defines.h
index 6fc5475..2350a4a 100644
--- a/defines.h
+++ b/defines.h
@@ -21,7 +21,7 @@
 #define SSOCR2_DEFINES_H
 
 /* version number */
-#define VERSION "2.17.0"
+#define VERSION "2.18.0"
 
 /* states */
 #define FIND_DARK 0
diff --git a/help.c b/help.c
index 6b584b6..58385a3 100644
--- a/help.c
+++ b/help.c
@@ -105,8 +105,12 @@ void usage(char *name, FILE *f)
   fprintf(f, "                                  use -l help for list of KEYWORDS\n");
   fprintf(f, "         -S, --ascii-art-segments print recognized segments a ASCII art\n");
   fprintf(f, "         -X, --print-as-hex       change output format to hexadecimal\n");
-  fprintf(f, "\nCommands: dilation                dilation algorithm (with mask of 1 pixel)\n");
-  fprintf(f, "          erosion                 erosion algorithm (with mask of 9 pixels)\n");
+  fprintf(f, "\nCommands: dilation [N]            [N times] dilation algorithm"
+             "\n                                  (set_pixels_filter with mask"
+	     " of 1 pixel)\n");
+  fprintf(f, "          erosion [N]             [N times] erosion algorithm\n"
+             "                                  (set_pixels_filter with mask"
+	     " of 9 pixels)\n");
   fprintf(f, "          closing [N]             closing algorithm\n");
   fprintf(f, "                                  ([N times] dilation then [N times] erosion)\n");
   fprintf(f, "          opening [N]             opening algorithm\n");
diff --git a/imgproc.c b/imgproc.c
index 74ca35e..69f3887 100644
--- a/imgproc.c
+++ b/imgproc.c
@@ -179,32 +179,15 @@ Imlib_Image set_pixels_filter(Imlib_Image *source_image, double thresh,
   return new_image;
 }
 
-Imlib_Image dilation(Imlib_Image *source_image, double thresh, luminance_t lt)
-{
-  return set_pixels_filter(source_image, thresh, lt, 1);
-}
-
-Imlib_Image erosion(Imlib_Image *source_image, double thresh, luminance_t lt)
-{
-  return set_pixels_filter(source_image, thresh, lt, 9);
-}
-
-Imlib_Image closing(Imlib_Image *source_image,double thresh,luminance_t lt,int n)
+Imlib_Image set_pixels_filter_iter(Imlib_Image *source_image, double thresh,
+                                   luminance_t lt, int mask, int iter)
 {
   int i;
   Imlib_Image temp_image1, temp_image2;
-  /* dilation n times */
   imlib_context_set_image(*source_image);
   temp_image1 = temp_image2 = imlib_clone_image();
-  for(i=0; i<n; i++) {
-    temp_image2 = dilation(&temp_image1, thresh, lt);
-    imlib_context_set_image(temp_image1);
-    imlib_free_image();
-    temp_image1 = temp_image2;
-  }
-  /* erosion n times */
-  for(i=0; i<n; i++) {
-    temp_image2 = erosion(&temp_image1, thresh, lt);
+  for(i=0; i<iter; i++) {
+    temp_image2 = set_pixels_filter(&temp_image1, thresh, lt, mask);
     imlib_context_set_image(temp_image1);
     imlib_free_image();
     temp_image1 = temp_image2;
@@ -212,27 +195,42 @@ Imlib_Image closing(Imlib_Image *source_image,double thresh,luminance_t lt,int n
   return temp_image2;
 }
 
-Imlib_Image opening(Imlib_Image *source_image,double thresh,luminance_t lt,int n)
+Imlib_Image dilation(Imlib_Image *source_image, double thresh, luminance_t lt,
+                     int n)
 {
-  int i;
-  Imlib_Image temp_image1, temp_image2;
-  /* erosion n times */
-  imlib_context_set_image(*source_image);
-  temp_image1 = temp_image2 = imlib_clone_image();
-  for(i=0; i<n; i++) {
-    temp_image2 = erosion(&temp_image1, thresh, lt);
-    imlib_context_set_image(temp_image1);
-    imlib_free_image();
-    temp_image1 = temp_image2;
-  }
+  return set_pixels_filter_iter(source_image, thresh, lt, 1, n);
+}
+
+Imlib_Image erosion(Imlib_Image *source_image, double thresh, luminance_t lt,
+                    int n)
+{
+  return set_pixels_filter_iter(source_image, thresh, lt, 9, n);
+}
+
+Imlib_Image closing(Imlib_Image *source_image, double thresh, luminance_t lt,
+                    int n)
+{
+  Imlib_Image temp_image, return_image;
   /* dilation n times */
-  for(i=0; i<n; i++) {
-    temp_image2 = dilation(&temp_image1, thresh, lt);
-    imlib_context_set_image(temp_image1);
-    imlib_free_image();
-    temp_image1 = temp_image2;
-  }
-  return temp_image2;
+  temp_image = dilation(source_image, thresh, lt, n);
+  /* erosion n times */
+  return_image = erosion(&temp_image, thresh, lt, n);
+  imlib_context_set_image(temp_image);
+  imlib_free_image();
+  return return_image;
+}
+
+Imlib_Image opening(Imlib_Image *source_image, double thresh, luminance_t lt,
+                    int n)
+{
+  Imlib_Image temp_image, return_image;
+  /* erosion n times */
+  temp_image = erosion(source_image, thresh, lt, n);
+  /* dilation n times */
+  return_image = dilation(&temp_image, thresh, lt, n);
+  imlib_context_set_image(temp_image);
+  imlib_free_image();
+  return return_image;
 }
 
 /* set pixels with (brightness) value lower than threshold that have more than
diff --git a/imgproc.h b/imgproc.h
index 51874b4..d3c02b3 100644
--- a/imgproc.h
+++ b/imgproc.h
@@ -51,11 +51,17 @@ int is_pixel_set(int value, double threshold);
 Imlib_Image set_pixels_filter(Imlib_Image *source_image, double thresh,
                               luminance_t lt, int mask);
 
+/* perform set pixel filter operation iter times */
+Imlib_Image set_pixels_filter_iter(Imlib_Image *source_image, double thresh,
+                                   luminance_t lt, int mask, int iter);
+
 /* shortcut for dilation */
-Imlib_Image dilation(Imlib_Image *source_image, double thresh, luminance_t lt);
+Imlib_Image dilation(Imlib_Image *source_image, double thresh, luminance_t lt,
+                     int n);
 
 /* shortcut for erosion */
-Imlib_Image erosion(Imlib_Image *source_image, double thresh, luminance_t lt);
+Imlib_Image erosion(Imlib_Image *source_image, double thresh, luminance_t lt,
+                    int n);
 
 /* shortcut for closing */
 Imlib_Image closing(Imlib_Image *source_image, double thresh, luminance_t lt,
diff --git a/ssocr.1.in b/ssocr.1.in
index f44790d..98ff2f2 100644
--- a/ssocr.1.in
+++ b/ssocr.1.in
@@ -170,14 +170,28 @@ Each hexadecimal number printed is the logical
 .I or
 of the set segments.
 .SH COMMANDS
-.SS dilation
+.SS dilation [N]
 Filter image using dilation algorithm.
 Any pixel with at least one neighbour pixel set in the source image will be
 set in the filtered image.
-.SS erosion
+If a number
+.B N
+>
+.I 1
+is specified, the dilation algorithm is executed
+.B N
+times.
+.SS erosion [N]
 Filter image using erosion algorithm.
 Any pixel with every neighbour pixel set in the source image will be set
 in the filtered image.
+If a number
+.B N
+>
+.I 1
+is specified, the erosion algorithm is executed
+.B N
+times.
 .SS closing [N]
 Filter image using closing algorithm, i.e. erosion and then dilation.
 If a number
diff --git a/ssocr.c b/ssocr.c
index 0d12e69..5f79cc0 100644
--- a/ssocr.c
+++ b/ssocr.c
@@ -463,14 +463,40 @@ int main(int argc, char **argv)
   if(optind < argc-1) /* then process commands */ {
     for(i=optind; i<argc-1; i++) {
       if(strcasecmp("dilation",argv[i]) == 0) {
-        if(flags & VERBOSE) fputs(" processing dilation\n", stderr);
-        new_image = dilation(&image, thresh, lt);
+        int n=atoi(argv[i+1]);
+        if((n>0) && (i+1<argc-1)) {
+          if(flags & VERBOSE) {
+            fprintf(stderr, " processing dilation %d", n);
+            if(flags & DEBUG_OUTPUT) {
+              fprintf(stderr, " (from string %s)", argv[i+1]);
+            }
+            fprintf(stderr, "\n");
+          }
+          i++;
+          new_image = dilation(&image, thresh, lt, n);
+        } else {
+          if(flags & VERBOSE) fputs(" processing dilation (1)\n", stderr);
+	  new_image = dilation(&image, thresh, lt, 1);
+	}
         imlib_context_set_image(image);
         imlib_free_image();
         image = new_image;
       } else if(strcasecmp("erosion",argv[i]) == 0) {
-        if(flags & VERBOSE) fputs(" processing erosion\n", stderr);
-        new_image = erosion(&image, thresh, lt);
+        int n=atoi(argv[i+1]);
+        if((n>0) && (i+1<argc-1)) {
+          if(flags & VERBOSE) {
+            fprintf(stderr, " processing erosion %d", n);
+            if(flags & DEBUG_OUTPUT) {
+              fprintf(stderr, " (from string %s)", argv[i+1]);
+            }
+            fprintf(stderr, "\n");
+          }
+          i++;
+          new_image = erosion(&image, thresh, lt, n);
+        } else {
+          if(flags & VERBOSE) fputs(" processing erosion (1)\n", stderr);
+	  new_image = erosion(&image, thresh, lt, 1);
+        }
         imlib_context_set_image(image);
         imlib_free_image();
         image = new_image;