Can anyone say how to divide an image in 6 parts?

I1=I(1:size(I,1)/2,1:size(I,2)/2,:);
I2=I(size(I,1)/2+1:size(I,1),1:size(I,2)/2,:);
I3=I(1:size(I,1)/2,size(I,2)/2+1:size(I,2),:);
I4=I(size(I,1)/2+1:size(I,1),size(I,2)/2+1:size(I,2),:);

This is for dividing a image into four equal parts. Can anyone help me in writing the image into 6 parts (2 row-wise and 3 column- wise) and another for 2 row- wise and 2 column wise. Thank you in advance

Answer 1

[Guillaume]

This is for dividing a image into four equal parts

Yes, and it is horrible! If you start numbering variables you are doing it wrong. A loop or a vectorised method is always better. In your case:

%img: input image
nrows = 2;   %can be whatever you want
ncols = 3;   %can be whatever you want

%some checks first
assert(mod(size(img, 1), nrows) == 0, 'number of rows of image not divisibly by nrows');
assert(mod(size(img, 2), ncols) == 0, 'number of columns of image not divisibly by ncols');

%now divide the image
subimages = mat2cell(img, ones(1, nrows) * size(img, 1)/nrows, ones(1, ncols) * size(img, 2)/ncols, 1)

%all done!

subimages{n} is the same as your original In with the advantage that you can loop over it if needed.

[Jeet Ghosh]

Nice and easy method I guess. I have tested on an image of size 256 x 256. and it is showing "number of columns of image not divisibly by ncols". how to remove this?

[Guillaume]

Depends on what you want to do. You can't divide m into n equal parts if m is not divisible by n. What do you want to do with the left over?

[Guillaume]

This will divide an image into nrows x ncols blocks. If the size is not a multiple of the number of blocks, the last row / column will be larger:

%img: input image
nrows = 2;   %can be whatever you want
ncols = 3;   %can be whatever you want

rowblocks = ones(1, nrows) * floor(size(img, 1) / nrows;
rowblocks(end) = rowblocks(end) + mod(size(img, 1), nrows);
colblocks = ones(1, ncols) * floor(size(img, 2) / ncols;
colblocks(end) = colblocks(end) + mod(size(img, 2), ncols);
subimages = mat2cell(img, rowblocks, colblocks);

[Zara Khan]

Guillaume:

After getting four different and equal parts how can again divide each of these parts to 4 equal parts and so on. This process will continue as long as we can get 4 equal size parts?

[Guillaume]

Instead of an iterative process, you can figure out straight away how many times you can divide the image into equal parts. It's how many times you can divide the width and height by 2. So:

%img: input image. To be divided in blocks of equal size
nrows = nnz(factor(size(img, 1)) == 2);
ncols = nnz(factor(size(img, 2)) == 2);
subimages = mat2cell(img, ones(1, nrows) * size(img, 1)/nrows, ones(1, ncols) * size(img, 2)/ncols, 1);

Answer 2

[Image Analyst]

FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_split_an_image_into_non-overlapping_blocks.3F