My first answer would be to stop using IDL and move to something better, like python. But, if you can’t, you may be using the default settings for the IDL postscript driver – which specify 4 bits per pixel. You can specify 8 bits per pixel using:

DEVICE, BITS_PER_PIXEL=8

Why this isn’t set to default to 8 in this modern day and age, I don’t know. (And you may be lucky enough to be using IDL 7.1 or greater, which you can set it to 24 bits per pixel). It’s a noticable change when you’re talking about greyscale images. You go from something like this:

The Crappy Version

to something like this:

The slightly better version

It’s not the greatest, but when I get pyastrolib up and running, it’ll be goodbye to IDL forever!

Mubdi