EXTRACT

        EXTRACT

    Extracts  a  subset  of  an  input  image.   The  output  image  can  be
    larger  than  the subset; in this case the additional pixels are blanked
    if the output image is being created, unmodified if it  already  exists.
    It  works on images of any dimensions, and any subset of the input image
    can be placed anywhere in the output image.  This routine  can  also  be
    used  to build a N+P dimensional image from a set of N dimensional ones,
    by initializing the output image once with its full dimensions and  then
    placing the (subset of the) input images at the appropriate place in the
    output image.