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Are developers of matplotlib planning to implement something like this:
http://www.pyngl.ucar.edu/Examples/Images/ngl04p.2.png ?
Thanks.
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On Fri, Oct 1, 2010 at 8:59 PM, Stan West <sta...@nr...> wrote:

>  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.
>
>
I can confirm the bug, but I have not tested the patch.

Ben Root

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')