how to enlarge the blocks in subplot

i've a grayscale image 0f size 256x256 and i've divided it into 16x16 blocks

i've ploted this with the function subplot like

      subplot(16,16,blockNumber);
      imshow(oneBlock);

this shows all the 256 blocks in total. by looking at these blocks i cant identify the blocks as these are very small

http://imageshack.us/photo/my-images/23/missileb.jpg/

the above link is corresponding to my image and here in this image the blocks are very small..

 how can i visualize these blocks?