how can i divide an image into 2 equal parts.horizontaly,?

this code works for 3 equal horizontal parts,how can i change it for 2 parts?

if true
[n,m]=size(im)   % im is your image
id=fix(n/3)
im1=im(1:id,:);
im2=im(id+1:2*id,:);
im3=im(2*id+1:n,:);
end

Answer 1

[Image Analyst]

You can use imcrop, which will work for color and gray scale images:

[rows, columns, numberOfColorChannels] = size(im);
topHalf = imcrop(im, [1, 1, columns, floor(rows/2)]);
bottomHalf = imcrop(im, [1, ceil(rows/2), columns, floor(rows/2)]);

Or if you know for a fact that it's a 2D monochrome image

[rows, columns, numberOfColorChannels] = size(im);
middleRow = floor(rows/2);
topHalf = im(1:middleRow, :);
bottomHalf = im(1+middleRow:end, :);

[sara]

thank you so much,it worked

[Sudeep Albal]

How can i obtain original image from those two parts?

[Image Analyst]

fullImage = [topHalf; bottomHalf];

Answer 2

[vahid rowghanian]

If you want to divide the image into squares of size gs ( e.g. 2,3,4,5,6,7,8,9,10,…), you can use the following code. This function extracts gs by gs patches from the input image and stores them into 'patch' variable. Notice that, if width or height of the input image is not a multiple of gs, then an offset equal to residual of the division won't be covered in patch extraction.

function [ patchim , npatchim ] = divideimage (im , gs)
 imheight=size(im,1);
 imwidth=size(im,2);
maxgsrow =  floor( imheight / gs);
maxgscol =  floor( imwidth / gs );
npatch = 1;
for i = 1 : maxgsrow
  for j = 1 : maxgscol
    rmin = ( i - 1 ) * gs + 1;
    rmax = i * gs;
    cmin = ( j - 1) * gs + 1;
    cmax = j * gs;
%%%%%    do processes
    patch ( : , : , : , npatch) = im( rmin : rmax , cmin : cmax , : );
    npatch = npatch + 1;
  endfor
endfor   
 npatchim = npatch - 1;
patchim = patch;
end