screen printing > Separations
Ellipse Vrs Dot shape benefit "example attached"
drdot:
@Yorkie and anyone else who is deeply interested, Adobe Press has an excellent book on Postscript Halftoning written by Peter Fink way back in 1992 or so. I remember poring over it trying to understand halftone arrays, moire periodicity, super cells, irrational angles, and so on. It is still one of my core reference books on digital imaging along with Ulrich's Digital Halftoning.
Here is info on Fink's Book:
Postscript Screening: Adobe Accurate Screens
explains in detail all the issues and specifically covers Adobe
Accurate Screens -- Adobes' own screening technology. Peter Fink
is an expert on the subject of halftone screens as they relate to
color issues.
Author: Peter Fink
Publisher: Adobe Press, Oct 1992.
ISBN 0-672-48544-3
yorkie:
The things which interest me, go beyond "accurate screening".
"in"-accurate screening was a byproduct of the limitation of the computers of pre-1992. It has been 19 years since 1992. Computers back in the day were 30 mhz, not dual or quad 3 ghz.
It is my belief, that screen printing on textiles needs its own book.
Please go back and review the not proportional ratio screen i posted. Is that in the book?
drdot:
--- Quote from: yorkie on May 06, 2011, 12:40:28 AM ---It is my belief, that screen printing on textiles needs its own book.
Please go back and review the not proportional ratio screen i posted. Is that in the book?
--- End quote ---
I think you're missing the point. Both of the references I cited are foundational material to build your skill set. As an example, the post on moire and "strobe effect" would be enlightening as what you describe is, indeed, a form of moire. The discussion in Fink's book on accurate screens, etc, has more to do with moire issues than on processing speed of the computers. Have you read it?
Your interest in a "not proportional ratio screen" is nothing more than a hybrid screening option. Mike Ware of Waatsch Technologies has developed a wonderful hybrid Stochastic/AM screening model available in their Soft RIP product. It is ideal for screen and flexo printers. It's his approach to dealing with highlight and shadow issues inherent with AM halftones. It is his attempt to solve the same problem you are proposing to solve with your idea.
Postscript offers almost infinite possibilities on how to create a halftone model depending on the printing method, ink characteristics and behavior, and substrate. What you outlined is one possible solution.
Structurally it has some issues, but that also is not the point. Experiment. See what you get. That's how discoveries are made.
Any halftone approach is a balance between visual surface texturing (noise), accurate tone translation, and stable consistency of production. The model you are proposing is still an ordered array model (AM) and any ordered array model will have challenges for screen printers.
For us, the ideal halftone model would be an intelligent mix of FM and AM halftoning based on the rate of change of surface detail over any defined area. What this means is that the algorithm would analyze the image and where the detail was low (eg sky, large areas of flat color) it would place an AM or ordered array dot. Where there is rapidly changing detail (hair, fabric texture, regular patterns like picket fence or screen door mesh) you would get an FM dot of a predetermined dot size.
This approach is processing intensive, but offers the possibilities to balance extremely fine detail with precise tone control. It's a way of losing the visual dot as part of the printed image.
squeezee:
Have you seen Mike's latest wheeze?
Imagine that you can print from 10-90% quite happily but lose detail after that. Mike has got a trick where the dots are postscript down to 10% and remain at that size so that you can print them. To get a 9% dot he removes some of the dots and progressively to 1%. It doesn't look perfect but it's a really good approximation. It's a sort of stochastic approach to AM dots.
Clark:
--- Quote from: squeezee on May 06, 2011, 11:09:31 AM ---Have you seen Mike's latest wheeze?
Imagine that you can print from 10-90% quite happily but lose detail after that. Mike has got a trick where the dots are postscript down to 10% and remain at that size so that you can print them. To get a 9% dot he removes some of the dots and progressively to 1%. It doesn't look perfect but it's a really good approximation. It's a sort of stochastic approach to AM dots.
--- End quote ---
I think my old multi light exposure table used to do this on its own.....lol
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