Backport PR matplotlib#31967: Fix NoNorm cursor formatting for uint8 images

Author: rcomer

lib/matplotlib/colorizer.py

@@ -505,7 +505,8 @@ def _sig_digits_from_norm(norm, data, n):
                 delta = np.abs(norm.vmin * .1)
             else:
                 # Midpoints of neighboring color intervals.
-                neighbors = norm.inverse((int(normed * n) + np.array([0, 1])) / n)
+                neighbors = norm.inverse(
+                    (int(float(normed) * n) + np.array([0, 1])) / n)
                 delta = abs(neighbors - data).max()
 
             g_sig_digits = cbook._g_sig_digits(data, delta)

lib/matplotlib/tests/test_image.py

@@ -14,6 +14,7 @@
 import matplotlib as mpl
 from matplotlib import (
     colors, image as mimage, patches, pyplot as plt, style, rcParams)
+from matplotlib.backend_bases import MouseEvent
 from matplotlib.image import (AxesImage, BboxImage, FigureImage,
                               NonUniformImage, PcolorImage)
 from matplotlib.patches import Rectangle
@@ -455,8 +456,6 @@ def test_cursor_data_nonuniform(xy, data):
         ([[0, 0]], "[0.00]"),
     ])
 def test_format_cursor_data(data, text):
-    from matplotlib.backend_bases import MouseEvent
-
     fig, ax = plt.subplots()
     im = ax.imshow(data)
 
@@ -465,14 +464,23 @@ def test_format_cursor_data(data, text):
     assert im.format_cursor_data(im.get_cursor_data(event)) == text
 
 
+def test_format_cursor_data_uint8_no_norm():
+    data = np.array([[0, 44]], dtype=np.uint8)
+    fig, ax = plt.subplots()
+    im = ax.imshow(data, norm=colors.NoNorm())
+
+    xdisp, ydisp = ax.transData.transform([1, 0])
+    event = MouseEvent('motion_notify_event', fig.canvas, xdisp, ydisp)
+    assert im.format_cursor_data(im.get_cursor_data(event)) == "[44.000]"
+
+
 @pytest.mark.parametrize(
     "data, text", [
         ([[[10001, 10000]], [[0, 0]]], "[10001.000, 0.000]"),
         ([[[.123, .987]], [[0.1, 0]]], "[0.123, 0.100]"),
         ([[[np.nan, 1, 2]], [[0, 0, 0]]], "[]"),
     ])
 def test_format_cursor_data_multinorm(data, text):
-    from matplotlib.backend_bases import MouseEvent
     fig, ax = plt.subplots()
     cmap_bivar = mpl.bivar_colormaps['BiOrangeBlue']
     cmap_multivar = mpl.multivar_colormaps['2VarAddA']