diff --git a/dither_apply.pyx b/dither_apply.pyx
index 8b06801..38da652 100644
--- a/dither_apply.pyx
+++ b/dither_apply.pyx
@@ -50,6 +50,27 @@ cdef x_dither_bounds(float [:, :, ::1] pattern, int x_origin, int x_res, int x):
     return el, er, xl, xr
 
 
+cdef long* flatten_rgb(float [:, :, ::1] rgb):
+    cdef i, j, k
+    cdef long *flat = <long *> malloc(rgb.shape[0] * rgb.shape[1] * sizeof(long))
+    for i in range(rgb.shape[0]):
+        for j in range(rgb.shape[1]):
+            for k in range(rgb.shape[2]):
+                flat[i * rgb.shape[1] + j] = (int(rgb[i, j, 0]) << 16) + (int(rgb[i, j, 1]) << 8) + (int(rgb[i, j, 2]))
+    return flat
+
+
+cdef char* distance(char [:, ::1] distances, float [:, :, ::1] rgb, char [:, ::1] bit4):
+    flat = flatten_rgb(rgb)
+
+    cdef char *dist = <char *> malloc(rgb.shape[0] * rgb.shape[1] * sizeof(char))
+    for i in range(rgb.shape[0]):
+        for j in range(rgb.shape[1]):
+            dist[i * rgb.shape[1] + j] = distances[flat[i * rgb.shape[1] + j], bit4[i, j]]
+    free(flat)
+    return dist
+
+
 def dither_lookahead(
         screen, float[:,:,::1] image_rgb, dither, differ, int x, int y, char[:, ::1] options_4bit,
         float[:, :, ::1] options_rgb, int lookahead):
@@ -63,11 +84,10 @@ def dither_lookahead(
     # X coord value of larger of dither bounding box or lookahead horizon
     cdef int xxr = min(max(x + lookahead, xr), x_res)
 
-    # copies of input pixels so we can dither in bulk
-    # Leave enough space so we can dither the last of our lookahead pixels
+    # Copies of input pixels so we can dither in bulk
+    # Leave enough space at right of image so we can dither the last of our lookahead pixels
     cdef float[:, :, ::1] lah_image_rgb = np.zeros(
         (2 ** lookahead, lookahead + xr - xl, 3), dtype=np.float32)
-    # XXX opt
     lah_image_rgb[:, 0:xxr - x, :] = image_rgb[y, x:xxr, :]
 
     cdef float[:, ::] output_pixels
@@ -92,8 +112,30 @@ def dither_lookahead(
 
     free(quant_error)
 
-    # XXX opt
-    cdef long[:, ::1] error = differ.distance(np.clip(lah_image_rgb[:, 0:lookahead, :], 0, 255), options_4bit)
-    cdef long[::1] total_error = np.sum(np.power(error, 2), axis=1)
-    cdef int best = np.argmin(total_error)
+    # Clip lah_image_rgb into 0..255 range to prepare for computing colour distance
+    #for i in range(2**lookahead):
+    #    for j in range(lookahead):
+    #        for k in range(3):
+    #            lah_image_rgb[i, j, k] = clip(lah_image_rgb[i, j, k], 0, 255)
+
+    # cdef char* error = distance(differ._distances, lah_image_rgb[:, 0:lookahead, :], options_4bit)
+    # differ.distance(lah_image_rgb[:, 0:lookahead, :], options_4bit)
+    cdef long[:, ::1] error = differ.distance(lah_image_rgb[:, 0:lookahead, :], options_4bit)
+    cdef int best
+    cdef int best_error = 2**31-1
+    cdef int total_error
+    for i in range(2**lookahead):
+        total_error = 0
+        for j in range(lookahead):
+            total_error += error[i, j] ** 2
+            if total_error >= best_error:
+                break
+        if total_error < best_error:
+            best_error = total_error
+            best = i
+
+    #cdef long[::1] total_error = np.sum(np.power(error, 2), axis=1)
+    #cdef int best = np.argmin(total_error)
+
+    # free(error)
     return options_4bit[best, 0], options_rgb[best, 0, :]
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