diff --git a/simgear/screen/texture.cxx b/simgear/screen/texture.cxx
index 91550edb..f306bc76 100644
--- a/simgear/screen/texture.cxx
+++ b/simgear/screen/texture.cxx
@@ -795,7 +795,7 @@ SGTexture::ConvertUint(unsigned *array, unsigned int length) {
 
 
 void
-SGTexture::make_monochrome(GLubyte r, GLubyte g, GLubyte b) {
+SGTexture::make_monochrome(float contrast, GLubyte r, GLubyte g, GLubyte b) {
 
    if (num_colors >= 3)
       return;
@@ -815,8 +815,32 @@ SGTexture::make_monochrome(GLubyte r, GLubyte g, GLubyte b) {
       }
 }
 
+
 void
-SGTexture::make_normalmap(float brightness) {
+SGTexture::make_grayscale(float contrast) {
+   if (num_colors >= 3)
+      return;
+
+   GLubyte *map = (GLubyte *)malloc (texture_width * texture_height);
+   for (int y=0; y<texture_height; y++)
+      for (int x=0; x<texture_width; x++)
+      {
+         GLubyte *rgb = get_pixel(x,y);
+         GLubyte avg = (rgb[0] + rgb[1] + rgb[2]) / 3;
+
+         map[x +y*texture_height] = avg;
+      }
+
+   free (texture_data);
+   texture_data = map;
+   num_colors = 1;
+}
+
+
+void
+SGTexture::make_normalmap(float brightness, float contrast) {
+   make_grayscale(contrast);
+
    GLubyte *map = (GLubyte *)malloc (texture_width * texture_height * 3);
 
    for (int y=0; y<texture_height; y++)
diff --git a/simgear/screen/texture.hxx b/simgear/screen/texture.hxx
index 9f5f48bd..bfcb0781 100644
--- a/simgear/screen/texture.hxx
+++ b/simgear/screen/texture.hxx
@@ -140,8 +140,10 @@ public:
     inline const char *err_str() { return errstr; }
     inline void clear_err_str() { errstr = ""; }
 
-    void make_monochrome(GLubyte r=255, GLubyte g=255, GLubyte b=255);
-    void make_normalmap(float brightness = 1.0);
+    void make_grayscale(float contrast = 1.0);
+    void make_monochrome(float contrast = 1.0,
+                         GLubyte r=255, GLubyte g=255, GLubyte b=255);
+    void make_normalmap(float brightness = 1.0, float contrast = 1.0);
 };
 
 #endif