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Storing Images from Cell Array into Different Files

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Eric Martz
Eric Martz on 26 Jul 2019
Commented: Eric Martz on 5 Aug 2019
Hi,
I have already divided a picture into 100 smaller pictures and stored each image in a 10x10 cell array. I am now trying to save them to my computer as a file using imwrite.
[m,n] = size(Pgray);
Blocks = cell(m/100,n/100);
counti = 0;
for i = 1:100:m-99
counti = counti + 1;
countj = 0;
for j = 1:100:n-99
countj = countj + 1;
Blocks{counti,countj} = Pgray(i:i+99,j:j+99);
end
end
I think I need to create a for loop that does this for each cell, but I'm not sure how:
imwrite(Blocks{1,1}, 'Image1.jpg')
I want it to do this for every image of cell array size 10x10 so that it stores them into a folder and is labelled 'Image(1 through 100).jpg'.
Thanks in advance!

  1 Comment

Eric Martz
Eric Martz on 26 Jul 2019
Just to clarify, it's dividing the pictures how I want it to. All i need help with is how to write a for loop to store them in a folder.

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Accepted Answer

awezmm
awezmm on 27 Jul 2019
Here is a for loop that generates a different filename in each iteration:
for i = 1:100
newfilename = strcat('Image', num2str(i), '.jpg')
imwrite(img, newfilename)
end
In this example, strcat combines multiple strings into one string and num2str converts a number to string.
Make sure you are imwriting these files in the correct output directory. An easy way to do this is by putting the path to the output directory in which you want to save stuff, using the cd command, before the for loop.
cd('your_path_to_outputdirectory')

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Eric Martz
Eric Martz on 2 Aug 2019
Yes, they are all different. I tried the mat2tiles and it works the same as my function, so they both return the desired images in a 10x10 cell. I just can't figure out the correct for loop to imwrite them into a folder.
awezmm
awezmm on 3 Aug 2019
Ok I think I understand the problem. Your Blocks Cell is two dimensional and it may be confusing to go through every element. You need to make it into a 1-D vector
First, create the Blocks cell array {} like you normally did.
After that make the Blocks cell one dimension by doing:
oneDBlocks = Blocks(:)
Then you can a for loop easily to write all the images using oneDBlocks
for i = 1:100
newfilename = strcat('Image', num2str(i), '.jpg')
imwrite(oneDBlocks{i}, newfilename)
end
Here is a full example where I take a 100x100 image and divides it into 100 separate 10x10 images and save it in a directory
% making a 100 x 100 image using preloaded Matlab logo image
img = imread('logo.tif');
img = imresize(img, [100 100])
% using mat2tiles to create a cell array that is holding all the subimages that are 10x10 each
Blocks = mat2tiles(img, [10, 10])
% making Blocks into 1D vector
% I think the absence of this is what is causing you trouble
oneDBlocks = Blocks(:)
% making sample output directory
mkdir("example1Dout")
%looping through 1 Dimensional vector and saving each element
cd("example1Dout")
for i = 1:length(oneDBlocks)
newfilename = strcat('Image', num2str(i), '.jpg')
imwrite(oneDBlocks{i}, newfilename)
end
Let me know if you are still having trouble.

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