1. An image transform method, comprising: (a) first filtering an input two-dimensional real-valued digital image with respect to a first dimension, said first filtering including a first lowpass filtering to yield a lowband and a first highpass filtering to yield a highband; (b) second filtering said lowband from step (a) with respect to a second dimension, said second filtering including a second lowpass filtering to yield a low-lowband and a second highpass filtering to yield a high-lowband; and (c) third filtering said highband from step (a) with respect to said second dimension, said third filtering including a third lowpass filtering to yield a low-highband, a third highpass filtering to yield a first high-highband, and a fourth highpass filtering to yield a second high-highband, wherein said third and fourth highpass filterings have impulse response z-transforms as complex conjugates.