Case 1: When is

The local contrast of is assumed to be primarily due to and the local contrast of is not alternated.

In this case is approximately the same as ; little processing is done in such regions.

Case 2: If , the local contrast of is assumed to be primarily due to and the local contrast is significantly attenuated.

In this case, is approximately is significantly smoothed

Noting that is identical to when is zero, we can estimate in (6.3.1) from by,

	(6.3.2)

where is the number of pixels in local region used in the estimation.

Within the local region where can be assumed to be space invariant, substitute for in (6.3.1). After same manipulation we get,

where		for            (6.3.3)

,	for
	otherwise.