[texhax] controlling intensity of watermarks

[debian]

Please,

I am trying to design a poster and I was hoping to use a musical score
as a watermark (ie faint in the background of the paper).  So far I
have tried:

\documentclass[24pt,a4paper]{article}
\pagestyle{empty}
\usepackage{eso-pic,graphicx}
\makeatletter
\newcommand\BackgroundPicture[2]{%
  \setlength{\unitlength}{1pt}%
  \put(0,\strip at pt\paperheight){%
  \parbox[t][\paperheight]{\paperwidth}{%
    \vfill
    \centering\includegraphics[angle=#2]{#1}
    \vfill
}}} %

\begin{document}

\makeatother
\AddToShipoutPicture{\BackgroundPicture{/u/lilypond/out/us.pdf}{90}}

........
.........

\end{document}

This works OK, in that it featurs us.pdf as a watermark, but it is too
dark it "dominates" the page too much.  How can I make it appear
lighter ?   Perhaps my approach is wrong ?

Thanks a lot.

Joe