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

Re: photopolymer

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. (2450/4=ppi)

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)

Ender100@aol.com wrote:
Oops I meant to say more in the 300-400 ppi range.

In a message dated 5/5/07 6:46:26 PM, jon@terabear.com writes:

Hi Mark,

CopyGraphics had been doing them for me at 1800 dpi (an Agfa standard apparently).

The new company I've been using has a SciTex imagesetter rendering at 2540 dpi. It was either that or 1270 dpi...

This is not to say the screen pattern is literally 2540 dots per inch, rather, the SciTex imagesetter simply uses that resolution to create the stochastic pattern. Under a lupe the pattern of the 2540 screen actually looks coarser than the pattern of the screen done at 1800. SciTex stochastic patterns looks less like film grain than what Peter did for me originally with the 1800 dpi screen off their Agfa imagesetter...

Best Wishes,
Mark Nelson

Precision Digital Negatives - The System <http://www.precisiondigitalnegatives.com/>
PDNPrint Forum at Yahoo Groups <http://groups.yahoo.com/group/PDNPrint/>
www.MarkINelsonPhoto.com <http://www.markinelsonphoto.com/>

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