y.  Anything in between is
translucent.  (Like any Netpbm program, <B>pamcomp</B> will see a PBM
file as if it is PGM).

<p>If the overlay image is a PAM image of tuple type RGB_ALPHA or
GRAYSCALE_ALPHA, then the overlay image contains transparency
information itself and <b>pamcomp</b> uses it the same way as the
alpha mask described above.  If you supply both an overlay image that
has transparency information and an alpha mask, <b>pamcomp</b>
multiplies the two opacities to get the opacity of the overlay p