Re: Dot proofers
Re: Dot proofers
- Subject: Re: Dot proofers
- From: Graeme Gill <email@hidden>
- Date: Mon, 06 Mar 2006 10:27:46 +1100
Mark Rice wrote:
If you have an inkjet device that prints at 600 or 1200 dpi, and you
are attempting to simulate dots that would appear on a 4000 dpi
platesetter, there is no way you will achieve the same dot structure,
or even the same screen angles.
There certainly are ways of representing the dot structure and color
of a screened original on an inkjet printer, and maintaining the
exact screen angles (been there, done that). The result is not crisp
however (using any reasonable DPI inkjet), and there is a trade-off
between sharpness, aliasing between the imagesetter screen and the
inkjet screen, and color precession.
Several years ago I worked with someone who was an excellent postscript
programmer. He designed an algorithm that would feed in screen angles
at 1 degree intervals, and then see what came out of the image setter
(1200 dpi).
Here are some of the input angles and actual achieved output angles:
In Out
1 .8
2 1.7
3 2.5
4 3.3
5 4.2
6 4.9
7 5.7
8 9.3
9 9.9
and so on.
Yes, on some PostScript RIPs, this is the case. Others have better screening
algorithms that don't have these limitations (look up supercell screening).
This has nothing to do with proofing imagesetter originals. The inkjet doesn't
have to have any sort of traditional screening algorithm to reproduce dot originals,
it just has to resample the image (paying attention to Nyquist filtering), before
processing through it's own usual color correction and stochastic screening.
You won't get the crisp screened dots of a proofing process that reproduces the
imagsetter output exactly (eg. chemical or equivalent), but the exact dot structure
is preserved, and the color may well be a closer match.
Graeme Gill.
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