
negative to indicate shifting upward.

<p>The overlay need not fit entirely (or at all) on the underlying image.
<B>pamcomp</B> uses only the parts that lie over the underlying image.

<P>Before Netpbm 10.10 (October 2002), <b>-xoff</b> was mutually 
exclusive with <b>-valign</b> and always measured from the top edge.

<DT><B>-alpha=</B><i>alpha-pgmfile</i>
<DD>
This option names a file that contains the alpha mask.  If you don't
specify this option, there is no alpha mask, which is equivalent to 
having a