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Why is my RGB image not displaying as expected using imshow?

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Jon
Jon on 28 Jul 2015
Edited: Jon on 29 Jul 2015
I have a Landsat "natural" image with three color bands (rgb values ranging from 0-256). When I display the image in ArcMap, it looks correct:
However, when I display the image in Matlab with the following code:
[I, cmap] = imread('imname')
imshow(I)
(cmap is empty, I is M x N x 3 uint8)
the resulting image is
It appears to be drawing from all three color bands, but the coloration is much different than what I expect (i.e. what ArcMap and Landsat's website display). Does anyone have any ideas about how to get Matlab to display the image like Arcmap?
  5 Comments
Image Analyst
Image Analyst on 29 Jul 2015
It can be confusing. No scaling takes place with uint8 RGB images so imshow(), imshow([]), and imagesc() all produce the same thing:
% Read in standard demo image and make it dark by dividing by 4.
rgbImage = imread('peppers.png') / 4;
% Display 3 different ways.
subplot(1,3,1);
imshow(rgbImage)
title('imshow(rgbImage)', 'FontSize', 20);
subplot(1,3,2);
imshow(rgbImage, [])
title('imshow(rgbImage, [])', 'FontSize', 20);
subplot(1,3,3);
imagesc(rgbImage)
title('imagesc(rgbImage)', 'FontSize', 20);
axis image;

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Accepted Answer

Jon
Jon on 28 Jul 2015
Edited: Jon on 29 Jul 2015
The problem here is that I was expecting the wrong thing. Matlab is plotting the proper RGB values; ArcMap was automatically applying a "gamma stretch" unbeknownst to me. Now off to figure out how to Matlab a gamma stretch...

More Answers (1)

Muthu Annamalai
Muthu Annamalai on 28 Jul 2015
Have you tried using a, colormap
>> doc colormap
may help.
  2 Comments
Image Analyst
Image Analyst on 29 Jul 2015
That's incorrect. Color maps are not used and don't apply when an RGB image is displayed as Jon said.

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