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fix for issue #5201, empty extension triangle for vmin < 1.0 #5319

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fix for issue #5201, empty extension triangle for vmin < 1.0 #5319

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e1a8687
fix for issue #5201, empty extension triangle for vmin < 1.0
arjenve Oct 26, 2015
ba5123c
fix for issue #5201, empty extension triangle for vmin < 1.0
arjenve Oct 26, 2015
345dad1
fix for issue #5201, added test case
arjenve Oct 26, 2015
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4 changes: 2 additions & 2 deletions lib/matplotlib/colorbar.py
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Original file line number Diff line number Diff line change
Expand Up @@ -674,9 +674,9 @@ def _process_values(self, b=None):

b = self.norm.inverse(self._uniform_y(self.cmap.N + 1))
if self._extend_lower():
b[0] = b[0] - 1
b[0] = 0.9 * b[0]
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I haven't completely thought this through, but it looks to me like using a multiplier is fine for the specific case where the problem arose--a log norm--but not for the case of a linear norm. If b[0] or b[1] is zero, the multiplier doesn't do anything at all.
It also looks like the extend logic here might not even be needed, given the extend logic in _uniform_y(). I haven't checked to see how much of that was added when the ends were modified to be of variable length.
The point of all this is just to find extended b values that will be normed to less than 0 if "under" or more than 1 if "over".

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Maybe the nicest way to handle this would be to have the norm itself define two special values, one such that its norm is less than zero, and the other such that its norm is greater than one. Then the colorbar code here could just plug in those values as needed.

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It seems changing the end values is not needed for LogNorm the plot will look fine without the multiplier. The only 2 other Norm objects that reach this code are: SymLogNorm and PowerNorm. SymLogNorm cannot be inverted, so it won't work in a colorbar like this. PowerNorm has a different problem at the lower end point, I'll look into it some more...

if self._extend_upper():
b[-1] = b[-1] + 1
b[-1] = 1.1 * b[-1]
self._process_values(b)

def _find_range(self):
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13 changes: 12 additions & 1 deletion lib/matplotlib/tests/test_colorbar.py
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Expand Up @@ -11,9 +11,11 @@
import matplotlib.pyplot as plt
from matplotlib import rcParams
from matplotlib.colors import BoundaryNorm
from matplotlib.colors import LogNorm
from matplotlib.cm import get_cmap
from matplotlib import cm
from matplotlib.colorbar import ColorbarBase
from nose.tools import assert_greater_equal


def _get_cmap_norms():
Expand Down Expand Up @@ -254,7 +256,16 @@ def test_colorbarbase():
ax = plt.gca()
ColorbarBase(ax, plt.cm.bone)


@cleanup
def test_colorbar_lognorm_extension():
# Issue #5201: empty triangle plotted
# for logarithmic colorbar with vmin < 1.0
ax = plt.gca()

cb = ColorbarBase(ax, norm=LogNorm(vmin=1, vmax=1000.0), orientation='vertical', extend='both')

assert_greater_equal(cb._values[0], 0.0)

@image_comparison(
baseline_images=['colorbar_closed_patch'],
remove_text=True)
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