Merge pull request matplotlib#25498 from greglucas/cbar-new-norm

FIX: Use mappable data when autoscaling colorbar norm

Author: jklymak

lib/matplotlib/colorbar.py

@@ -301,11 +301,6 @@ def __init__(self, ax, mappable=None, *, cmap=None,
         if mappable is None:
             mappable = cm.ScalarMappable(norm=norm, cmap=cmap)
 
-        # Ensure the given mappable's norm has appropriate vmin and vmax
-        # set even if mappable.draw has not yet been called.
-        if mappable.get_array() is not None:
-            mappable.autoscale_None()
-
         self.mappable = mappable
         cmap = mappable.cmap
         norm = mappable.norm
@@ -1091,7 +1086,10 @@ def _process_values(self):
             b = np.hstack((b, b[-1] + 1))
 
         # transform from 0-1 to vmin-vmax:
+        if self.mappable.get_array() is not None:
+            self.mappable.autoscale_None()
         if not self.norm.scaled():
+            # If we still aren't scaled after autoscaling, use 0, 1 as default
             self.norm.vmin = 0
             self.norm.vmax = 1
         self.norm.vmin, self.norm.vmax = mtransforms.nonsingular(

lib/matplotlib/tests/test_colorbar.py

@@ -653,6 +653,12 @@ def test_colorbar_scale_reset():
 
     assert cbar.outline.get_edgecolor() == mcolors.to_rgba('red')
 
+    # log scale with no vmin/vmax set should scale to the data if there
+    # is a mappable already associated with the colorbar, not (0, 1)
+    pcm.norm = LogNorm()
+    assert pcm.norm.vmin == z.min()
+    assert pcm.norm.vmax == z.max()
+
 
 def test_colorbar_get_ticks_2():
     plt.rcParams['_internal.classic_mode'] = False