Say I have four images running west to east, each one overlaps with the ones directly to the east and west: A B C D I want to have them all color balanced using the overlapping zones. I select C as the fixed image, and A, B and D as "Adjust". My question is this: how, exactly, does "A" get color balanced, given that it doesn't actually overlap with C. Does the algorithm first color balance B and D, and then use the overlap between A and the now color balanced B to color balance A? On a related note, what *is* the algorithm used to do the color balancing? Does ENVI calculate regression coefficients using the pixels in the overlap zones, or does it do some sort of adjustment to fit the distribution of values, or what?