On Tue, Feb 1, 2011 at 5:48 PM, Jeremy Conlin <jlcon...@gmail.com> wrote:
> I'm trying to create a custom colormap used with pcolormesh, but the
> results seem inconsistent to me. I want the following colors
>
> -3 < x <= -2 ----- Black
> -2 < x <= -1 ----- Blue
> -1 < x <= 0 ----- Yellow
> 0 < x <= 1 ----- Green
> 1 < x <= inf ----- Red
>
> A minimal example is copied below. I have a 2-D array that looks like:
>
> -1, 6, 2.5
> 1.3, -2, 4/3
> 2.5, 6, 0
>
> I want to get a pcolormesh that looks like
>
> R R Y
> R K R
> B R R
>
> But instead I get:
>
> Y R B
> Y K Y
> K R Y
>
> I recognize that the pcolormesh is plotted "upside-down" from how the
> matrix is printed. I apparently don't understand how to use a custom
> colormap. I have tried to follow the example here:
>
> http://matplotlib.sourceforge.net/examples/api/colorbar_only.html
>
> but haven't been too successful. It seems like there is a
> normalization going on that I can't seem to track down. Can anyone
> see what is wrong?
>
> Thanks,
> Jeremy
>
>
> import numpy
> import matplotlib.pyplot as pyplot
> import matplotlib.colors
>
> C = numpy.array([[-1,6,2.5],[4/3., -2, 4/3.],[2.5,6,0.0]],dtype=float)
>
> cMap = matplotlib.colors.ListedColormap(['k', 'b', 'y', 'g', 'r'])
> Bounds = [-3.0, -2.0, -1.0, 0.0, 1.0, numpy.inf]
>
> # Plot
> Fig = pyplot.figure()
> pyplot.pcolormesh(C, cmap=cMap)
>
>
Have you given imshow() a try? The pcolor() and family are really meant for
more general domain specifications. imshow() is about as basic as one can
get for producing an image that shows the colors for particular values.
matshow() also does something similar and doesn't interpolate between
points.
I don't know if it would fix your problem, but it should be a good start.
Ben Root
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