Default settings for convert

Hello,

it seems that from ImageMagick-6.3.5.10 (approximately) convert utility has a different
default settings for postscript conversions (gentoo linux here).

This causes some problems in case some scripts call convert internally and get
different versions of output, see http://bugzilla.lyx.org/show_bug.cgi?id=4749 .

It would be good if there is a way how to write the script so it behave in the same
way for a different versions of Imagemagick. In case you can reproduce this behaviour
I would like to ask what parameters should be used so one gets backward compatible
script which will also work for next releases.

Regards,
Pavel