帮忙看看这段程序怎么对图像M进行的分块，谢谢！

function patches= compute_patches(M, block_size,step)
% figure
% imshow(M)
M = M(3:end-2,3:end-2);
% % % figure imshow(M)
[r,c]= size(M);%M的尺寸，
if ~exist('step','var')
step = round(max(r,c)/400*block_size);
end
[xc,yc] = meshgrid(0:step:c,0:step:r);tep:c;
%yc是c+1列，元素是0：step：r；
rm_ind = ((xc+block_size)>c)|((yc+block_size)>r);
xc(rm_ind) = [];
yc(rm_ind) = [];
pathch_num = numel(xc);
patches = zeros(pathch_num,block_size*block_size);
for i = 1:block_size
for j = 1:block_size
ind = sub2ind(size(M),yc+i,xc+j);
patches(:,(i-1)*block_size+j) = M(ind(:));
end
end
patches = patches';

其实你只需要理解每个黑白图形都是一个矩阵就行了（0-255），这个Matlab代码都是对矩阵进行各种操作运算。找本Matlab的书看一看吧