In this paper an intensity based meth od to estimate the parallax between the left and the right image of a stereo pair is studied. Since the simplest intensity based method

i.e. block matching

is sensitive to noise

when small block sizes are required (as e.g. for computer vision purposes)

a new method

improved block matching

based on the non linear diffusion process

was recently developed. It was shown that this new method has better noise suppressing properties than traditional block matching. Here

it is investigated how the new method reacts to a difference in average luminance and contrast of the left and the right image

caused by a gain difference in the left and the right camera. First

it is shown that improved block matching is less sensitive to these differences than traditional block matching. Secondly

a correcting mechanism

called gain control

based on the statistics of the left and the right image of the stereo pair

is shown to improve the performance of the parallax estimating algorithm.