 This GRASS module calculates the 
      Optimum Index factor (OIF)
 for all LANDSAT TM band combinations
 (LANDSAT TM 1,2,3,4,5,7 without termal band 6)

 The result is a ranked list, which shows the
 information content for all possible combinations (20).
 The list is ranked from the best combination down to the 
 combination containing less information.
 From this the user can derive which band combinations
 are interesting to analyse.

 Calculation (after CHAVEZ et al. 1984):

           Sum of Standard deviations of 3 bands
    OIF = ------------------------------------------------
           Sum of ABS(correlation coefficients of 3 bands)


Ref.: Jensen: Introductory digital image processing 1996, p.98
              ISBN 0-13-205840-5

Input: tm1 - tm5, tm7 (not tm6)


Written by Markus Neteler 21. July 1998

(with head/tail corrections from 26. August 1998)

           neteler@geog.uni-hannover.de
