Using CUPS and gimp-print as a Postscript RIPS for a HP 2000CP

The problem

Our old RIP server was an NT4 box and updating it to serve our remaining HP 2000CP was just silly as we intend to replace this plotter with one that has a built in Postscript RIP. Even more annoying was that the proprietary RIP software proved to be based on Ghostscript.

So why pay for Ghostscript? Why mot use it through CUPS?

Alas, the 2000CP is not well represented in the CUPS database, especially the non-postscript version we have. I'd also heard that the result was pretty crummy quality wise. Fortunately a lot of the DesignJet plotters are quite similar, and I figured that something like a DesignJet 2500 driver ought to work. Plus I figured that the RIP manufacturer couldn't have tweaked Ghostscript that much.

The Solution

Settings

I used the HP DesignJet 2500CP PPD, "HP DesignJet 2500CP Foomatic/gimp-print-ijs (recommended)" and installed the HP3500CP PS3 driver on the Windows desktop as the CUPS queue is actually pretending to be a Postscript plotter (even though our plotter is not Postscript). The plotter is shared to the Windows network via Samba.

Issues

Sure enough, the default outout looked decidely average compared to the proprietary RIP. Looking at how CUPS was calling Ghostscript to rasterise the file, I could see a variety of settings that were set to silly defaults.

ps -ef |grep "gs"

Using the CUPS admin interface, http://localhost:631/admin I found that I was able to access many of them, and found that cranking stpGamma right back to 0.8 greatly improved the result. I also bumped default DPI to 600, but am not convinced this had any effect.

The Result

With minimal tinkering, the resulting renders aren't quite as sharp (in terms of vctor linework) as the proprietary RIP, but they are pretty darn close. I'm sure someone more patient would do much better.

Further things to investigate

The default colour model is RGB, Setting it to CMYK might gain much better renders of linework. Plus I'm sure that further tweaking of colour settings and dither algorithms would improve the result even further. Maybe borrow a pantone colour book from our design people and even calibrate the plotter.

Why this document

While this is pretty straight forward, there was a variety of combinations that gave quite poor results, and there was not much information about tweaking CUPS and large plotters to be found, especially for the non-Postscript version of the HP DesignJet 2000CP.