Once we use concatenation function on three images of sizes 64 x 256,128 x 256 and 64 x 256 to get an image of 256 x 256 ,how can we deconcatenate to obtain the same three images back?

a,b and c are three images with dimensions 64 x 256,128 x 256 and 64 x 256

z=cat(1,a,b);

y=cat(1,z,c);

how can we get back a,b,c with same dimensions?