Hi, developers. I stumbled upon this when I noticed that gist_stern_r isn't
the reverse of gist_stern. As the attached script shows, the discontinuity in
red is wrong, and green stays zero instead of ramping. The problem seems to be
that when cm.revcmap() reverses a linear segment map spec (such as {'red':
[(0, 0, 0), (0.5, 1, 1), (1, 1, 1)], ...}), it doesn't swap the second and
third elements of each tuple-the color values facing in each direction. That
makes no difference for continuous colormaps but distorts discontinuous maps
such as gist_stern. I believe that the attached "cm.patch" file fixes the
problem.The other patch, "_cm.patch", is only aesthetic after the above patch is applied. It changes an element of the gist_stern colormap spec that should have been unused but which caused the green channel to stay at zero with the old revcmap. With the patched revcmap, the changed element should not be used, but the colormap spec will look like most others with the second and third elements of the tuple being equal.
import matplotlib as mpl
import matplotlib.pyplot as plt
import matplotlib.cm as mcmap
import numpy as np
def show_cmap_rgb(cmap, axes):
x = np.linspace(0, 1, 256)
rgba = cmap(x)
lines = []
for (idx, color) in enumerate('rgb'):
lines.extend(axes.plot(x, rgba[:, idx], ':', color=color))
axes.set_xlim(0, 1)
axes.set_ylim(-0.1, 1.1)
return lines
fig = plt.figure()
axes_f = fig.add_subplot(2, 1, 1)
show_cmap_rgb(mcmap.gist_stern, axes_f)
axes_f.set_title('Forward')
axes_r = fig.add_subplot(2, 1, 2)
show_cmap_rgb(mcmap.gist_stern_r, axes_r)
axes_r.invert_xaxis()
axes_r.set_title('Reversed')
cm.patch
Description: Binary data
_cm.patch
Description: Binary data
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