Re: [Matplotlib-users] create ListedColormap with different alpha values

[Paul I. <piv...@gm...>]

I took a stab at it, how does this look?

I also took the liberty of adding alpha to LinearSegmentedColormap and
updated its docstring changing two somewhat ambiguous uses of the word
'entry' with 'key' and 'value'.

tested with

In [1]: import matplotlib; import numpy as np
In [2]: my_rgba_array= np.array( [[ 1.,  1.,  1.,  0.65],
        [ 1., 0.,  0.,  0.79]])
In [3]: myColormap = matplotlib.colors.ListedColormap(my_rgba_array)

In [4]: myColormap.__call__(.1)
Out[4]: (1.0, 1.0, 1.0, 0.65000000000000002)

In [5]: myColormap.__call__(.9)
Out[5]: (1.0, 0.0, 0.0, 0.790000000000000

In [6]: my_rgba_array= np.array( [         [ 1.  ,  1.  ,  1. ],
       [ 1.  ,  0.  ,  0.  ]])

In [7]: myColormap = matplotlib.colors.ListedColormap(my_rgba_array)

In [8]: myColormap.__call__(.1)
Out[8]: (1.0, 1.0, 1.0, 1.0)

In [9]: myColormap.__call__(.9)
Out[9]: (1.0, 0.0, 0.0, 1.0)


cheers,
Paul Ivanov

John Hunter, on 2008-11-21 05:52, wrote:
> On Fri, Nov 21, 2008 at 2:45 AM, Simon Kammerer <ko...@we...> wrote:
> 
>> After looking at the source of matplotlib.colors, it seems to me that
>> different alpha values are something Colormap is not designed for.
> 
> Yes, it looks like the colormap only holds the RGB channels, but it
> also looks fairly straightforward to patch the code to support the
> fourth channel.  Is this something you'd like to tackle?
> 
> JDH
> 
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