At short wavelengths, the adjacency correction causes strange effects at borders
For geocoded imagery the number of adjacency zones should be set to N=1.Reason: The problem with adjacency correction at image borders is that information outside the scene is required, as the algorithm employs a moving window corresponding to twice the adjacency range, centered on each pixel.So an assumption is needed to estimate this missing information. If you set N=2 (or any N > 1) the program will calculate the average reflectance in two zones, and the outer zone in touch with the geocoded background will generally have a different average reflectance than the inner zone, even if a reasonable assumption for the background reflectance is being made (e.g. average nonbackground scene reflectance). For longer wavelength bands the influence of the adjacency effect decreases, so the effect cannot be seen.So our recommendation is to use N=1 for geocoded data. However, you can use up to N=5 and compare it to N=1 results, but you have to omit the scene borders for a quantitative evaluation. Then you will find that the effect of N=1 versus N=5 or N=2 is usually very small.
