Pablo Romero wrote:
> This is related to a previous question I had about colormaps;
> Im looking for a method to evenly split up a colormap into an RGB colors
> array.
> something like:
>
> def cmap_to_array(cmap,N):
> ...
>
> mycolors=cmap_to_array(cm.jet,20)
> lev=np.arange(1,20,1)
> cs=contourf(Z,lev,colors=mycolors)
>
> ...
>
> where 'mycolors' would be a 20x3 array with RGB values for 20 colors that
> represent the cm.jet spectrum broken up evenly into 20 colors...
>
> I believe colors array can contain RGB tuples, something like
> [[0.2,0.3,1],[0.3,0.5,1], ... ,[1,1,0]] should work.
>
> However, I dont know how to extract the tuples from an existing colormap.
> How can this be done?
Pablo,
I think that what you want can be handled very simply using the
BoundaryNorm as I have suggested earlier. However, it is not hard to
generate any number of evenly spaced colors (for use in the "colors"
kwarg of contourf). Here is one way to do it:
import numpy as np
import matplotlib.cm as cm
def make_N_colors(cmap_name, N):
cmap = cm.get_cmap(cmap_name, N)
return cmap(np.arange(N))
This will return a sequence of RGBA values, actually an Nx4 ndarray. I
don't think the inclusion of the 4th column hurts anything, but
obviously you can use indexing to remove it if you want to. The last
line in the function would change to
return cmap(np.arange(N))[:,:-1]
cmap_name is a string chosen from the values in cm.datad.keys().
You will want N to be len(lev) - 1.
Eric
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