output = ComputeGammaExtP(x,input)
Compute the gamma table using an extended power function.
See Brainard, Pelli, & Robson (2001).
Largest value in input must be the maximum device
setting. This is wise during measurements in
9/21/93 dhb,ccc Added checks for parameter bounds.
10/3/93 dhb,jms Normalize output to max of 1.
Better be sure that last value is max setting.
8/7/00 dhb Rewrote equation this uses completely.