Saving a grayscale image with scaled values

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.

[KALYAN ACHARJYA]

Pls attach the image/data, so that we can try on it.

[Jan]

"while not using it produces something like that:" - Please avoid to explain, what you do not do, but mention, what you do to get this image.

Did you try to scale the data by your own?

img = rand(1, 10)

img = 1×10

0.4341 0.8742 0.5018 0.5761 0.0310 0.1867 0.4272 0.2315 0.1484 0.7090

tmp = min(img(:));
img = (img - tmp) / (max(img(:)) - tmp)

img = 1×10

0.4780 1.0000 0.5584 0.6464 0 0.1847 0.4699 0.2377 0.1393 0.8041

[Zinoviy]

Thanks for the replies. I'm including here one of the images as a mat file as @KALYAN ACHARJYA suggested.

I should clarify what I wrote: using imshow(img,[]) produces the second image.

I haven't tried scaling it on my own, but I can try doing what @Jan wrote but I'm note sure how to save it correctly still.

[Zinoviy]

This is the loop I was using to save all the images as png's (but I'm not even sure if that's the right format)

destinationFolder = "directory"

for i=1:100
   name=strcat("rep",string(i),".png")
   fullName = string(strcat(destinationFolder,name)); % replace '.bmp' with the format you want
   imwrite(fisp1(:,:,1,i),fullName)
    
end

[Jan]

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]

Incredible, it worked.

Can you refer me to the explanation of this manual scaling?

Thanks!

Answer 1

[Jan]

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.

[Image Analyst]

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]

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