read multiple high resolution Images

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Rajesh Acharya 2020-4-21

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评论： Rajesh Acharya 2020-4-22

Hi,

I have a set of 400 images of 1024 x 1024 resolution. I want to open each of the 400 images and extract a perticular row of each image and form a new image out of this. So the resulting number of images will be 1024 each of size 400 x 1024. I need to save these 1024 images separately.

I am able to do this but it is taking more time. I am running a for loop to read/load images from directory one by one, shredding them into a variable of size 1024 x 400 x 1024 size variable. Then running another for loop to save these images.

My question: Is there any better/faster way of doing this (like cell arrays etc or otherwise). Currently it is taking about 80 sec. (intel i-3, win10, r17a).

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Rajesh Acharya 2020-4-22

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Thanks. I am extracting all the 1024 rows. hence 1024 files. Pl refer the code below. How to make it fast.

dir_presino=uigetdir('','Select Directory With Projections');
dir_sino=uigetdir('','Select Directory to Save Sinograms');
presino_file=dir(fullfile(dir_presino,'*.mat'));
[sorted index]=qsort(presino_file,@compfunc); 
presino_image=fullfile(dir_presino,'\',sorted(1).name);
Struct_aligned=load(presino_image);
presino_image=Struct_aligned.shift_image;
[row,column]=size(presino_image);
sinogram=zeros(Np,column,row); % declaring
h=waitbar(0,'Building Sinograms...');
for file=1:Np
    waitbar(file/Np);
    presino_image=fullfile(dir_presino,'\',sorted(file).name);
    Struct_aligned=load(presino_image);
    presino_image=Struct_aligned.shift_image;
    
    for RR=1:row
        sinogram(file,:,RR)=presino_image(RR,:);
    end
end
close(h);
h=waitbar(0,'Saving as files...');
for R=1:row,
    waitbar(R/row);
    string1=num2str(R);
%     Sinogram=(uint16(sinogram(:,:,R)));
%     fname3=[dir_sino,'\Sinogram',string1,'.tif'];
    fname3=[dir_sino,'\Sinogram',string1,'.mat'];
    sino_image=sinogram(:,:,R);
    save(fname3,'sino_image');
%     imwrite(Sinogram,fname3);        
end
close(h);

Bjorn Gustavsson 2020-4-22

My bad missing that line.

sinogram becomes a rather large variable. I encountered similar slowing-downs when some 3-D arrays started to grow. This might be a memmory-issue.

If this becomes "punitively slow" you might have to resort to extracting sinograms from the first half then the second half of your files, and then concateneat the first-half and second-half sinogram-slices together file-by-file. This is an uggly-uggly thing to have to do, but might save you time.

HTH

Rajesh Acharya 2020-4-22