Merge four subbands into 2d image
Q = UpQuad(quad,qmf,xbit,ybit)
quadlet to be joined 4->1 channel
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 split into four channels: (Lo_x,Lo_y), (Lo_x,Hi_y), (Hi_x,Lo_y), (Hi_x,Hi_y) is unsplit into original image.
This routine is called by other, higher-level WaveLab functions and may not be useful for many users.