SPECTRUM

        [GREG3\]SPECTRUM I [J [K]]

    Extract a spectrum from an image according to the following numbering:
        Spectrum (l) = Image (l,i,j,k)
    for  a  4-dimensional image. The spectrum is loaded into the X,Y buffers
    of GreG. It can be processed later by the standard commands LIMITS, CON-
    NECT, CURVE and so on.