Make clipping work properly for effectively planar surfaces

joferkington · joferkington · commit 3c9cacf5c16f · 2014-07-25T17:56:10.000-05:00
diff --git a/lib/matplotlib/colors.py b/lib/matplotlib/colors.py
@@ -1556,20 +1556,21 @@ def hillshade(self, elevation, vert_exag=1, dx=1, dy=1, fraction=1.):
                      + np.cos(alt) * np.cos(slope)
                      * np.cos(az - aspect))
 
-        # Apply contrast stretch
+        #-- Apply contrast stretch
         imin, imax = intensity.min(), intensity.max()
         intensity *= fraction
-        if np.abs(fraction) > 1:
-            np.clip(intensity, imin, imax, intensity)
 
-        # Rescale to 0-1, keeping range before contrast stretch
-        if imax > imin:
+        #-- Rescale to 0-1, keeping range before contrast stretch
+        # If constant slope, keep relative scaling (i.e. flat should be 0.5,
+        # fully occluded 0, etc.)
+        if (imax - imin) > 1e-6:
+            # Strictly speaking, this is incorrect. Negative values should be
+            # clipped to 0 because they're fully occluded. However, rescaling
+            # in this manner is consistent with the previous implementation and
+            # visually appears better than a "hard" clip.
             intensity -= imin
             intensity /= (imax - imin)
-        else:
-            # If constant slope, keep relative scaling
-            # (i.e. flat should be 0.5, fully occluded 0, etc.)
-            intensity = (intensity + 1) / 2
+        intensity = np.clip(intensity, 0, 1, intensity)
 
         return intensity
 
