equalizer

This program can be used to tonematch or equalize the brightness and/or contrast of the input cubes prior to mosaicking. All cubes must be in a common map projection as this program will use the mapping information to gather statistics in overlapping areas. This is done on a band-by-band basis as well. The statistics are used in a least squares solution to determine multiplicative and additive corrections to each image. The user has the option to stop the processing and examine the statistics and corrective factors. Alternatively, the processing can continue and the corrective factors will be applied to each image (by making sure the APPLY checkbox is ticked). The actual equation to be used for each band in each cube is:

            newdn(s,l,b)   =   (olddn(s,l,b) - avg(b)) * MULT(b) + avg(b) + BASE(b)
        

            s = sample index
            l = line index
            b = band index
        

Prior to equalizing, the user can choose whether to adjust the brightness and/or contrast of the cubes. The default is to adjust both, however, if the brightness (average) of all the cubes is the same, then simply adjusting the contrast may suffice. Likewise, if the standard deviation of all the cubes is similar, then a contrast adjustment is not necessary. Adjusting for contrast only implies the offsets (BASE values) will be held to zero. Similarly, adjust for brightness implies the gains (MULT values) will be held to one.

The BASE and MULT values are computed independently for each image, therefore we have two least squares computations with N unknowns, where N is the number of cubes to be equalized. The overlaps, M, between all the cubes are computed and in some cases M < N. This implies an underdetermined system. The program will report an error if this occurs. You can hold one or more cubes to alleviate this problem. Holding a cube forces MULT and BASE to 1.0 and 0.0, respectively.

If the APPLY option is selected, the equalized cubes will be named the same as the input cubes with the addition of a '.equ' prior to the '.cub' extension.

For the sake of efficiency, the user may choose to set the "sampling percent" to a value less than its default of 100.0. By doing so, the program will likely perform its statistic gathering noticeably faster, but at a potential loss of accuracy in the results. It should also be noted that the user runs the risk of encountering an error if by decreasing the sampling percent, the amount of valid data in their calculated overlaps is less than the minimum set in the MINCOUNT field (default value of 1000). Sampling percent must be a decimal between 0.0 (exclusive) and 100.0 (inclusive).