matplotlib-users

[Matplotlib-users] specifying NaN color when using imshow

[Gerald J. M. M. <Ger...@jp...>]

Hello,

I'm trying to plot some grid data using basemap and imshow however
haven't figured out how to specify the color for nan values.
For example, in my data, valid values range from 0.0-10.0.  I've
assigned -9999.0 and 1e30 to the missing values and when I imshow
(setting vmin=0.0, vmax=10.0), the missing values show up in the
low and high end of the spectrum, respectively.  Is there a way
to do this?

Thanks,

Gerald

Re: [Matplotlib-users] specifying NaN color when using imshow

[John H. <jdh...@ac...>]

>>>>> "Gerald" == Gerald John M Manipon <Ger...@jp...> writes:

    Gerald> Hello, I'm trying to plot some grid data using basemap and
    Gerald> imshow however haven't figured out how to specify the
    Gerald> color for nan values.  For example, in my data, valid
    Gerald> values range from 0.0-10.0.  I've assigned -9999.0 and
    Gerald> 1e30 to the missing values and when I imshow (setting
    Gerald> vmin=0.0, vmax=10.0), the missing values show up in the
    Gerald> low and high end of the spectrum, respectively.  Is there
    Gerald> a way to do this?

See the archives for a post by Danny Shevitz and followups in the
thread "obscure colormapping issue related to quantization"

http://article.gmane.org/gmane.comp.python.matplotlib.general/2856/match=obscure+colormapping+issue+related+to+quantization

Basically, you want to write a custom normalization and colormapping
instance, and recipe code is posted in the thread linked above.

JDH

Re: [Matplotlib-users] specifying NaN color when using imshow

[Danny S. <sh...@la...>]

I just got back from vacation sorry for the delay.

If you haven't worked out your own solution yet, I took John's suggestions 
and made some very minor additions to them. If you are interested, I can 
post the resulting code which allows you to specify a base colormap and 
then override arbitrary sentinels with specified colors.

One problem with John's algorithm as written in his original post, was that 
the sentinel was included in the normalization and should not be.

D


At 09:21 PM 11/25/2005 -0600, you wrote:
> >>>>> "Gerald" == Gerald John M Manipon 
> <Ger...@jp...> writes:
>
>     Gerald> Hello, I'm trying to plot some grid data using basemap and
>     Gerald> imshow however haven't figured out how to specify the
>     Gerald> color for nan values.  For example, in my data, valid
>     Gerald> values range from 0.0-10.0.  I've assigned -9999.0 and
>     Gerald> 1e30 to the missing values and when I imshow (setting
>     Gerald> vmin=0.0, vmax=10.0), the missing values show up in the
>     Gerald> low and high end of the spectrum, respectively.  Is there
>     Gerald> a way to do this?
>
>See the archives for a post by Danny Shevitz and followups in the
>thread "obscure colormapping issue related to quantization"
>
>http://article.gmane.org/gmane.comp.python.matplotlib.general/2856/match=obscure+colormapping+issue+related+to+quantization
>
>Basically, you want to write a custom normalization and colormapping
>instance, and recipe code is posted in the thread linked above.
>
>JDH
>
>
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Re: [Matplotlib-users] specifying NaN color when using imshow

[John H. <jdh...@ac...>]

>>>>> "Danny" == Danny Shevitz <sh...@la...> writes:

    Danny> I just got back from vacation sorry for the delay.  If you
    Danny> haven't worked out your own solution yet, I took John's
    Danny> suggestions and made some very minor additions to them. If
    Danny> you are interested, I can post the resulting code which
    Danny> allows you to specify a base colormap and then override
    Danny> arbitrary sentinels with specified colors.

    Danny> One problem with John's algorithm as written in his
    Danny> original post, was that the sentinel was included in the
    Danny> normalization and should not be.

I think this would make a nice wiki entry if you get the time.

http://www.scipy.org/wikis/topical_software/MatplotlibCookbook



JDH

Re: [Matplotlib-users] specifying NaN color when using imshow

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

John,

I think that the changes I made in CVS over the weekend provide a much 
easier way to do this, as illustrated in the new examples/image_masked.py.

Eric

John Hunter wrote:
>>>>>>"Danny" == Danny Shevitz <sh...@la...> writes:
> 
> 
>     Danny> I just got back from vacation sorry for the delay.  If you
>     Danny> haven't worked out your own solution yet, I took John's
>     Danny> suggestions and made some very minor additions to them. If
>     Danny> you are interested, I can post the resulting code which
>     Danny> allows you to specify a base colormap and then override
>     Danny> arbitrary sentinels with specified colors.
> 
>     Danny> One problem with John's algorithm as written in his
>     Danny> original post, was that the sentinel was included in the
>     Danny> normalization and should not be.
> 
> I think this would make a nice wiki entry if you get the time.
> 
> http://www.scipy.org/wikis/topical_software/MatplotlibCookbook
> 
> 
> 
> JDH
> 
> 
> -------------------------------------------------------
> This SF.net email is sponsored by: Splunk Inc. Do you grep through log files
> for problems?  Stop!  Download the new AJAX search engine that makes
> searching your log files as easy as surfing the  web.  DOWNLOAD SPLUNK!
> http://ads.osdn.com/?ad_id=7637&alloc_id=16865&op=click
> _______________________________________________
> Matplotlib-users mailing list
> Mat...@li...
> https://lists.sourceforge.net/lists/listinfo/matplotlib-users

Re: [Matplotlib-users] specifying NaN color when using imshow

[Danny S. <sh...@la...>]

I added a Wiki entry entitled "Plotting images with special values". It 
shows my current incarnation of how to plot images with special values 
mapped to specified colors. The user can plot arbitrary numbers of special 
values.

Danny