IMSHOW(I,[LOW HIGH]) displays I as a grayscale intensity
image, specifying the data range for I. The value LOW (and
any value less than LOW) displays as black, the HIGH (and any
value greater than HIGH) displays as white, and values in
between display as intermediate shades of gray. IMSHOW uses
the default number of gray levels. If you use an empty matrix
([]) for [LOW HIGH], IMSHOW uses [min(I(:)) max(I(:))]; the
minimum value in I displays as black, and the maximum value
displays as white.