If the channel is linear, Equation 2 may be used to represent the measured intensity level of a pixel in terms of the channel response and the 512 (i.e. 29) possible states of the 3 by 3 neighbor pixels surrounding the central pixel as [ I 1 I 2 ??? I 512 ] = X [ h 1 h 2 h 3 h 4 ] . ( Eqn . 2 ) X is a 512 by 4 matrix, where each row contains the count of the respective terms in h that sum into the