matplotlib-users Mailing List for matplotlib

On 02/11/2012 10:30 AM, Alexa Villaume wrote:
> Thanks for replying Eric.

(You're welcome. But please keep replies on the list when they are 
potentially useful to others, as yours is.)

>
> Here is my minimal script -
>
> import matplotlib
>
> frompylab import*
>
> import numpy as np
>
> importos
>
>
> metals=np.arange(-3.0, 1.1, 0.1)
>
> U=np.arange(-6.0, 0.25, 0.25)
>
> o3=np.zeros([25,41])
>
>
> plt.contourf(metals, U, o3, levels=[o3col-nsig*o3sig], alpha=0.20,
> colors='blue')
>
> plt.savefig("CoutourPlot.ps")

The Postscript language does not support transparency, so transparency 
is lost when you use the mpl postscript backend.  The way to work around 
this, if you really need to end up with a postscript file, is to save 
the file as pdf, and then use a converter program to render that as 
postscript.  (It might be a "print-to-file" or "save-as" option on your 
pdf display program, for example.  I don't know what is typically 
available on a Mac, but Macs have long been pdf-friendly.  In general, 
the need for ps files has been diminishing.  I almost never generate 
them any more.)

Eric

>
>
> It plots fine except except there is no transparency in colors of the
> contour, it's like alpha is always set to 1.0
>
> On Sat, Feb 11, 2012 at 8:23 AM, Eric Firing <ef...@ha...
> <mailto:ef...@ha...>> wrote:
>
>     On 02/11/2012 07:40 AM, Alexa Villaume wrote:
>      > Hi All,
>      >
>      > I'm just getting started with matplotlib. I'm trying to make a
>     contour
>      > plot using contourf and have the different paths colored and semi
>      > transparent but the alpha keyword doesn't seem to do anything. I
>     googled
>      > around and found that other people have had this same problem but I
>      > didn't find a solution. Here's what I'm doing -
>      >
>      > contourf(metals, U, o3, levels=[o3col-nsig*o3sig, o3col+nsig*o3sig],
>      > alpha=0.20, colors='magenta')
>      >
>      > contourf(metals, U, o2, levels=[o2col-nsig*o2sig, o2col+nsig*o2sig],
>      > alpha=0.20, colors='blue')
>      >
>      > contourf(metals, U, c3, levels=[c3col-nsig*c3sig, c3col+nsig*c3sig],
>      > alpha=0.20, colors='green')
>      >
>      >
>      > To plot them all together.
>      >
>      > For reference my machine is running Mac OS X 10.6.8 and my version of
>      > matplotlib is 1.2.x
>      >
>      > Thanks!
>
>     Please provide a minimal but complete script that illustrates the
>     problem; describe what it is in the output that does not match your
>     expectations.  e.g.,
>
>     import numpy as np
>     import matplotlib.pyplot as plt
>     z = np.arange(20).reshape(4,5)
>     plt.contourf(z, levels=[2,3], alpha=0.2, colors='magenta')
>     plt.savefig("testcontourf_alpha.png")
>
>     which produces a pale magenta stripe, as expected, with mpl from github
>     master.
>
>     Eric

On 02/11/2012 07:40 AM, Alexa Villaume wrote:
> Hi All,
>
> I'm just getting started with matplotlib. I'm trying to make a contour
> plot using contourf and have the different paths colored and semi
> transparent but the alpha keyword doesn't seem to do anything. I googled
> around and found that other people have had this same problem but I
> didn't find a solution. Here's what I'm doing -
>
> contourf(metals, U, o3, levels=[o3col-nsig*o3sig, o3col+nsig*o3sig],
> alpha=0.20, colors='magenta')
>
> contourf(metals, U, o2, levels=[o2col-nsig*o2sig, o2col+nsig*o2sig],
> alpha=0.20, colors='blue')
>
> contourf(metals, U, c3, levels=[c3col-nsig*c3sig, c3col+nsig*c3sig],
> alpha=0.20, colors='green')
>
>
> To plot them all together.
>
> For reference my machine is running Mac OS X 10.6.8 and my version of
> matplotlib is 1.2.x
>
> Thanks!

Please provide a minimal but complete script that illustrates the 
problem; describe what it is in the output that does not match your 
expectations.  e.g.,

import numpy as np
import matplotlib.pyplot as plt
z = np.arange(20).reshape(4,5)
plt.contourf(z, levels=[2,3], alpha=0.2, colors='magenta')
plt.savefig("testcontourf_alpha.png")

which produces a pale magenta stripe, as expected, with mpl from github 
master.

Eric

>
>
>
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Hi All,

I'm just getting started with matplotlib. I'm trying to make a contour plot
using contourf and have the different paths colored and semi transparent
but the alpha keyword doesn't seem to do anything. I googled around and
found that other people have had this same problem but I didn't find a
solution. Here's what I'm doing -

contourf(metals, U, o3, levels=[o3col-nsig*o3sig, o3col+nsig*o3sig], alpha=
0.20, colors='magenta')

contourf(metals, U, o2, levels=[o2col-nsig*o2sig, o2col+nsig*o2sig], alpha=
0.20, colors='blue')

contourf(metals, U, c3, levels=[c3col-nsig*c3sig, c3col+nsig*c3sig], alpha=
0.20, colors='green')


To plot them all together.
For reference my machine is running Mac OS X 10.6.8 and my version of
matplotlib is 1.2.x

Thanks!

Hi,

I am creating a big and complicated plot by doing things like:

ax.add_patch( ... )

and when I'm done I want to save the resulting frame. However, I've 
looked  through
the examples and it seems like you have to use plot() or pcolor() to 
create frames that you
can feed into ArtistAnimation.

So,then, how can I use capture the resulting axes into a frame?

Thanks!