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Changing photo intensity without changes to color map

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adrian leung
adrian leung 2021-12-13
回答： Image Analyst 2021-12-13
Just curious is it possible to change intensity/brightness without making changes to the color map itself?

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回答（2 个）

Chunru
Chunru 2021-12-13
Ran in:
try "brighten":
subplot(121);
I = imread("pout.tif");
imshow(I);
subplot(122)
J = imadjust(I, [0.3 0.7]);
imshow(J)
  1 个评论
adrian leung
adrian leung 2021-12-13
Thanks for the prompt reply.
I saved the final image as uncomrpessed tiff, but its an RGB, not indexed, which defeats the purpose of keeping the original source color map.
Also the dimension is reduced to 893x1273 instead of original 1200x1600.
Is there anyway i can bypass these problems?
Tried using rgb2ind with a colormap (excel table) in variable tab generated from source tiff, however theres error i cant comprehend.
I = imread("sc.tif ");
J = imadjust(I, [0.3 0.7 ]);
K = rgb2ind(J,colormap)
imshow(K)
Error using dither>parse_inputs (line 92)
DITHER(RGB,map): the RGB image has to be a three-dimensional array.
Error in dither (line 47)
[X,m,qm,qe] = parse_inputs(varargin{:});
Error in rgb2ind (line 110)
X = dither(RGB,map);
Error in untitled (line 4)
K = rgb2ind(J,colormap)

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Image Analyst
Image Analyst 2021-12-13
Sure. For a gray scale image you can change it in a variety of ways like adding, subtracting, dividing, using imdjust(), adapthisteq(), etc. Gray scale images don't really have a colormap. When you do that, you're changing the image itself.
Indexed images have a colormap. If you change the image, the values will be different and will now be using a different color from the colormap. So you don't really normally want to do that. You could change the colormap itself, or you could use caxis() to zoom in on a particular part of the colormap and apply just that part. Changing the colormap on an indexed image only changes it's displayed appearance. The image itself does not change - only the colormap.

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