Image size problems in PDFs

Hi there

When including png images in a DocBook document, they are not scaled to fit
when the output is a PDF. (They are correctly scaled for RTF output).

An example of my figure syntax:
  <figure id="socrates" float="1" pgwide="1">
    <title>A Socrates Question</title>
    <mediaobject><imageobject>
      <imagedata fileref="socrates.png" format="PNG" scalefit="1">
    </imageobject></mediaobject>
  </figure>

I'm using docbook-utils 0.6.12 (jw version 1.1), the DocBook 4.2 SGML DTD
and the DocBook DSSSL Stylesheets 1.78.

What am I doing wrong?

Kind regards
Gary Marshall