Re: Illustrations to be printed; was: Re: Viso/Office guru?

Subject: Re: Illustrations to be printed; was: Re: Viso/Office guru?
From: David Neeley <dbneeley -at- gmail -dot- com>
To: techwr-l -at- lists -dot- techwr-l -dot- com
Date: Tue, 8 Sep 2009 10:36:47 +0300

From: "Gene Kim-Eng" <techwr -at- genek -dot- com>
To: <techwr-l -at- lists -dot- techwr-l -dot- com>
Date: Mon, 7 Sep 2009 02:38:14 -0700
Subject: Re: Illustrations to be printed; was: Re: Viso/Office guru?
Our most common printed output is from Xerox DocuTech (600x2400 black,
600x600 color). Color covers are printed at 400 lpi. We find source
quality at any dpi below 600 for pages and 1200 for covers produces
unacceptable results.

Gene Kim-Eng


As you know, the DocuTech is a very large laser printer. When you say
the color covers are printed at "400 lpi" that would seem to indicate
they are being offset printed and inserted into the page stream for
binding. If so, 400 lpi would be far higher than you probably need.
Even 300 lpi offset color would be far higher than most book covers
use. If your cover contains photographs with a high degree of contrast
between light and dark areas, I suppose that might be one reason to go
that route--but it would be overkill for most such covers.

If, on the other hand, the covers are also being printed on the
DocuTech (which would technically be in a dpi rating rather than lpi),
it would be a somewhat different story.

(To clarify the "dpi" vs. "lpi" issue a little--laser printers use
tiny, discrete dots in the print, corresponding to pixel information
on a computer screen as a good way of thinking about them. By
contrast, offset printing uses a mesh screen--originally it was made
of very fine silk cloth. The offset process produces its bits of ink
in the "holes" in the screen. The area between the holes--which was
originally the threads of the silk cloth--were the "lines" we speak of
when we talk about "lpi" in offset resolution. Today, of course, the
screens are not cloth in offset printing--although they remain,
obviously, in another printing technology--silk screen printing, in

As I said originally, the input resolution for a laser printer should
at least match the output resolution as closely as possible. In most
machines, a resolution like "600 x 2400" means there is a stepper
motor somewhere involved, pulling the paper vertically to give a
higher effective vertical resolution. I have no idea about the current
generation DocuTech, although they were designed and built in El
Segundo--the first generation was launched while I was consulting
there, in fact.

(Interestingly, the first generation DocuTech used, IIRC, six or eight
different processors--they were Xerox' proprietary "Mesa" processors
as used in their 6085 workstations in those days. Each had a whopping
1 MIP of processing power. I am sure they have long since moved to
more powerful chips--in fact, they had working prototypes before I
left using Sparcstations as their RIPs that far outperformed anything
then available. Their first commercial color laser printer was a
failure--and it was replaced with a faster machine that originally was
developed using an off-the-shelf 486 under the cabinet!)

Because your black and white pages are using a 600 dpi laser, it
stands to reason that your input should be at least that resolution.
For the color, the RIP is working to separate the colors into CMYK,
and the process requires a large amount of information for the RIP to
work with. Often, the originals from PCs are created in RGB; it isn't
just a matter of resolution. Conversion algorithms between RGB and
CMYK are often not perfect by a long shot.

(This is why the Mac has always had an edge in color offset
printing--its color model has been CMYK, as I understand it).

Vector graphics are another issue, as Mats has stated. Very often,
vector art has very sharp edges to its lines and shapes. The version
submitted in a file to be printed, though, has been rendered into
raster form. The RIP can use the best available resolution to form its
output image--which is why higher resolution input may be helpful. If
a RIP could use a pure vector original, resolution would be a complete
non-issue--it would automatically produce its image at the maximum
native resolution.


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