diff --git a/pipi/analysis/measure.c b/pipi/analysis/measure.c
index 545f838..291f0dd 100644
--- a/pipi/analysis/measure.c
+++ b/pipi/analysis/measure.c
@@ -33,7 +33,7 @@ double pipi_measure_msd(pipi_image_t *i1, pipi_image_t *i2)
     pipi_format_t f1, f2;
     double ret = 0.0;
     float *p1, *p2;
-    int x, y, w, h;
+    int x, y, w, h, gray;
 
     w = i1->w < i2->w ? i1->w : i2->w;
     h = i1->h < i2->h ? i1->h : i2->h;
@@ -41,20 +41,54 @@ double pipi_measure_msd(pipi_image_t *i1, pipi_image_t *i2)
     f1 = i1->last_modified;
     f2 = i2->last_modified;
 
+    gray = f1 == PIPI_PIXELS_Y_F32 && f2 == PIPI_PIXELS_Y_F32;
+
     /* FIXME: this is not right */
-    pipi_get_pixels(i1, PIPI_PIXELS_Y_F32);
-    pipi_get_pixels(i2, PIPI_PIXELS_Y_F32);
-
-    p1 = (float *)i1->p[PIPI_PIXELS_Y_F32].pixels;
-    p2 = (float *)i2->p[PIPI_PIXELS_Y_F32].pixels;
-
-    for(y = 0; y < h; y++)
-        for(x = 0; x < w; x++)
-        {
-            float a = p1[y * i1->w + x];
-            float b = p2[y * i2->w + x];
-            ret += (a - b) * (a - b);
-        }
+    if(gray)
+    {
+        p1 = (float *)i1->p[PIPI_PIXELS_Y_F32].pixels;
+        p2 = (float *)i2->p[PIPI_PIXELS_Y_F32].pixels;
+    }
+    else
+    {
+        pipi_get_pixels(i1, PIPI_PIXELS_RGBA_F32);
+        pipi_get_pixels(i2, PIPI_PIXELS_RGBA_F32);
+        p1 = (float *)i1->p[PIPI_PIXELS_RGBA_F32].pixels;
+        p2 = (float *)i2->p[PIPI_PIXELS_RGBA_F32].pixels;
+    }
+
+    if(gray)
+    {
+        for(y = 0; y < h; y++)
+            for(x = 0; x < w; x++)
+            {
+                float a = p1[y * i1->w + x];
+                float b = p2[y * i2->w + x];
+                ret += (a - b) * (a - b);
+            }
+    }
+    else
+    {
+        for(y = 0; y < h; y++)
+            for(x = 0; x < w; x++)
+            {
+                float a, b, sum = 0.0;
+
+                a = p1[(y * i1->w + x) * 4];
+                b = p2[(y * i2->w + x) * 4];
+                sum += (a - b) * (a - b);
+
+                a = p1[(y * i1->w + x) * 4 + 1];
+                b = p2[(y * i2->w + x) * 4 + 1];
+                sum += (a - b) * (a - b);
+
+                a = p1[(y * i1->w + x) * 4 + 2];
+                b = p2[(y * i2->w + x) * 4 + 2];
+                sum += (a - b) * (a - b);
+
+                ret += sum / 3;
+            }
+    }
 
     /* TODO: free pixels if they were allocated */