trygvrad · Nov 13, 2026
diff --git a/lib/matplotlib/colorbar.py b/lib/matplotlib/colorbar.py
@@ -1067,6 +1067,8 @@ def remove(self):
 
         try:
             ax = self.mappable.axes
+            if ax is None:
+                return
         except AttributeError:
             return
         try:

diff --git a/lib/matplotlib/colorizer.py b/lib/matplotlib/colorizer.py
@@ -805,7 +805,8 @@ def _ensure_norm(norm, n_components=1):
             _api.check_isinstance((colors.MultiNorm, None, tuple), norm=norm)
         if norm is None:
             norm = colors.MultiNorm(['linear']*n_components)
-        else:  # iterable, i.e. multiple strings or Normalize objects
+        elif not isinstance(norm, colors.MultiNorm):
+            # iterable, i.e. multiple strings or Normalize objects
             norm = colors.MultiNorm(norm)
         if isinstance(norm, colors.MultiNorm) and norm.n_components == n_components:
             return norm

diff --git a/lib/matplotlib/colors.py b/lib/matplotlib/colors.py
@@ -3575,11 +3575,16 @@ def autoscale_None(self, A):
             - If structured array, must have `n_components` fields. Each field
               is used for the limits of one constituent norm.
         """
+        changed = False
         with self.callbacks.blocked():
             A = self._iterable_components_in_data(A, self.n_components)
             for n, a in zip(self.norms, A):
+                vmin, vmax = n.vmin, n.vmax
                 n.autoscale_None(a)
-        self._changed()
+                if vmin != n.vmin or vmax != n.vmax:
+                    changed = True
+        if changed:
+            self._changed()
 
     def scaled(self):
         """Return whether both *vmin* and *vmax* are set on all constituent norms."""

diff --git a/lib/matplotlib/tests/test_colorbar.py b/lib/matplotlib/tests/test_colorbar.py
@@ -1254,3 +1254,18 @@ def test_colorbar_format_string_and_old():
     plt.imshow([[0, 1]])
     cb = plt.colorbar(format="{x}%")
     assert isinstance(cb._formatter, StrMethodFormatter)
+
+
+def test_remove_colorbar_with_no_mappable():
+    fig, ax = plt.subplots()
+    cb = mpl.colorbar.Colorbar(ax)
+    cb.remove()
+
+
+def test_cbar_wrong_figures():
+    fig0, ax0 = plt.subplots()
+    fig1, ax1 = plt.subplots()
+    im0 = ax0.imshow([[0, 1], [2, 3]])
+    im1 = ax1.imshow([[0, 1], [2, 3]])
+    with pytest.raises(ValueError, match="not all parents share"):
+        fig0.colorbar(im0, ax=[im0, im1])
diff --git a/lib/matplotlib/tests/test_colors.py b/lib/matplotlib/tests/test_colors.py
@@ -2225,6 +2225,25 @@ def test_colorizer_multinorm_explicit():
     assert_array_almost_equal(ca.to_rgba(data), res)
 
 
+def test_colorizer_multinorm_instance():
+    # An existing MultiNorm is used as is, not wrapped in a new MultiNorm.
+    norm = mcolors.MultiNorm(['linear', 'log'])
+    ca = mcolorizer.Colorizer('BiOrangeBlue', norm)
+    assert ca.norm is norm
+
+
+def test_multi_norm_autoscale_none_only_signals_change():
+    norm = mcolors.MultiNorm(['linear', 'linear'])
+    calls = []
+    norm.callbacks.connect('changed', lambda: calls.append(True))
+    data = [[0, 1, 2], [3, 4, 5]]
+    norm.autoscale_None(data)
+    assert len(calls) == 1
+    # limits are already set, so nothing changes and no signal is emitted
+    norm.autoscale_None(data)
+    assert len(calls) == 1
+
+
 def test_get_set_clim_raises():
     fig, ax = plt.subplots(1, 1)
     x_0 = np.arange(9, dtype='float32').reshape(3, 3)
-Original file line number
+Diff line change
@@ Expand Up / @@ -1067,6 +1067,8 @@ def remove(self): @@
             try:
                 ax = self.mappable.axes
+                if ax is None:
+                    return
             except AttributeError:
                 return
             try:
@@ Expand Down @@