Digital BW, The Print

It seems that it would be better to try your test at 180, 360, 540 and
720 for Epson printers.

-Message: 1
   Date: Sat, 18 Oct 2003 13:08:41 -0000

   From: "J Michael Sullivan" <michael@...>
Subject: Re: Optimum resolution for inkjets

Do the following test:

take a sharply-focussed, highly-detailed, but *UNSHARPENED* (this is
important) 
image of yours at 600 dpi (or more accurately 600 "spi": samples per
inch) and print 
it at 8"x10" @ 1440dpi
then downsample it to 400 spi and print that
then downsample it to 200 spi and print that

and tell me if you see any difference. (I just did this myself, btw).
Most people can 
readily see a difference with the 200 spi image, but can't see any
significant 
difference between 400 and 600 (at least not at 1440 dpi output).

All things being equal, epson uses a custom stochastic dithering
algorithm that is 
likely based on "something" in the neighborhood of 360dpi as its base
from which to 
derive the dither. Send any more than that to the printer and the data
is certainly 
DOWNSAMPLED by the printer. The test above more or less proves this.
Stick with 
something in the neighborhood of 360 spi and you can't go wrong.

It's easy to prove, with test prints, that Epson desktop models resample to
exactly 720ppi, and large format models resample to 360ppi. Here's a good
test:

	http://www.pbase.com/image/22493977

This has alternating black and white lines at 360 lines per inch (assuming
you leave the resolution set for 720ppi). If you print this on a desktop
machine, you should see gray, because it will correctly render both the
black and the white. If you change the resolution to 1440ppi and print it,
one half will come out white and the other half will come out black. If you
set the resolution to some oddball value, like 1420ppi, you'll see black and
white aliasing bands.

Some drivers have an option for "smooting edges". I believe this does some
filtering on the image to avoid aliasing, so turn this off.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@...