bugGNU Octave - Bugs: bug #58325, Document how NaN color value is...

 
 

bug #58325: Document how NaN color value is handled by imagesc

Submitted by:  Guillaume <gyom>
Submitted on:  Thu 07 May 2020 04:47:41 PM UTC  
 
Category:  Documentation Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Documentation
Status:  Confirmed Assigned to:  None
Originator Name:  Guillaume Open/Closed:  Open
Release:  dev Operating System:  Any

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Tue 12 May 2020 10:14:03 PM UTC, comment #1: 

I think it would be fine to add documentation that Octave uses black for NaN values in imagesc.  Also, you might want to document the workaround of using pcolor.

pcolor (x)
shading interp
set (gca, 'color', DESIRED_COLOR_FOR_NAN_VALUES)

Rik <rik5>
Project Administrator
Thu 07 May 2020 04:47:41 PM UTC, original submission:  

When displaying an image containing NaNs with imagesc, Octave displays them as black while Matlab uses the first color of the colormap.

I could find a related comment on the Octave Help mailing list:
https://lists.gnu.org/archive/html/help-octave/2018-10/msg00059.html
and it seems to be frequently mentioned by Matlab users:
https://stackoverflow.com/questions/14933039/matlab-imagesc-plotting-nan-values
https://stackoverflow.com/questions/8481324/contrasting-color-for-nans-in-imagesc
https://www.mathworks.com/matlabcentral/answers/373508-imagesc-how-to-set-nan-as-white-color
https://www.mathworks.com/matlabcentral/answers/81938-set-nan-as-another-color-than-default-using-imagesc

Now, the Matlab documentation says: "The behavior of NaN elements is not defined."
https://www.mathworks.com/help/matlab/ref/imagesc.html#buxkjup-2l
so there is no need to try and reproduce an undefined behavior. But could the documentation be updated to either say that the behavior is unpredictable or that a black color will be used?

Guillaume <gyom>

 

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    Follow 4 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2020-05-17 rik5 CategoryPlotting with OpenGL => Documentation
        Item GroupMatlab Compatibility => Documentation
        StatusNone => Confirmed
        SummaryNaN color with imagesc => Document how NaN color value is handled by imagesc

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