U of S | Mailing List Archive | alt-photo-process-l | Re: photopolymer

Re: photopolymer

Hi Mark and Erie,

Yeah, this is a bit over my head.  I'm mostly regurgitating what the tech and sales people have told me with regards to the rez of these screens.

I'll send you Peter's info off list Mark.  I'm sure he'd be able to answer your question better than I.


Ender100@aol.com wrote:

Thanks for the note. 

An imagesetter would need a 16 x 16 matrix for 256 tones.  If the imagesetter is set to a native resolution of 1800 dpi, then the file would have to be 112.5 ppi = 1800/16.  If it is set to 2450, it would be 153.125 ppi or lpi = 2450/16.

This is assuming they aren't using some algorythm with a variable dot size.

This is why I was confused with Jon's note regarding a comparison of the different screens:

The basic difference between
the finer one I use and Dan's/Elizabeth's is that the pattern with
theirs is visible to the naked eye. Mine just looks like a dark grey
translucent screen. I'd guestimate theirs to be somewhere on the order
of 150-200 dpi compared to the 1800-2540 dpi screens I've been using.

Jon,  If you have Peter Elsey's current email address, could you send it to me off list?

Best Wishes,
Mark Nelson

Precision Digital Negatives - The System
PDNPrint Forum at Yahoo Groups

In a message dated 5/6/07 12:03:30 AM, erie@shelbyvilledesign.com writes:

IF they're using it properly, i.e. creating a stochastic screen function
and then just telling the imagesetter to output a box so many points
high by so many points wide, filled 80%, then the resolution is device
dependent, and is determined by the RIP, accounting for the matrix size
and rotation. For a 256 gray scale at 0 degrees (typically used), it's a
4x4 matrix, though the rotation, if used affects the matrix size.

There's a good explanation of Postscript halftones in the Postscript
reference books, I think the blue book, though it's been years (~20)
since I've written raw Postscript, so I may be mistaken. The reality is
likely that they're doing it from within a graphics program, and unless
they're intimately familiar with Postscript (and I've only met 3 or 4
people that care enough to be) the likelihood is the graphics software
is outputting a 600 ppi image (Illustrator, in particular is pretty bad
about this, since version 7, as I recall), as opposed to the code to
create a stochastic screen function at the raw imaging unit resolution.

(yes, at one time I did that sort of stuff, and had 2 Lino 330s of my own)

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