docbook-apps

Hi List.
I want to add some tooling in the html output of my docbook for images,
and thus need to select only some of the ones I have displayed.
So, I have a class/role defined on the imagedata item
<mediaobject>
<imageobject class="imgopen2">
<imagedata class="histogram" role="histogram" align="center"
fileref="{$path}" width="18cm" format="PNG"/>
</imageobject>
...
</mediaobject>
However, when generating the html version, the class is not propagate,
thus



Note, however that the class define on the imageobject is kept.

Is there a way I can have the "histogram" class propagated at the image
level ?

Thanks in advance
Best regards,
Fabien