Is there a "transparent" color, for overlaying contouf regions?

Community matplotlib-users
1

Hello,

(This is a different question for the same project that led me to file a
bug about alpha blending in "contour" .)

I want to overlay a number of exclusion regions in a 2D parameter scan.
I generate each region with contourf in succession, like:

    contourf(x,y,unphys,(1),alpha=1,colors=('w','k'))
    contourf(x,y,excl,(1),alpha=0.5,colors=('w','m'))
    ...

The problem as you might guess is that if I overlay many regions, the
white level at each new region washes out the underlying non-white
colors.

Is there a "transparent" color I can use instead of white? Or, is there
an alternative way to overlay regions that avoids this problem?

Thank you again!

Best,

Sourav

2

Sourav K. Mandal wrote:

Hello,

(This is a different question for the same project that led me to file a
bug about alpha blending in "contour" .)

I want to overlay a number of exclusion regions in a 2D parameter scan.
I generate each region with contourf in succession, like:

    contourf(x,y,unphys,(1),alpha=1,colors=('w','k'))
    contourf(x,y,excl,(1),alpha=0.5,colors=('w','m'))
    ...

The problem as you might guess is that if I overlay many regions, the
white level at each new region washes out the underlying non-white
colors.

Is there a "transparent" color I can use instead of white? Or, is there
an alternative way to overlay regions that avoids this problem?

Until a grand reworking of the alpha mess occurs, here is a (verbose) workaround showing how to set regions to be uncolored (transparent):

In [3]:cs = contourf(rand(10,10), colors=('r', 'g', 'b'))

In [4]:cs.levels
Out[4]:array([ 0. , 0.15, 0.3 , 0.45, 0.6 , 0.75, 0.9 , 1.05])

In [5]:cs.collections
Out[5]:<a list of 7 collections.PathCollection objects>

In [6]:cst = cs.collections[::3]

In [7]:for c in cst:
    ...: c.set_color('none')
    ...:

    ...:

In [8]:draw()

Alternatively, and more simply, why make the transparent regions in the first place?

cs = contourf(rand(10,10), [0.5, 0.7], colors=('b'))

Here we specify a single pair of limits between which the color will be blue.

Eric

3

Hi all,
One of the most persistent problems I have with matplotlib is finding out which kwargs and args are available for some commands.
For instance, I am looking at manipulating axis ticks and labels in mplot3d, so I went to the mplot3d api page, and looked for useful commands and found:

set_xlabel(xlabel, fontdict=None, **kwargs)¶
     Set xlabel.

set_xlim3d(*args, **kwargs)¶
     Set 3D x limits.

However, there is no information that I can find about "args" and "kwargs" that I can use to figure out how to make my changes.

For the record, I want to be able to change the size of the font, the # and values of the tick marks, and to move the axis labels to one or the other end of the axis they are labelling.

Cheers
Michael

4

Well, that's embarrassing -- if I had read the documentation more
carefully, I would have realized that the levels spec "V" means
different things for "contour" and "contourf".

Thank you again! :slight_smile:

Regards,

Sourav

···

On Mon, 2010-02-01 at 15:23 -1000, Eric Firing wrote:

Alternatively, and more simply, why make the transparent regions in the
first place?

cs = contourf(rand(10,10), [0.5, 0.7], colors=('b'))

Here we specify a single pair of limits between which the color will be
blue.

5

Can anyone help?

Michael

···

On 2/1/2010 9:04 PM, Michael Cohen wrote:

Hi all,
One of the most persistent problems I have with matplotlib is finding
out which kwargs and args are available for some commands.
For instance, I am looking at manipulating axis ticks and labels in
mplot3d, so I went to the mplot3d api page, and looked for useful
commands and found:

set_xlabel(xlabel, fontdict=None, **kwargs)¶
      Set xlabel.

set_xlim3d(*args, **kwargs)¶
      Set 3D x limits.

However, there is no information that I can find about "args" and
"kwargs" that I can use to figure out how to make my changes.

For the record, I want to be able to change the size of the font, the #
and values of the tick marks, and to move the axis labels to one or the
other end of the axis they are labelling.

Cheers
Michael

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6

Don't these unbound methods just take the same arguments as the bound
methods "xlabels" and "xlim", as given in

http://matplotlib.sourceforge.net/api/pyplot_api.html#matplotlib.pyplot.xlabel

and

http://matplotlib.sourceforge.net/api/pyplot_api.html#matplotlib.pyplot.xlim

?

···

On Wed, 2010-02-03 at 22:04 -0800, Michael Cohen wrote:

> One of the most persistent problems I have with matplotlib is finding
> out which kwargs and args are available for some commands.
> For instance, I am looking at manipulating axis ticks and labels in
> mplot3d, so I went to the mplot3d api page, and looked for useful
> commands and found:
>
> set_xlabel(xlabel, fontdict=None, **kwargs)¶
> Set xlabel.
>
> set_xlim3d(*args, **kwargs)¶
> Set 3D x limits.
>
> However, there is no information that I can find about "args" and
> "kwargs" that I can use to figure out how to make my changes.

7

Ok, then I guess I am still not seeing how to accomplish what I'm looking to do.
I have a yaxis which has ticks every 0.2, and I need it to be every 0.4.
which function do I use to change that? Can I use that function to change the font size of the tick labels?
It turns out there's an (undocumented) function called set_xticks in the mplot3d api (I deduced its existence from the existence of xticks in pyplot) but I'm not sure how to work it. I thought it would set the values to place the tickmarks at, so I tried:
ax.set_xticks([-0.4,0.0,0.4,0.8])
but that just squashed up the plot.

I also need to move the labels around on the 3d plot so they can be clearly seen in the figure. How can I tell the axis label where to be in reference to the axis itself?

Cheers
Michael

···

On 02/04/2010 02:02 AM, Sourav K. Mandal wrote:

On Wed, 2010-02-03 at 22:04 -0800, Michael Cohen wrote:

One of the most persistent problems I have with matplotlib is finding
out which kwargs and args are available for some commands.
For instance, I am looking at manipulating axis ticks and labels in
mplot3d, so I went to the mplot3d api page, and looked for useful
commands and found:

set_xlabel(xlabel, fontdict=None, **kwargs)¶
       Set xlabel.

set_xlim3d(*args, **kwargs)¶
       Set 3D x limits.

However, there is no information that I can find about "args" and
"kwargs" that I can use to figure out how to make my changes.

Don't these unbound methods just take the same arguments as the bound
methods "xlabels" and "xlim", as given in

http://matplotlib.sourceforge.net/api/pyplot_api.html#matplotlib.pyplot.xlabel

and

http://matplotlib.sourceforge.net/api/pyplot_api.html#matplotlib.pyplot.xlim

?