See: ``Multi-channel filtering techniques for texture segmentation and
surface quality inspection'',
Farshid Farrokhnia, Ph.D. dissertation,
Michigan State University, Dept. of Elect. Eng., 1990
If any structure specification is given (parameter -s,
-sn or -sb), it is assumed that the input is decimated,
as generated by qmf -d , and each subband is treated
separately (important when scaling is concerned).