How to split a large image into many small images?
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Hi, I am working on CNN and I have dataset of large images. I want to split each image into many small images to perform training. Could you please tell me how to do it? To be exact, I want 24 small samples from one 1080 x 1920 image.
Further, is it possible to perform splitting in a imageDatastore? To be exact, I want 24 small samples from one 1080 x 1920 image.
Thanks
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2 Comments
Image Analyst
on 17 Jun 2021
I don't believe imageDatastore() does any image processing -- it's just basically a fancy way of doing dir().
Do you want the samples to be tiled and non-overlapping? Or do you want them taken from random locations?
What I'm confused about is if you're going to use all these small sub-images as training images, how are you going to create your ground truth labels from them?
Accepted Answer
DGM
on 17 Jun 2021
Edited: DGM
on 17 Jun 2021
Blockwise filtering has already been mentioned; since I don't know if that applies to your needs and I have no familiarity with IMDS, I'll just throw this out there.
If you just want to split an image, there are a bunch of ways. You could do it the long way.
inpict = imread('somerandompicture.jpg');
inpict = imresize(inpict,[1080 1920]); % you assert that it's this size
s = size(inpict);
tiling = [4 6]; % i'm assuming this is what you want
f=1;
sout=s(1:2)./tiling;
outpict=zeros([sout,size(inpict,3),prod(tiling)],class(inpict));
for n=1:tiling(2)
for m=1:tiling(1)
outpict(:,:,:,f)=inpict((1:sout(1))+((m-1)*sout(1)),(1:sout(2))+((n-1)*sout(2)),:);
f=f+1;
end
end
In this case, the output is a 4D array. You could use a cell array just the same, though if the goal is to use a cell, you could just do this:
inpict = imread('somerandompicture.jpg');
inpict = imresize(inpict,[1080 1920]); % you assert that it's this size
s = size(inpict);
tiling = [4 6]; % i'm assuming this is what you want
sout=s(1:2)./tiling;
C = mat2cell(inpict,ones(1,tiling(1))*sout(1),ones(1,tiling(2))*sout(2),3)
It's worth noting that both of these will break if your image geometry isn't integer-divisible by the tiling. MIMT imdetile() handles geometry mismatches of the sort, but I doubt you need to deal with it. Just check the geometry and resize as needed.
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More Answers (2)
David Willingham
on 17 Jun 2021
Hi Syed,
I'd encourge you to use blockedImage along with blockedImagedatastore, it will help you perform the block operations for you.
David Willingham
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Sulaymon Eshkabilov
on 17 Jun 2021
Here is a nice discussion on how to split images with nlfilter() suggested by Rik:
1 Comment
DGM
on 17 Jun 2021
To reinforce the distinction, nlfilter() is a rectangular sliding-window filter, whereas blockproc() works on non-overlapping blocks.
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