MATLAB: Dividing image into 2×2 blocks and calculating SSIM for each block.

Image Processing Toolboxssim

Hey,

I'm trying to compare two images. I need to break each image into 2×2 blocks and come compare each block using the SSIM function Thanks

Best Answer

Assuming that the size of the image is a multiple of the window size (which as Image Analyst pointed out probably needs to be bigger than 2x2):

%img1, img2: images to compare
blocksize = [2 2];  %should probably be [8 8]
rowdist = ones(1, size(img1, 1)/blocksize(1)) * blocksize(1);
coldist = ones(1, size(img1, 2)/blocksize(2)) * blocksize(2);
ssimblocks = cellfun(@ssim, mat2cell(img1, rowdist, coldist, size(img1, 3)), ...
                            mat2cell(img2, rowdist, coldist, size(img2, 3)))

Related Solutions

MATLAB: Can anybody please help me to do the following

You can use mat2cell to divide a matrix into submatrices:

img = uint8(randi([0 255], 206, 100, 3)); %for example

n = 10; %for example
rowdist = n * ones(1, ceil(size(img, 1) /  n));
rowdist(end) = size(img, 1) - sum(rowdist(1:end-1)); %in case n is not a divisor of the image height
coldist = n * ones(1, ceil(size(img, 2) /  n));
coldist(end) = size(img, 2) - sum(coldist(1:end-1)); %in case n is not a divisor of the image width
subimgs = mat2cell(rowdist, coldist, size(img, 3))

To convert the cell array of matrices to a cell array of vectors:

subimgv = cellfun(@(m) m(:), subimgs, 'UniformOutput', false)

MATLAB: Divide an image to overlapped blocks

nadia - if you want to extract every 31x31 block, then you could try using blockproc from the Image Processing Toolbox, or you could try the following (which should work though is not necessarily that efficient). Create a cell array for all of your distinct blocks as

 blockSize = 31;  % assumed square

 imageSize = 512; % assumed square
 blockArray = cell(imageSize - blockSize +1);

Now iterate over each 31x31 block as follows

 for r=1:size(blockArray,1)
     for c=1:size(blockArray,2)
         blockArray{r,c} = myImage(r:r - 1 + blockSize, ...
                                   c:c - 1 + blockSize);
     end
 end

where myImage is your 512x512 image. Note how we move the sliding window across each row r and column c.

Best Answer

Related Solutions

MATLAB: Can anybody please help me to do the following

MATLAB: Divide an image to overlapped blocks

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