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

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Jon
Jon 2015-7-28
编辑： Jon 2015-7-29
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?
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Image Analyst
Image Analyst 2015-7-29
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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采纳的回答

Jon
Jon 2015-7-28
编辑：Jon 2015-7-29
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...
See http://resources.arcgis.com/en/help/main/10.1/index.html#//009t00000059000000 for what ArcMap is doing.

更多回答（1 个）

Muthu Annamalai
Muthu Annamalai 2015-7-28
Have you tried using a, colormap
>> doc colormap
may help.
  2 个评论
Jon
Jon 2015-7-28
编辑：Jon 2015-7-28
I don't understand why I'd need to create a colormap since the image already contains all the RGB values. The problem is that those RGB values are displaying different (darker) colors in Matlab versus ArcMap, and ArcMap's display agrees with the original data source's (EarthExplorer).
Image Analyst
Image Analyst 2015-7-29
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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