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How do I limit the range of a colormap when using imwrite

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I want to save an image with imwrite and get the same output as the code below displays on screen
figure,imagesc(rhoi),
colormap(jet)
caxis([.45*min(rhoi(:)) 0*.55*max(rhoi(:))])
Is it possible to set a caxis property for imwrite?
imwrite(rhoi,jet,'out.png')
EDIT: I have included the full code. Basically, I want the last image RGB to look the same as that displayed by imagesc at each stage.
clear all
close all
clc
Inner = 0; % inner radius of the colour ring
rOuter = 150; % outer radius of the colour ring
[x, y] = meshgrid(-rOuter:.1:rOuter);
[theta, rho] = cart2pol(x, y);
rhoi=imcomplement(rho);
cmap=jet(256);
rhoi2=rhoi;
rhoi2=(rhoi2-min(rhoi2(:)))/(max(rhoi2(:))-min(rhoi2(:)));
figure;imagesc(rhoi2),colormap(cmap);
caxis([.55 .95])
rhoi2(rhoi2<.55) = .55;
rhoi2(rhoi2> .95) = .95;
figure,imagesc(rhoi2)
colormap( cmap);
X=uint8(256*rhoi2);
figure;imagesc(X),colormap( cmap);
RGB=ind2rgb(X,cmap);
figure;imshow(RGB)

  3 Comments

Guillaume
Guillaume on 24 Apr 2018

Can you confirm that your rhoi matrix is made of positive integers only. Otherwise, attempting to write an indexed image as per your imwrite call makes no sense.

Michael Devereux
Michael Devereux on 24 Apr 2018
I am scaling the matrix to a range of 0-255 and changing the range accordingly

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Accepted Answer

Guillaume
Guillaume on 24 Apr 2018
Before the call to ind2rgb (or imwrite), you need to rescale your matrix as colour indices so that the minimum is index 1 (for type double, 0 for type uint8) and maximum is index 256 (255 for uint8):
X = round(1 + (rhoi2 - min(rhoi2(:))) * 255 / (max(rhoi2(:)) - min(rhoi2(:)))); %using double
RGB = ind2rgb(X, cmap);
figure; imshow(RGB);

More Answers (1)

Ahmet Cecen
Ahmet Cecen on 23 Apr 2018
You should get the same effect if you just did:
rhoi(rhoi<.45*min(rhoi(:))) = .45*min(rhoi(:));
rhoi(rhoi> 0.55*max(rhoi(:)) = 0.55*max(rhoi(:));

  1 Comment

Michael Devereux
Michael Devereux on 24 Apr 2018
Thanks! This works for viewing with imagesc without specifying caxis but does not work with imwrite or ind2rgb.

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