Split 2-d image into 4 subbands
q = DownQuad(Quad,qmf,xbit,ybit)
Quadlet to be split into four subbands
orthogonal quadrature mirror filter
x-position of quadlet in 2-d freq plane
y-position of quadlet in 2-d freq plane
quadlet after splitting
A 2-d signal is split into four subbands: (Lo_x,Lo_y), (Lo_x,Hi_y), (Hi_x,Lo_y), (Hi_x,Hi_y).
This routine is called by other, higher-level WaveLab functions and may not be useful for many users.