Use check_figures_equal.

tillahoffmann · tillahoffmann · commit fc64a19e99b1 · 2019-09-04T14:36:02.000+01:00
diff --git a/lib/matplotlib/image.py b/lib/matplotlib/image.py
@@ -293,7 +293,8 @@ def set_alpha(self, alpha):
         self._imcache = None
 
     def _get_scalar_alpha(self):
-        return self._alpha if np.ndim(self._alpha) == 0 else 1.0
+        return 1.0 if self._alpha is None or np.ndim(self._alpha) > 0 \
+            else self._alpha
 
     def changed(self):
         """
diff --git a/lib/matplotlib/tests/test_image.py b/lib/matplotlib/tests/test_image.py
@@ -1118,3 +1118,22 @@ def test_image_cursor_formatting():
 
     data = np.nan
     assert im.format_cursor_data(data) == '[nan]'
+
+
+@check_figures_equal()
+def test_image_array_alpha(fig_test, fig_ref):
+    '''per-pixel alpha channel test'''
+    x = np.linspace(0, 1)
+    xx, yy = np.meshgrid(x, x)
+
+    zz = np.exp(- 3 * ((xx - 0.5) ** 2) + (yy - 0.7 ** 2))
+    alpha = zz / zz.max()
+
+    cmap = plt.get_cmap('viridis')
+    ax = fig_test.add_subplot(111)
+    ax.imshow(zz, alpha=alpha, cmap=cmap, interpolation='nearest')
+
+    ax = fig_ref.add_subplot(111)
+    rgba = cmap(colors.Normalize()(zz))
+    rgba[..., -1] = alpha
+    ax.imshow(rgba, interpolation='nearest')
