Printtool indicates 300x300 as maximum resolution of the driver for HP
deskjets 550C/56C/6xxC series (this is the driver that works for most 800
and 900 inkjets). This is misleading : resolutions up to 600x600 can be
obtained by adding -r600x600 in the options. Not a big issue, but we could
have produced better slides in the past!
Are you sure the original 550 can do 600x600? I don't think it could.
We can add an extra entry for printers supporting it though, if the 550 can't -
what printer are you using?
I am using a 970Cxi. I don't know about old 550C/56C/6xxC HP deskjets (I guess
they did not support more than 300x300 resolution). I think that all newer
printers (series 8xx and 9xx) support at least 600x600, and often more.
In 1.75, the hpdj driver is marked as supporting 300x300, 300x600 and 600x600.