diff --git a/defines.h b/defines.h
index 0ba7200..6cc18aa 100644
--- a/defines.h
+++ b/defines.h
@@ -86,7 +86,7 @@
 #define ADJUST_GREY (1<<6)
 #define DEBUG_OUTPUT (1<<7)
 
-/* colours used by ssocr */
+/* colors used by ssocr */
 #define SSOCR_BLACK 0
 #define SSOCR_WHITE 255
 
diff --git a/help.c b/help.c
index 09492a0..9f9500c 100644
--- a/help.c
+++ b/help.c
@@ -98,7 +98,7 @@ void usage(char *name, FILE *f)
   fprintf(f, "         -f, --foreground=COLOR   set foreground color (black or white)\n");
   fprintf(f, "         -b, --background=COLOR   set foreground color (black or white)\n");
   fprintf(f, "         -I, --print-info         print image dimensions and used lum values\n");
-  fprintf(f, "         -g, --adjust-grey        use T1 and T2 as percentages of used values\n");
+  fprintf(f, "         -g, --adjust-gray        use T1 and T2 as percentages of used values\n");
   fprintf(f, "         -l, --luminance=KEYWORD  compute luminance using formula KEYWORD\n");
   fprintf(f, "                                  use -l help for list of KEYWORDS\n");
   fprintf(f, "\nCommands: dilation                dilation algorithm (with mask of 1 pixel)\n");
@@ -109,9 +109,9 @@ void usage(char *name, FILE *f)
   fprintf(f, "                                  ([N times] erosion then [N times] dilation)\n");
   fprintf(f, "          remove_isolated         remove isolated pixels\n");
   fprintf(f, "          make_mono               make image monochrome\n");
-  fprintf(f, "          greyscale               transform image to greyscale\n");
+  fprintf(f, "          grayscale               transform image to grayscale\n");
   fprintf(f, "          invert                  make inverted monochrome image\n");
-  fprintf(f, "          grey_stretch T1 T2      stretch luminance values\n");
+  fprintf(f, "          gray_stretch T1 T2      stretch luminance values\n");
   fprintf(f, "                                  from [T1,T2] to [0,255]\n");
   fprintf(f, "          dynamic_threshold W H   make image monochrome w. dynamic thresholding\n");
   fprintf(f, "                                  with a window of width W and height H\n");
diff --git a/imgproc.c b/imgproc.c
index fff3d7b..4d38a5c 100644
--- a/imgproc.c
+++ b/imgproc.c
@@ -307,9 +307,9 @@ Imlib_Image remove_isolated(Imlib_Image *source_image, double thresh,
   return keep_pixels_filter(source_image, thresh, lt, 1);
 }
 
-/* grey stretching, i.e. lum<t1 => lum=0, lum>t2 => lum=100,
+/* gray stretching, i.e. lum<t1 => lum=0, lum>t2 => lum=100,
  * else lum=((lum-t1)*MAXRGB)/(t2-t1) */
-Imlib_Image grey_stretch(Imlib_Image *source_image, double t1, double t2,
+Imlib_Image gray_stretch(Imlib_Image *source_image, double t1, double t2,
                          luminance_t lt)
 {
   Imlib_Image new_image; /* construct filtered image here */
@@ -321,17 +321,17 @@ Imlib_Image grey_stretch(Imlib_Image *source_image, double t1, double t2,
 
   /* do nothing if t1>=t2 */
   if(t1 >= t2) {
-    fprintf(stderr, "error: grey_stretch(): t1=%.2f >= t2=%.2f\n", t1, t2);
+    fprintf(stderr, "error: gray_stretch(): t1=%.2f >= t2=%.2f\n", t1, t2);
     exit(99);
   }
 
   /* check if 0 < t1,t2 < MAXRGB */
   if(t1 <= 0.0) {
-    fprintf(stderr, "error: grey_stretch(): t1=%.2f <= 0.0\n", t1);
+    fprintf(stderr, "error: gray_stretch(): t1=%.2f <= 0.0\n", t1);
     exit(99);
   }
   if(t2 >= MAXRGB) {
-    fprintf(stderr, "error: grey_stretch(): t2=%.2f >= %d.0\n", t2, MAXRGB);
+    fprintf(stderr, "error: gray_stretch(): t2=%.2f >= %d.0\n", t2, MAXRGB);
     exit(99);
   }
 
@@ -344,7 +344,7 @@ Imlib_Image grey_stretch(Imlib_Image *source_image, double t1, double t2,
   width = imlib_image_get_width();
   new_image = imlib_clone_image();
 
-  /* grey stretch image */
+  /* gray stretch image */
   for(x=0; x<width; x++) {
     for(y=0; y<height; y++) {
       imlib_image_query_pixel(x, y, &color);
@@ -877,10 +877,10 @@ Imlib_Image rotate(Imlib_Image *source_image, double theta)
   return new_image;
 }
 
-/* turn image to greyscale */
-Imlib_Image greyscale(Imlib_Image *source_image, luminance_t lt)
+/* turn image to grayscale */
+Imlib_Image grayscale(Imlib_Image *source_image, luminance_t lt)
 {
-  Imlib_Image new_image; /* construct greyscale image here */
+  Imlib_Image new_image; /* construct grayscale image here */
   Imlib_Image current_image; /* save image pointer */
   int height, width; /* image dimensions */
   int x,y; /* iteration variables */
@@ -896,7 +896,7 @@ Imlib_Image greyscale(Imlib_Image *source_image, luminance_t lt)
   width = imlib_image_get_width();
   new_image = imlib_clone_image();
 
-  /* transform image to greyscale */
+  /* transform image to grayscale */
   for(x=0; x<width; x++) {
     for(y=0; y<height; y++) {
       imlib_context_set_image(*source_image);
diff --git a/imgproc.h b/imgproc.h
index 904ae56..bc4f894 100644
--- a/imgproc.h
+++ b/imgproc.h
@@ -73,9 +73,9 @@ Imlib_Image keep_pixels_filter(Imlib_Image *source_image, double thresh,
 Imlib_Image remove_isolated(Imlib_Image *source_image, double thresh,
                             luminance_t lt);
 
-/* grey stretching, i.e. lum<t1 => lum=0, lum>t2 => lum=100,
+/* gray stretching, i.e. lum<t1 => lum=0, lum>t2 => lum=100,
  * else lum=((lum-t1)*MAXRGB)/(t2-t1) */
-Imlib_Image grey_stretch(Imlib_Image *source_image, double t1, double t2,
+Imlib_Image gray_stretch(Imlib_Image *source_image, double t1, double t2,
                          luminance_t lt);
 
 /* use dynamic (aka adaptive) local thresholding to create monochrome image */
@@ -114,8 +114,8 @@ Imlib_Image shear(Imlib_Image *source_image, int offset);
 /* rotate the image */
 Imlib_Image rotate(Imlib_Image *source_image, double theta);
 
-/* turn image to greyscale */
-Imlib_Image greyscale(Imlib_Image *source_image, luminance_t lt);
+/* turn image to grayscale */
+Imlib_Image grayscale(Imlib_Image *source_image, luminance_t lt);
 
 /* crop image */
 Imlib_Image crop(Imlib_Image *source_image, int x, int y, int w, int h);
@@ -133,11 +133,11 @@ double get_threshold(Imlib_Image *source_image, double fraction, luminance_t lt,
 double iterative_threshold(Imlib_Image *source_image, double thresh,
                            luminance_t lt, int x, int y, int w, int h);
 
-/* get minimum grey value */
+/* get minimum gray value */
 double get_minval(Imlib_Image *source_image, int x, int y, int w, int h,
                  luminance_t lt);
 
-/* get maximum grey value */
+/* get maximum gray value */
 double get_maxval(Imlib_Image *source_image, int x, int y, int w, int h,
                  luminance_t lt);
 
diff --git a/ssocr.1.in b/ssocr.1.in
index 57ad257..82a4dc3 100644
--- a/ssocr.1.in
+++ b/ssocr.1.in
@@ -108,13 +108,13 @@ Default is
 .IR white .
 .SS -I, --print-info
 Prints image dimensions and range of used luminance values to standard error.
-.SS -g, --adjust-grey
+.SS -g, --adjust-gray
 Interpret the values
 .B T1
 and
 .B T2
 given to the command
-.B grey_stretch
+.B gray_stretch
 as percentages instead of absolut luminance values.
 .SS -l, --luminance KEYWORD
 Choose the type of luminace computation.
@@ -167,13 +167,13 @@ The threshold can be specified with option
 and is adjusted to the used luminance interval of the image unless option
 .B --absolute-threshold
 is used.
-.SS greyscale
-Transform image to grey values using luminance.
+.SS grayscale
+Transform image to gray values using luminance.
 The formula to compute luminance can be specified using option
 .BR --luminance .
 .SS invert
 Set every foreground pixel to background color and vice versa.
-.SS grey_stretch T1 T2
+.SS gray_stretch T1 T2
 Transform image so that the luminance interval [
 .BR T1 , T2
 ] is projected to [
diff --git a/ssocr.c b/ssocr.c
index 848b3ee..12776c0 100644
--- a/ssocr.c
+++ b/ssocr.c
@@ -95,7 +95,7 @@ int main(int argc, char **argv)
       {"foreground", 1, 0, 'f'}, /* set foreground color */
       {"background", 1, 0, 'b'}, /* set background color */
       {"print-info", 0, 0, 'I'}, /* print image info */
-      {"adjust-grey", 0, 0, 'g'}, /* use T1 and T2 as perecntages of used vals*/
+      {"adjust-gray", 0, 0, 'g'}, /* use T1 and T2 as perecntages of used vals*/
       {"luminance", 1, 0, 'l'}, /* luminance formula */
       {0, 0, 0, 0} /* terminate long options */
     };
@@ -552,13 +552,13 @@ int main(int argc, char **argv)
           imlib_context_set_image(image);
           imlib_free_image();
           image = new_image;
-        } else if(strcasecmp("grey_stretch",argv[i]) == 0) {
+        } else if(strcasecmp("gray_stretch",argv[i]) == 0) {
           if(i+2<argc-1) {
             double t1, t2;
             t1 = atof(argv[i+1]);
             t2 = atof(argv[i+2]);
             if(flags & VERBOSE) {
-              fprintf(stderr, " processing grey_stretch %.2f %.2f", t1, t2);
+              fprintf(stderr, " processing gray_stretch %.2f %.2f", t1, t2);
               if(flags & DEBUG_OUTPUT) {
                 fprintf(stderr," (from strings %s and %s)",argv[i+1],argv[i+2]);
               }
@@ -578,19 +578,19 @@ int main(int argc, char **argv)
                 fprintf(stderr, " adjusted to T1=%.2f and T2=%.2f\n", t1, t2);
               }
             }
-            i+=2; /* skip the arguments to grey_stretch */
-            new_image = grey_stretch(&image, t1, t2, lt);
+            i+=2; /* skip the arguments to gray_stretch */
+            new_image = gray_stretch(&image, t1, t2, lt);
             imlib_context_set_image(image);
             imlib_free_image();
             image = new_image;
           } else {
             fprintf(stderr,
-                "error: grey_stretch command needs two arguments\n");
+                "error: gray_stretch command needs two arguments\n");
             exit(99);
           }
-        } else if(strcasecmp("greyscale",argv[i]) == 0) {
-          if(flags & VERBOSE) fputs(" processing greyscale\n", stderr);
-          new_image = greyscale(&image, lt);
+        } else if(strcasecmp("grayscale",argv[i]) == 0) {
+          if(flags & VERBOSE) fputs(" processing grayscale\n", stderr);
+          new_image = grayscale(&image, lt);
           imlib_context_set_image(image);
           imlib_free_image();
           image = new_image;
@@ -868,7 +868,7 @@ int main(int argc, char **argv)
     if(flags & USE_DEBUG_IMAGE) {
     /* draw rectangles around digits */
       imlib_context_set_image(debug_image);
-      imlib_context_set_color(128,128,128,255); /* grey line */
+      imlib_context_set_color(128,128,128,255); /* gray line */
       for(d=0; d<number_of_digits; d++) {
         imlib_image_draw_rectangle(digits[d].x1, digits[d].y1,
             digits[d].x2-digits[d].x1, digits[d].y2-digits[d].y1);