2D Down/Up Sampling Operator
DESCRIPTION:
Splits a 2D image into 4 subbands or merge 4 subbands into a 2D image.
USAGE: 
quad.down(x, fl.hor, fh.hor, fl.ver, fh.ver, boundary="periodic")
quad.up(x, fl.hor, fh.hor, fl.ver, fh.ver, boundary="periodic")
REQUIRED ARGUMENTS:
x:
an image or a matrix.
fl.hor:
low-pass quadrature mirror filter for horizontal.
fh.hor:
high-pass quadrature mirror filter for horizontal.
fl.ver:
low-pass quadrature mirror filter for vertical.
fh.ver:
high-pass quadrature mirror filter for vertical.
OPTIONAL ARGUMENTS:
boundary:
a character string giving the name of the boundary rule. All the boundary rules listed for dwt are available except for "infinite". See dwt for the definitions of these rules.
VALUE:
a matrix of the same dimension as x.
SEE ALSO:
convdown , hor.convup , ver.convup.