How to work with some part of matrix only?

I have several tif images. their size is big and I get a memory error for that. Thats why I decieded to select a part of them and do my operation on that part only to avoid memory error.could this be a solution and how can I do it?

L = imread('lc60_4.tif'); 

s =imread('s240_4.tif'); 

c =imread('c240_4.tif'); 

S =imread('ts4_240.tif'); 

S5 =imread('td4_240.tif');
[x,y] = size(L);

Answer 1

[VIJENDRA]

you can use 'imcrop' to crop some part of the image.

croppedIm = imcrop(yourImage);

[Hana]

How to define the extent of the matrix?

Answer 2

[Walter Roberson]

Depending on what you are doing, you may be able to use the "src_filename" version of blockproc()

imcrop() is the same thing as indexing the image array to extract a portion of it: it still requires that you read in the entire image.

With TIFF files, if your image has been created the right way, you may be able to use the TIFF Class to read "tiles": see http://www.mathworks.com/help/matlab/ref/tiff.readencodedtile.html