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

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

Submitter:	Guillaume <gyom>
Submitted:	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
Fixed Release:	None	Planned Release:	None

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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>

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	Category	Plotting with OpenGL	Documentation
		Item Group	Matlab Compatibility	Documentation
		Status	None	Confirmed
		Summary	NaN color with imagesc	Document how NaN color value is handled by imagesc

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

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

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