Images sizing in a PDF

Hello,

There is a big mystery for me : the image sizing !

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<article lang="fr">
    <section>
        <title>Test image scale</title>
        <figure>
            <title>à 100%</title>
            <graphic fileref="Server Admin001.tiff" format="TIFF"
contentwidth="456" contentdepth="569"/>
        </figure>
    </section>
</article>

With this little part of DocBook my image (Server Admin.tiff) is
displayed in my PDF output bigger than the size given (even if I put a
scalefit="1" parameter). Why ?

On the other side, I cannot scale a bigger image (bigger than the page)
with scale parameter.

I know that scale="75" mean "resize the image 75% of the original size",
but it never works with me :-( Is there another parameter ?

Thanks in advance,
Jacques
-- 
AMOUR : mot de cinq lettres, trois voyelles, deux consonnes et deux idiots.