diff --git a/otherlibs/graph/color.c b/otherlibs/graph/color.c
index 75addc608..c2f569738 100644
--- a/otherlibs/graph/color.c
+++ b/otherlibs/graph/color.c
@@ -29,6 +29,11 @@ static struct color_cache_entry color_cache[Color_cache_size];
 
 static int num_overflows = 0;
 
+Bool direct_rgb = False;
+int byte_order;
+int bitmap_unit;
+int bits_per_pixel;
+
 void gr_init_color_cache(void)
 {
   int i;
@@ -46,10 +51,22 @@ unsigned long gr_pixel_rgb(int rgb)
   unsigned int r, g, b;
   int h, i;
   XColor color;
+  unsigned short tmp;
 
   r = (rgb >> 16) & 0xFF;
   g = (rgb >> 8) & 0xFF;
   b = rgb & 0xFF;
+
+  if (direct_rgb){
+    switch ( bits_per_pixel ){
+    case 16:
+	tmp = ((r >> 3) << 11) + ((g >> 2) << 5) + ((b >> 3) << 0);
+	return (unsigned long) tmp;
+    case 32:
+      return (r << 16) + (g << 8) + (b << 0);
+    }
+  }
+
   h = Hash_rgb(r, g, b);
   i = h;
   while(1) {
@@ -57,13 +74,13 @@ unsigned long gr_pixel_rgb(int rgb)
     if (color_cache[i].rgb == rgb) return color_cache[i].pixel;
     i = (i + 1) & (Color_cache_size - 1);
     if (i == h) {
-      /* Cache is full.  Instead of inserting at slot h, which causes
-         thrasing if many colors hash to the same value,
-         insert at h + n where n is pseudo-random and
-         smaller than Color_cache_slack */
-      int slack = num_overflows++ & (Color_cache_slack - 1);
-      i = (i + slack) & (Color_cache_size - 1);
-      break;
+	/* Cache is full.  Instead of inserting at slot h, which causes
+	   thrasing if many colors hash to the same value,
+	   insert at h + n where n is pseudo-random and
+	   smaller than Color_cache_slack */
+	int slack = num_overflows++ & (Color_cache_slack - 1);
+	i = (i + slack) & (Color_cache_size - 1);
+	break;
     }
   }
   color.red = r * 0x101;
diff --git a/otherlibs/graph/libgraph.h b/otherlibs/graph/libgraph.h
index 0e58bace2..ac8a50bd5 100644
--- a/otherlibs/graph/libgraph.h
+++ b/otherlibs/graph/libgraph.h
@@ -32,6 +32,11 @@ extern int grx, gry;            /* Coordinates of the current point */
 extern unsigned long grcolor;   /* Current drawing color */
 extern XFontStruct * grfont;    /* Current font */
 
+extern Bool direct_rgb;
+extern int byte_order;
+extern int bitmap_unit;
+extern int bits_per_pixel;
+
 #define Wcvt(y) (grwindow.h - 1 - (y))
 #define Bcvt(y) (grbstore.h - 1 - (y))
 #define WtoB(y) ((y) + grbstore.h - grwindow.h)
diff --git a/otherlibs/graph/make_img.c b/otherlibs/graph/make_img.c
index 2d6bfe960..fdd601cba 100644
--- a/otherlibs/graph/make_img.c
+++ b/otherlibs/graph/make_img.c
@@ -40,6 +40,22 @@ value gr_make_image(value m)
                  XDefaultDepth(grdisplay, grscreen),
                  ZPixmap, 0, NULL, width, height,
                  BitmapPad(grdisplay), 0);
+
+  /* To optimize RGB => color id calculation */
+  if( !direct_rgb ){
+    /* they are declared in color.c */
+    byte_order = idata->byte_order;
+    bitmap_unit = idata->bitmap_unit;
+    bits_per_pixel = idata->bits_per_pixel;
+#ifdef DIRECT_RGB_DEBUG
+    fprintf(stderr, "Byte_order: %d = %s\n", byte_order,
+	    byte_order ? "LSBFirst" : "MSBFirst");
+    fprintf(stderr, "Bitmp_unit: %d\n", bitmap_unit);
+    fprintf(stderr, "Bits per pixel: %d\n", idata->bits_per_pixel);
+#endif
+    direct_rgb = True;
+  }
+
   bdata = (char *) stat_alloc(height * idata->bytes_per_line);
   idata->data = bdata;
   has_transp = False;