Saved Matrix as Image does not give me the right pixels

Hi there,

currently I am trying to save a (100 x 100) matrix in one .tif image.

When opening this image, it occurs that it has 1200 x 900 pixels eventhough it should be 100 x 100.

    
    Nsub = 100
    Q = reshape(Isub(:,:,is)(:,j),[Nsub,Nsub]); % Q has the size of 100 x 100.
    
    % Output data as a figure
    figure()
    
    %set_x_axis = [ -Nsub Nsub]; 
    %set_y_axis = set_x_axis

    imagesc(Q);
    newmap = contrast(Q); % Change into greyscale
    colormap(newmap);
    set(gca,'XTick',[], 'YTick', []);
    save_in_folder = "C:/Users/TestImages";
    file = sprintf("%s/%dmm/tif/%03d.tif", save_in_folder, List_of_foldernames(is),k);
    saveas(imagesc(Q), file);

Has anyone an idea why?

Answer 1

[Subhadeep Koley]

Hakan, you are getting a 1200-by-900 image because you're saving the entire figure window in the tif file. If you only need to save the image, refer the code below,

nSub = 100;
% Creating a random image
img = rand(nSub);

% Visualize the image
figure
imagesc(img)
newMap = contrast(img);
colormap(newMap);

% Write the image and its associated colormap
imwrite(im2uint8(img), newMap, 'yourFile.tif')

[Hakan Östen]

Thanks for your answer. I see this makes sense.

I somehow get trouble by using im2uint8. My system crashes and I do not know why.

However maybe to shortcut it these image formation processes - I could just save my Q matrix as a tif file with

saveas(Q, file) % whereas Q is my 100 x 100 integer matrix

Here, I do get a handle graphics error...

[Subhadeep Koley]

@ Hakan Östen If im2uint8 is not working then you can use the code below,

imwrite(rescale(img, 0, 255), newMap, 'yourFile.tif')

[Hakan Östen]

When Q is outputted as a figure in a popup, it works fine.

It seems that imwrite does not work properly. The image is stored empty. No information seems to get out.

Edited: I found the issue. The matrix did not have a scale of 0 255 pixels. I used

uint8(255*mat2gray(Q))

to fix it.

Thanks Subhadeep.

[Subhadeep Koley]

@ Hakan Östen You tried this?

imwrite(rescale(img, 0, 255), newMap, 'yourFile.tif')