It seems that weskaggs@xxxxxxxxxxxxxxxxxxx has found a way to get a functional script : he added the line (set-output-port p) to initialize the port (which I only implicitly made through the initial call) Now, a working script looks like this : http://tech.ph.groups.yahoo.com/group/script-fu/photos/view/265b?b=1&m=f&o=0 where the new line is indicated with a (ugly) red line. Thanks wesaggs !