From: "Michael Fox Photography News Account" <email@hidden>
Date: Mon, 15 Aug 2005 08:52:05 -0700
Some time ago, one of the Epson tech support people told me that
the "internal" resolution of the current printers (2200, 4000,
7600, 9600) was 360 ppi. In other words, if it received an image
with something other than this resolution, it would interpolate it
to 360, then go about it's process of creating variable-sized dots,
etc.
I hope it doesn't do this with text and line art. 360 DPI is way too
low to get really crisp text. It's probably fine for photos, though.
I have also heard from people who have the time to do such tests
that they can see differences in the output up to 360 ppi. But
higher resolution files produce no discernable difference in
output. This would seem to be real-world evidence of what the tech
support guy said.
Using Gimp-Print/Gutenprint (disclaimer: I'm the project lead) I can
see differences in the CUPS test page (which has a very extreme
example of this: a circle of 360 very narrow radial lines spaced 1
degree apart) even going from 1440x720 to 1440x1440 DPI on the Stylus
C80: at 1440x720 there's noticeable stair stepping, while at 1440x1440
DPI there's very little. There's a visible difference even at
2880x1440 DPI, but that's due to moire effects from the extremely fine
lines.
It would be interesting to try the same experiment on the R800, going
from 2880x1440 to 2880x2880 to 5760x2880 (yes, that printer can print
at those resolutions -- and 5760x2880 is amazingly smooth -- but it's
very, very slow at 2880x2880 and above!).
Gimp-Print and Gutenprint (Gutenprint is the name for the next major
release of Gimp-Print) don't downsample the input unless the input
resolution is higher than the printing resolution (which is generally
a very bad thing to do -- it drops pixels). If the input resolution
is lower than the printing resolution it duplicates pixels as
necessary, so you want the printing resolution to be a multiple of the
input resolution if you can.
For printing photos or other smooth tone work I doubt it matters very
much. Even for text you probably won't see much in the way of jaggies
with an input resolution of 720 DPI or better. But there are examples
(even if highly contrived) where it does make a difference.
--
Robert Krawitz <email@hidden>
Tall Clubs International -- http://www.tall.org/ or 1-888-IM-TALL-2
Member of the League for Programming Freedom -- mail email@hidden
Project lead for Gimp Print -- http://gimp-print.sourceforge.net
"Linux doesn't dictate how I work, I dictate how Linux works."
--Eric Crampton
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