diff --git a/convert.py b/convert.py
index e532a92..a90c7e6 100644
--- a/convert.py
+++ b/convert.py
@@ -102,32 +102,43 @@ class ClusterPalette:
                                    int(np.round(palette_upper))))
         return palette_ranges
 
+    def _dither_image(self, palettes_cam, penalty):
+        # Suppress divide by zero warning,
+        # https://github.com/colour-science/colour/issues/900
+        with colour.utilities.suppress_warnings(python_warnings=True):
+            palettes_linear_rgb = colour.convert(
+                palettes_cam, "CAM16UCS", "RGB").astype(np.float32)
+
+        output_4bit, line_to_palette, total_image_error = \
+            dither_pyx.dither_shr(
+                self._image_rgb, palettes_cam, palettes_linear_rgb,
+                self._rgb24_to_cam16ucs, float(penalty))
+
+        return (output_4bit, line_to_palette, palettes_linear_rgb,
+                total_image_error)
+
     def iterate(self, penalty: float, max_iterations: int):
         iterations_since_improvement = 0
         total_image_error = 1e9
 
         last_good_splits = self._palette_splits
+        (output_4bit, line_to_palette, palettes_linear_rgb,
+         new_total_image_error) = self._dither_image(
+            self._palettes_cam, penalty)
 
         while iterations_since_improvement < max_iterations:
+            self._reassign_unused_palettes(line_to_palette,
+                                           last_good_splits)
+
             # print("Iterations %d" % iterations_since_improvement)
             new_palettes_cam, new_palettes_rgb12_iigs, new_palette_errors = (
                 self._propose_palettes())
 
-            # Suppress divide by zero warning,
-            # https://github.com/colour-science/colour/issues/900
-            with colour.utilities.suppress_warnings(python_warnings=True):
-                new_palettes_linear_rgb = colour.convert(
-                    new_palettes_cam, "CAM16UCS", "RGB").astype(np.float32)
-
             # Recompute image with proposed palettes and check whether it has
             # lower total image error than our previous best.
-            new_output_4bit, new_line_to_palette, new_total_image_error = \
-                dither_pyx.dither_shr(
-                    self._image_rgb, new_palettes_cam, new_palettes_linear_rgb,
-                    self._rgb24_to_cam16ucs, float(penalty))
-
-            self._reassign_unused_palettes(new_line_to_palette,
-                                           last_good_splits)
+            (output_4bit, line_to_palette, palettes_linear_rgb,
+             new_total_image_error) = self._dither_image(
+                new_palettes_cam, penalty)
 
             if new_total_image_error >= total_image_error:
                 iterations_since_improvement += 1
@@ -143,8 +154,8 @@ class ClusterPalette:
             self._errors = new_palette_errors
             self._palettes_accepted = True
 
-            yield (new_total_image_error, new_output_4bit, new_line_to_palette,
-                   new_palettes_rgb12_iigs, new_palettes_linear_rgb)
+            yield (new_total_image_error, output_4bit, line_to_palette,
+                   new_palettes_rgb12_iigs, palettes_linear_rgb)
 
     def _propose_palettes(self) -> Tuple[np.ndarray, np.ndarray, List[float]]:
         """Attempt to find new palettes that locally improve image quality.