Poor Image quality when using montage without pauses. How can I check if quality has been lost?

Question

Matteo Parodi 2024-5-10

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https://ww2.mathworks.cn/matlabcentral/answers/2117316-poor-image-quality-when-using-montage-without-pauses-how-can-i-check-if-quality-has-been-lost

回答： Drishti 2024-8-8

I'm using montage to create an image by overlaying two images with transparency. However, I've noticed that the resulting image sometimes appears blurry and of lower quality compared to the original images.

I have notice that pausing before montage (using debug or pause(0.5)) seems to improve the image quality.

since

montage(Im3d,'displayrange',displayrange,'size',size,'indices',indices,'parent',ax);

is different to

pause(0.5);
montage(Im3d,'displayrange',displayrange,'size',size,'indices',indices,'parent',ax);

Searching in the forum I've read that MATLAB switches the renderer to OpenGL for large 3d image, but I don't understand why inserting a pause improves things.

The question are

Is there a way to force montage to use all pixels during rendering, even if it takes longer?

Alternatively, is there a method to determine if MATLAB has resorted to approximations during the process?

Thanks for the help,

Matteo

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Drishti 2024-8-7

I tried to reproduce the code with images of my own but did not see any visible difference. Can you share the code and images that you worked on ?

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Answer 1

Drishti 2024-8-8

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Hi Matteo,

I can conclude that you are trying to utilize the ‘montage’ function, and it seems to reduce the image quality when used without ‘pause’ function.

I tried reproducing the code with sample images and found no visible difference in the quality of image when ‘pause’ function is used with ‘montage’ function. The ‘pause’ function is halting the execution for mentioned period but not altering any pixel value of the image. Whereas ‘montage’ reduces the resolution of the image that leads to the reduction in image quality.

For utilising the complete image during rendering, one work around is to utilize ‘thumbnail’.

% Generate the montage
%f = rand(100, 100, 10); 
%random 3d image can be generated
f = imread('sample_image.jpg'); %sample image is used
img1 = montage(f);
pause(0.5);
img2 = montage(f);
% If you specify an empty array ([]), then the thumbnail size is full size of the image utilized. 
img2 = montage(f,'ThumbnailSize', []);