Re: Alpha keyword not working with contourf
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 <efiring@...
> <mailto:efiring@...>> 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 <efiring@...
> <mailto:efiring@...>
> <mailto:efiring@...
<mailto:efiring@...>>> 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
>
>
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