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Setting ColorScale to log makes imagesc show wrong colors

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Aurelien Gregor
Aurelien Gregor le 26 Juil 2021
Commenté : Aurelien Gregor le 27 Juil 2021
Hello all !
I've encountered a discrepancy within my imagesc figure between the value of the Index of a point and the color it is supposed to be according to the colorbar within my code.
I managed to reproduce this "error" using a simple script that you can try :
MyImage = pascal(10);
figure
hold on
im=imagesc(1:10,1:10, MyImage);
set(gca,'ColorScale','log')
h = colorbar;
colormap(hsv(5))
As you'll notice some squares do not have the color that it should have according to the colorbar, for example the point [X,Y]=[3 9] has index 45, which should be Yellow according to the colorbar, yet it is in red. Same with [X,Y]=[7 6] with index 462 appears yellow but should be green. There are several other points that have this discrepancy.
When I remove the "set(gca,'ColorScale','log')" line there doesn't appear to be this issue (even more obvious with my original images) so I suspect the error is related to this.
I'm not sure what I've done wrong, I have spent hours ripping my hair over this so any help is much appreciated.
Many thanks.
  2 commentaires
Aurelien Gregor
Aurelien Gregor le 27 Juil 2021
I managed to find an interesting answer here https://fr.mathworks.com/matlabcentral/answers/737702-how-to-get-logarithmic-colorbar-in-matlab-r2012a-for-3d-surface-plot which seems relevant to my issue although I am not sure if I understand it correctly.
Any help in applying this method to my code would be greatly appreciated.
Aurelien Gregor
Aurelien Gregor le 27 Juil 2021
If anybody else is interested it seems Jonathan https://fr.mathworks.com/matlabcentral/answers/203697-logarithmic-scale-for-colorbar has found a decent workaround

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