DOCBOOK-APPS: image size control

[Doug du Boulay <ddb@R3401.msl.titech.ac.jp>]

I am using dsssl with openjade and the docbook stylesheets to render html and 
with pdfjadetex to render pdf format.

I would like to know what is the best way to control image sizes in both 
output formats from the docbook markup. 
HTML seems to accept 
width="N" pixels
width="N%" percent
width="N*"  relative dimensions

These dont seem to be honoured by the tex output.
and specifying units of "Ncm" trashes the html output. 

what is the best strategy?


TIA
Doug