Re: [Matplotlib-users] Alpha not working from imshow?

[Tim B. <tim...@ma...>]

Thanks, Paul! A bit of tweaking in my actual app but it now works beautifully!

On 18/01/2011, at 4:08 PM, Paul Ivanov wrote:

> Tim Burgess, on 2011-01-18 13:32,  wrote:
>> I'm generating images that I want to use as overlays in Google
>> Earth. Thus, I would like the masked portion of the numpy
>> arrays I am using to appear as transparent.  However, I seem to
>> consistently get white instead of a transparent point.
>> 
>> To clarify the issue, I wrote this short piece of code. I am
>> setting both the figure background to transaprent and the
>> masked value to transparent but I get white.
>> 
>> I have pulled the current svn code and built matplotlib. I get
>> the same issue. 
>> 
>> from numpy import ma
>> import matplotlib.pyplot as plt
>> from pylab import colorbar, imshow, show, cm
>> 
>> 
>> def main():
>>  a = ma.array([[1,2,3],[4,5,6]],mask=[[0,0,1],[0,0,0]])
>>  fig = plt.figure()
>>  fig.patch.set_alpha(0.0)
>>  cmap = cm.jet
>>  cmap.set_bad(alpha=0.0)
>>  imshow(a, interpolation='nearest', cmap=cmap)
>>  colorbar()
>>  show()
> 
> Hi Tim,
> 
> sorry to hear of your troubles - add these two lines to get your
> desired effect:
> 
>  ax = plt.gca()
>  ax.patch.set_alpha(0.0)
> 
> The figure has a patch associated with it, but so does each axes 
> subplot, which is what you were seeing through the transparent
> portion of your masked array image.
> 
> best,
> -- 
> Paul Ivanov
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