Re: [Matplotlib-users] Alpha keyword not working with contourf

[Eric F. <ef...@ha...>]

On 02/11/2012 10:53 PM, Alexa Villaume wrote:
> (Sorry about not replying to list before. I usually have to be pretty
> vigilant about not clicking "Reply-All")
>
> I made my figure a pdf and the transparency works fine. So thanks! Just
> another quick question is it the Postscript language itself that doesn't
> support transparency or the way mpl handles postscript files?

It is the language itself.

Eric

>
> On Sat, Feb 11, 2012 at 10:48 AM, Eric Firing <ef...@ha...
> <mailto:ef...@ha...>> wrote:
>
>     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...>
>         <mailto: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
>
>