Orthogonal Functions and Transforms
General representation of image transforms:
where g(m, n, k, l) is the forward transform kernel and h(m, n, k, l) is the inverse transform kernel.
The kernel is said to be separable if g(m, n, k, l) = g1 (m, k) g2 (n, l), and symmetric in addition if g1 and g2 are functionally equal.
Then, the 2D transform may be computed in two simpler steps: 1D row transforms followed by 1D column transforms.