Fixes colors normalization with 'under' colors in LinearSegmentedColormap (values between -1 and 0 were being made positive due to an int cast).

WeatherGod · WeatherGod · commit bfe603229250 · 2011-01-21T21:42:45.000Z
Thanks to Eoghan Harrington for discovering and supplying the patch!

svn path=/branches/v1_0_maint/; revision=8931
diff --git a/lib/matplotlib/colors.py b/lib/matplotlib/colors.py
@@ -523,6 +523,10 @@ def __call__(self, X, alpha=None, bytes=False):
                 np.clip(xa * self.N, -1, self.N, out=xa)
             else:
                 xa = np.clip(xa * self.N, -1, self.N)
+
+            # ensure that all 'under' values will still have negative
+            # value after casting to int
+            np.putmask(xa, xa<0.0, -1)
             xa = xa.astype(int)
         # Set the over-range indices before the under-range;
         # otherwise the under-range values get converted to over-range.
