Saving a grayscale image with scaled values

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Zinoviy
Zinoviy 2022-11-8
编辑： Jan 2022-11-8
Hello, here is my problem:
I have a 196*196 image, and such matrix looks like that for example:
using imshow("img",[]) displays the image correctly because it's scaled, while not using it produces something like that:
I want to save the correct output that should looke like this:
But I can't find the correct parameters for imwrite...
Also I have to say that Im running it with a loop, and planning later on to do image processing, with batch processor and registration and etc.
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Jan
Jan 2022-11-8
folder = "directory"
for i = 1:100
% Scale the image:
img = fisp1(:,:,1,i);
tmp = min(img(:));
img = (img - tmp) / (max(img(:)) - tmp);
% Save the file:
name = fullfile(folder, sprintf('rep%d.png', i));
imwrite(img, name);
end
Zinoviy
Zinoviy 2022-11-8
Incredible, it worked.
Can you refer me to the explanation of this manual scaling?
Thanks!

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Jan
Jan 2022-11-8
编辑：Jan 2022-11-8
folder = "directory"
for i = 1:100
% Scale the image:
img = fisp1(:,:,1,i);
tmp = min(img(:));
img = (img - tmp) / (max(img(:)) - tmp);
% Nicer scaling (Thanks Image Analyst):
% normalize(img, 'range'), or: rescale(img), or: mat2gray(img)
% Save the file:
name = fullfile(folder, sprintf('rep%d.png', i));
imwrite(img, name);
end
If the original values of the image have the range [a, b], so a is the minimal value and b maximal one.
Then img-a has range [0, b-a]. If you divide this by b-a, you get the range [0, 1]. This scales the interval [a,b] to [0,1] to get the maximum contrast.
  2 个评论
Image Analyst
Image Analyst 2022-11-8
Instead of
tmp = min(img(:));
img = (img - tmp) / (max(img(:)) - tmp);
you can use the built in mat2gray
img = mat2gray(tmp);
or use rescale or normalize
Jan
Jan 2022-11-8
Ran in:
Image Analyst's suggestions are smart:
img = rand(1,8)
img = 1×8
0.2261 0.6774 0.9945 0.3414 0.2208 0.1807 0.9315 0.6300
img2 = normalize(img, 'range')
img2 = 1×8
0.0558 0.6103 1.0000 0.1975 0.0492 0 0.9227 0.5521
% Or:
img2 = rescale(img)
img2 = 1×8
0.0558 0.6103 1.0000 0.1975 0.0492 0 0.9227 0.5521
% Or:
img2 = mat2gray(img)
img2 = 1×8
0.0558 0.6103 1.0000 0.1975 0.0492 0 0.9227 0.5521
% Or less nice:
tmp = min(img(:));
img = (img - tmp) / (max(img(:)) - tmp)
img = 1×8
0.0558 0.6103 1.0000 0.1975 0.0492 0 0.9227 0.5521

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