BUG: fix ListedColormap._resample, hence plt.get_cmap; closes #6025

matplotlib · tacaswell · Feb 21, 2016 · Feb 20, 2016 · Feb 20, 2016 · 8d2da2c06273cdb17dd9ba53b47387bfbfd43fdf
commit 8d2da2c06273cdb17dd9ba53b47387bfbfd43fdf
diff --git a/lib/matplotlib/colors.py b/lib/matplotlib/colors.py
@@ -852,7 +852,8 @@ def _resample(self, lutsize):
        """
        Return a new color map with *lutsize* entries.
        """
-        return ListedColormap(self.name, self.colors, lutsize)
+        colors = self(np.linspace(0, 1, lutsize))
+        return ListedColormap(colors, name=self.name)


 class Normalize(object):

diff --git a/lib/matplotlib/tests/test_colors.py b/lib/matplotlib/tests/test_colors.py
@@ -18,6 +18,28 @@
                                           cleanup, knownfailureif)


+def test_resample():
+    """
+    Github issue #6025 pointed to incorrect ListedColormap._resample;
+    here we test the method for LinearSegmentedColormap as well.
+    """
+    n = 101
+    colorlist = np.empty((n, 4), float)
+    colorlist[:, 0] = np.linspace(0, 1, n)
+    colorlist[:, 1] = 0.2
+    colorlist[:, 2] = np.linspace(1, 0, n)
+    colorlist[:, 3] = 0.7
+    lsc = mcolors.LinearSegmentedColormap.from_list('lsc', colorlist)
+    lc = mcolors.ListedColormap(colorlist)
+    lsc3 = lsc._resample(3)
+    lc3 = lc._resample(3)
+    expected = np.array([[0.0, 0.2, 1.0, 0.7],
+                         [0.5, 0.2, 0.5, 0.7],
+                         [1.0, 0.2, 0.0, 0.7]], float)
+    assert_array_almost_equal(lsc3([0, 0.5, 1]), expected)
+    assert_array_almost_equal(lc3([0, 0.5, 1]), expected)
+
+
 def test_colormap_endian():
    """
    Github issue #1005: a bug in putmask caused erroneous