(New slant on) Printing at 1200 dpi from inDesign CS5 to a Xerox colour laser.

Question

I print calendars magazines and stuff like that.
If I use Photoshop CS3~CS5 I can print a 600 dpi photograph to my Postscript 3 enabled Xerox 1200 dpi laser and get quite good appearance of the photo. Even better if I use a 1200 dpi image in the first place but when I use inDesign CS4~CS5 I can't print to the Xerox at anything over 600 dpi. Sure I can place a 1200 dpi image in the document but it still prints at a resolution that looks suspiciously like 300 dpi and the option to print at 1200 dpi is not available to me. I've filled the xerox to capacity with RAM and have a hard drive in it to store popular documents on.
I've explored many ways some associates and posters to these forums have suggested but I still can't get the quality of print from inDesign that I get from Photoshop (or for that matter a popular page layout program from Canada).
The perplexing thing I have yet to find the answer to is:
Commercial printing presses print at 2400 dpi. (let's not confuse the issue here with lpi screens) inDesign is supposedly a professional level program, you'd think would be capable of delivering 2400 dpi output if commercial presses use that resolution. If this is so... Can anyone tell me please how to make inDesign output 2400 or even 1200 dpi?
I've tried distilling the document to a PDF and using pure postscript to no avail. If the printer did not accept 1200 dpi images from Photoshop, I might be tempted to believe it was a printer issue but I'm satisfied it is not. I might point out that I also have an old Minolta (Postscript 3) colour laser too. It produces better quality output than the Xerox but at a huge cost of consumables. I also recognise the Xerox is a LED laser and not the ideal choice for image reproduction but still quite good enough (from Photoshop) for the work it is doing.
Thanks in advance

Answer 1

"John... You seem to be knowledgable in the area of RIPs and platemaking so here's a question you might care to answer. Suppose my platemaker can make a plate at 5080 dpi. (Forget the screening pitch for now) how do send an inDesign document to the platemaker at 5080 dpi resolution? For that matter how do I send any device a document at more than 600 dpi using inDesign? Answer that and you've answered my original question."
ID's "Print Presets" for Postscript output are based on the RIP's PPD.  Since I do not have a RIP connected to my current workstation, the preset defaults to 'device independent'.  The only setting for resolution is the transparency flattener which can be set to "High Resolution".  You should be able to use the Xerox's RIP PPD in the "Print Presets" under File > Print Presets; where the output resolution should be able to be established.  My hunch is, you may have to settle for "High Resolution" and the RIP will output the highest resolution available in the Xerox machine ( if there are no options for resolution in the presets ).
"The only way I can import an indesign PDF into a my pagesetter is to interpolate the images to 1200 ppi seperately from the text and line art which can be 300 dpi or ppi without showing discernable difference. Perhaps your reply in this area was regarding text, not images?"
No.  This is backwards.  Text and line art is set at output resolution ( i.e., 2540dpi ).  You would definitely see a different between 300dpi vs. 2540dpi, especially in small text and the smoothness of lines.  Adobe has a Postscript formula for output resolution. I quote from their Print Publishing Guide "The maximum number of grays that most output devices can produce is 256."  Their Postscript formula is ( output resolution ÷ screen ruling )2 [ squared ] + 1 = shades of Gray.  So, typical offset imagesetter = 2540dpi ÷ 150lpi = 17 x 17 = 289 + 1 = 290 levels of gray.  More than enough to generate smooth blends.  In short, lasers ( or, in your case, LEDs ) typically cannot generate enough resolution to produce what you want.  Which is 1200ppi image resolution(?).  1/1200 LED is about half of what you need for the resolutions you're looking for.
The long and short of it is this.  InDesign is capable of setting its resolution as "High" for raster setting ( i.e., transparency flattener ).  I agree with you it is frustrating that you cannot set the output res anywhere in ID.  I believe that is because it ( the resolution ) is left up to either the RIP or the Print Driver ).
"The perplexing thing I have yet to find the answer to is:
Commercial printing presses print at 2400 dpi. (let's not confuse the issue here with lpi screens)"
No.  The standard is 5080dpi; 2540dpi is minimum ( see my Postscript levels of Gray formula above.  When I prepare an ID file for offset printing, I first have to determine the print vendor's RIP LPi.  This number determines image resolution which, typically is referred to as 2x the LPi.  LPi is ( or should be ) determined by the press itself, the paper, and the inks.  Desktop lasers are totally different.  InDesign does the user a favor by defaulting to device independent so that multiple file do not have to be generated for proofing.  Adobe leaves the print resolutions up to the output device.