imshow - plotting a circular image, how to make corners white?

Question

Michael 2012-4-26

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Hi

I have a circular image but it's stored as a grayscale matrix, ie. square. When I use "imshow" with the jet colormap it automatically makes the areas outside the circle blue (because the matrix elements are all 0s).

Is there a fix for this? I want the areas outside the circle to be white, or not plotted, without messing with the colormap (which then ruins the colorbar).

Thanks for any help

Mike

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Answer 1

Junaid 2012-4-26

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Could you share your matrix. Or try following command.

colormap gray;

This will make show boundary either black or white.

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Answer 2

Image Analyst 2012-4-26

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Just adjust the colormap:

% Start with the jet colormap.
cmap = jet(256);
% Change 0 from blue to white.
% Gray level of zero will now show up as white rather than blue.
cmap(0,:) = [1 1 1];
% Apply the colormap (a modified jet colormap).
colormap(cmap);

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Michael 2012-4-26

This works, although I have two side-effects, first, the genuine 0 values within the circle appear as white regions (not blue), and also the colorbar is distorted.

I was hoping for an alternative method that doesn't involve this kind of fiddling, because now I have to change the image boundaries and the colorbar properties I think

Thanks for the reply

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