This class implements a filterbank for invariant Gaussian derivatives relative to the local gradient (gauge coordinates)
in oponnency Channel space (dark-bright, red-green and blue-yellow opponency).
Does cell c fall within the bounds of a volume for nearest neighbor gradient interpolation?
Bounds are -2...+3 of the cell location (translates to -2...+2 for the voxel location).
ITMAX is the maximum allowed number of iterations; CGOLD is the golden ratio; ZEPS is
a small number that protects against trying to achieve fractional accuracy for a minimum that
happens to be exactly zero.