Re: photopolymer
Erie, 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 www.MarkINelsonPhoto.com In a message dated 5/6/07 12:03:30 AM, erie@shelbyvilledesign.com writes: mark, 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. erie (yes, at one time I did that sort of stuff, and had 2 Lino 330s of my own) ************************************** See what's free at http://www.aol.com.
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