Thread: [Matplotlib-users] pcolor

Q: Is it possible to change the default color scale of the
matplotlib.matlab.pcolor plot? How? -Peter

I have been trying to use pcolor() to display a grid with discrete values
(1-4) that are changing over time. I'm generating a series of saved figures
that also include  a line graph of the sums of the 4 categories. The
problem is that that mapping of numbers to colors isn't constant for the
pcolor output. I changed the array from Float32 (used out of habit) to
integer and got the same type of result. It would also be nice to be able
to use the same color mapping for both sub plots. 

I think (guess) that cmap=cm.jet controls the color scheme, but it isn't
clear to me how to change that, what format it has, or why it seems to
change with repeated calls to pcolor() inside the program.

Thanks,

Wendell Cropper


University of Florida
School of Forest Resources and Conservation
214 Newins-Ziegler
PO Box 110410
Gainesville, FL 32611-0410

352-846-0859  phone
352-392-1707  fax

wcr...@uf...

>>>>> "Wendell" == Wendell Cropper <wcr...@uf...> writes:

    Wendell> I have been trying to use pcolor() to display a grid with
    Wendell> discrete values (1-4) that are changing over time. I'm
    Wendell> generating a series of saved figures that also include a
    Wendell> line graph of the sums of the 4 categories. The problem
    Wendell> is that that mapping of numbers to colors isn't constant
    Wendell> for the pcolor output. I changed the array from Float32
    Wendell> (used out of habit) to integer and got the same type of
    Wendell> result. It would also be nice to be able to use the same
    Wendell> color mapping for both sub plots.

    Wendell> I think (guess) that cmap=cm.jet controls the color
    Wendell> scheme, but it isn't clear to me how to change that, what
    Wendell> format it has, or why it seems to change with repeated
    Wendell> calls to pcolor() inside the program.

It sounds to me like the color limits are being autoscaled with each
call to pcolor.  cm.jet does define the color map, but the color
limits define the range of your data that correspond to the min and
max of the colormap.

See help(clim)

If after each call to pcolor, you manually set the clim, you should
have no problems.

JDH



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Thanks very much. Setting clim(0.0, 1.0) inside the loop stabilized the
color mapping.

Wendell Cropper


At 02:58 PM 11/30/2004 -0600, John Hunter wrote:
>>>>>> "Wendell" == Wendell Cropper <wcr...@uf...> writes:
>
>    Wendell> I have been trying to use pcolor() to display a grid with
>    Wendell> discrete values (1-4) that are changing over time. I'm
>    Wendell> generating a series of saved figures that also include a
>    Wendell> line graph of the sums of the 4 categories. The problem
>    Wendell> is that that mapping of numbers to colors isn't constant
>    Wendell> for the pcolor output. I changed the array from Float32
>    Wendell> (used out of habit) to integer and got the same type of
>    Wendell> result. It would also be nice to be able to use the same
>    Wendell> color mapping for both sub plots.
>
>    Wendell> I think (guess) that cmap=cm.jet controls the color
>    Wendell> scheme, but it isn't clear to me how to change that, what
>    Wendell> format it has, or why it seems to change with repeated
>    Wendell> calls to pcolor() inside the program.
>
>It sounds to me like the color limits are being autoscaled with each
>call to pcolor.  cm.jet does define the color map, but the color
>limits define the range of your data that correspond to the min and
>max of the colormap.
>
>See help(clim)
>
>If after each call to pcolor, you manually set the clim, you should
>have no problems.
>
>JDH
>
>
>
>    Wendell> -------------------------------------------------------
>    Wendell> SF email is sponsored by - The IT Product Guide Read
>    Wendell> honest & candid reviews on hundreds of IT Products from
>    Wendell> real users.  Discover which products truly live up to the
>    Wendell> hype. Start reading now.
>    Wendell> http://productguide.itmanagersjournal.com/
>    Wendell> _______________________________________________
>    Wendell> Matplotlib-users mailing list
>    Wendell> Mat...@li...
>    Wendell> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>
>
>


University of Florida
School of Forest Resources and Conservation
214 Newins-Ziegler
PO Box 110410
Gainesville, FL 32611-0410

352-846-0859  phone
352-392-1707  fax

wcr...@uf...

I i have tree lists of values=0Alist x of 100... values=0Alist y of 100.. v=
alues=0Alist mag of 100.. values=0Alist x and y are coordiantes of points =
=0Aand list Mag is magnitude of something at that point=0A=0Ahow can i plot=
 this quantities using pcolor=0A=0Afrom __future__ import division=0Afrom m=
atplotlib.patches import Patch=0Afrom pylab import *=0A=0Adef func3(x,y):=
=0A    return (1- x/2 + x**5 + y**3)*exp(-x**2-y**2)=0A=0A=0A# make these s=
maller to increase the resolution=0Adx, dy =3D 0.5, 0.5=0A=0AX =3D arange(-=
3.0, 3.0001, dx)=0A=0AY =3D arange(-3.0, 3.0001, dy)=0A=0AMag=3D X**2+Y**2=
=0A=0Apcolor(X, Y, Mag, shading=3D'flat')=0Acolorbar()=0Aaxis([-3,3,-3,3])=
=0Asavefig('pcolor_demo')=0Ashow()=0A=0A=0A=0A=0A      ____________________=
________________________________________________________________=0A=A1S=E9 =
un mejor besador!=0AComparte todo lo que sabes sobre besos.                =
      =0Ahttp://telemundo.yahoo.com/promos/mejorbesador.html

The short answer to your two messages is that pcolor and contour 
required gridded data in 2D arrays, and it looks like you are supplying 
1D arrays.  Look at the differences between what you have below and what 
is in the pcolor_demo that you started with.  Meshgrid is generating 2D 
arrays for X and Y so that Z is also 2D.  There are other ways of doing 
it, and for a Cartesian grid, X and Y don't actually have to be 
2D--although I find that there is now a bug in svn such that 1D x and y 
don't work.  I will fix that.  But in any case, Z *must* be a 2D array.

If the data you really want to plot are not already on a grid, then you 
will need to use a gridding routine, which is not included in mpl.

Eric


yadin Bocuma Rivas wrote:
> I i have tree lists of values
> list x of 100... values
> list y of 100.. values
> list mag of 100.. values
> list x and y are coordiantes of points
> and list Mag is magnitude of something at that point
> 
> how can i plot this quantities using pcolor
> 
> from __future__ import division
> from matplotlib.patches import Patch
> from pylab import *
> 
> def func3(x,y):
>     return (1- x/2 + x**5 + y**3)*exp(-x**2-y**2)
> 
> 
> # make these smaller to increase the resolution
> dx, dy = 0.5, 0.5
> 
> X = arange(-3.0, 3.0001, dx)
> 
> Y = arange(-3.0, 3.0001, dy)
> 
> Mag= X**2+Y**2
> 
> pcolor(X, Y, Mag, shading='flat')
> colorbar()
> axis([-3,3,-3,3])
> savefig('pcolor_demo')
> show()
> 
> 
> ------------------------------------------------------------------------
> 
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I would like to use pcolor with the colors going from white (zero
values) to black (largest value).

I am using,

pcolor(a, shading =3D 'flat')
colorbar()

I do not see how to do this.


--=20
"The game of science can accurately be described as a never-ending
insult to human intelligence."=09- Jo=E3o Magueijo

Bryan Fodness wrote:
> I would like to use pcolor with the colors going from white (zero
> values) to black (largest value).
>
> I am using,
>
> pcolor(a, shading = 'flat')
> colorbar()
>
> I do not see how to do this.
>
>
>   
pcolor(a, shading = 'flat', cmap=cm.binary)

-Jeff


-- 
Jeffrey S. Whitaker         Phone : (303)497-6313
NOAA/OAR/CDC  R/PSD1        FAX   : (303)497-6449
325 Broadway                Boulder, CO, USA 80305-3328

On Nov 19, 2007 10:08 PM, Jeff Whitaker <js...@fa...> wrote:
> Bryan Fodness wrote:
> > I would like to use pcolor with the colors going from white (zero
> > values) to black (largest value).

> pcolor(a, shading = 'flat', cmap=cm.binary)

It may not be a binary map you want (that has just two colors) but a
reversed grayscale map which is continuous from white to black, in
which case you would use cmap=cm.gray_r

JDH

John Hunter wrote:
> On Nov 19, 2007 10:08 PM, Jeff Whitaker <js...@fa...> wrote:
>> Bryan Fodness wrote:
>>> I would like to use pcolor with the colors going from white (zero
>>> values) to black (largest value).
> 
>> pcolor(a, shading = 'flat', cmap=cm.binary)
> 
> It may not be a binary map you want (that has just two colors) but a
> reversed grayscale map which is continuous from white to black, in
> which case you would use cmap=cm.gray_r

Agreed, logically it should be cm.gray_r.  But, surprisingly, cm.binary 
  looks identical.  Maybe cm.binary is not doing what you intended it to 
do?  (I have always found LinearSegmentedColormap hard to understand, in 
spite of what seems to be abundant explanation in the docstrings.)

Eric

Dear list,

I have a question concerning pcolor.
I am trying  to plot a huge 2d array 15000x10000.
And in top I see that the program already uses 31Gb of ram and it grows.
Is this expected behaviour?
Why it needs so much memory?
the sctipt is simple:

import matplotlib
import numpy as np
import matplotlib.pyplot as plt

from numpy.random import rand

import mpl_toolkits.basemap as bm 


if __name__ == "__main__":

    print matplotlib.__version__
    print matplotlib.__revision__
    print matplotlib.__date__
    
    
    print 'basemap'
    print bm.__version__
    
    print 'numpy'
    print np.__version__

    
    x = rand(15000,10000)
    #print x
    plt.pcolor(x)
    plt.savefig('test_pcolor.png', bbox_inches = 'tight')
    print "Hello World"

matplotlib version is:
1.0.0
$Revision: 8503 $
$Date: 2010-07-06 08:56:31 -0500 (Tue, 06 Jul 2010) $

should I update?

thank you for any help
--
Oleksandr Huziy
-- 
View this message in context: http://old.nabble.com/pcolor-tp31300362p31300362.html
Sent from the matplotlib - users mailing list archive at Nabble.com.

Ok, it works ok with pcolormesh, sorry for bothering you.

--
Oleeksandr

2011/4/1 sanGuziy <guz...@gm...>

>
> Dear list,
>
> I have a question concerning pcolor.
> I am trying  to plot a huge 2d array 15000x10000.
> And in top I see that the program already uses 31Gb of ram and it grows.
> Is this expected behaviour?
> Why it needs so much memory?
> the sctipt is simple:
>
> import matplotlib
> import numpy as np
> import matplotlib.pyplot as plt
>
> from numpy.random import rand
>
> import mpl_toolkits.basemap as bm
>
>
> if __name__ == "__main__":
>
>    print matplotlib.__version__
>    print matplotlib.__revision__
>    print matplotlib.__date__
>
>
>    print 'basemap'
>    print bm.__version__
>
>    print 'numpy'
>    print np.__version__
>
>
>    x = rand(15000,10000)
>    #print x
>    plt.pcolor(x)
>    plt.savefig('test_pcolor.png', bbox_inches = 'tight')
>    print "Hello World"
>
> matplotlib version is:
> 1.0.0
> $Revision: 8503 $
> $Date: 2010-07-06 08:56:31 -0500 (Tue, 06 Jul 2010) $
>
> should I update?
>
> thank you for any help
> --
> Oleksandr Huziy
> --
> View this message in context:
> http://old.nabble.com/pcolor-tp31300362p31300362.html
> Sent from the matplotlib - users mailing list archive at Nabble.com.
>
>
>
> ------------------------------------------------------------------------------
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>

>>>>> "Peter" == Peter Juvan <pet...@fr...> writes:

    Peter> Q: Is it possible to change the default color scale of the
    Peter> matplotlib.matlab.pcolor plot? How? -Peter

You can define your own colormap by subclassing
matplotlib.colors.Colormap and then passing this to imshow in the cmap
argument.  Note that for the most part pcolor and imshow have the same
functionality, but imshow is 1000 times faster for large grids.
Compare pcolor_demo.py and pcolor_demo2.py in the examples dir which
use pcolor and imshow respectively.  Note, if you really need the
functionality of pcolor over imshow (eg you want to set some
properties on the rectangle patches), I can modify the pcolor argument
list to use your custom colormap.

If you define a new colormap (currently we have only jet and
grayscale), please send it back to the list so I can include it.

JDH

> From: John Hunter [mailto:jdh...@ac...] 
>
> Note, if you really need the
> functionality of pcolor over imshow (eg you want to set some
> properties on the rectangle patches), I can modify the pcolor argument
> list to use your custom colormap.


I prefer pcolor over imshow - I need to represent values from a 12x12 matrix
as colors. Please modify pcolor arguments to use a custom colormap. Where /
when will I be able to obtain the modified version? -Peter

>>>>> "Peter" == Peter Juvan <pet...@fr...> writes:

    Peter> I prefer pcolor over imshow - I need to represent values
    Peter> from a 12x12 matrix as colors. Please modify pcolor
    Peter> arguments to use a custom colormap. Where / when will I be
    Peter> able to obtain the modified version? -Peter

For 12x12 pcolor should work great.  I included the pcolor cmap kwarg
for the next release, which is starting to look like tomorrow rather
than today .....

JDH