在Matlab中将图像拆分为块

Question

I'm new to Matlab and right now, I'm trying to split an image into NxN blocks as shown in an example below.

In matlab, I'm currently trying something:

my_image = imread('cat.jpg')
figure, imshow(my_image)

nrow = 12; %12 by 12 blocks as shown in the example above.
ncol = 12;

for i =1:nrow
    for j=2:ncol
       block = ...
    end
end

But I'm not entirely sure on how am i supposed to get those lines on the image. I've googled on this but non of them matches what I'm trying to get. Could anyone demonstrate on how is this done?

Answer 1

You don't need to do anything. Matlab's array indexing already supports retrieving and modifying subblocks.

For example, the 2nd 12x12 block is

my_image(1:12,13:24,:)

(I assumed 1 extra dimension for color. I'll let you handle the colors.)

You do not want to re-create the blocks unless you need both the original and the partitioned ones for computation. As much as possible, you want to let Matlab handle the copying and memory allocation.

If you really really need to generate the subblocks explicitly, see mat2cell and also this SO question .

I've googled on this but non of them matches what I'm trying to get.

When you Google, you want to Google the most generic and core concepts. What is an image in Matlab? It is a matrix. What you need is to search how to split a matrix into subblocks. Along this line, search any possible phrase that describes the concept and you will see tons of examples in search returns.

Answer 2

I believe you can use the idea below without the third dimension.

M = magic(4);

N = 2;

x = 1:N;
y = 1:N;

[ X, Y] = meshgrid( x, y);

X = X(:);
Y = Y(:);

ind = sub2ind( size(M), X, Y);
ind = sort(ind);

subM = M(ind);
subM = reshape( subM, [N N])