Re: Colorsync-users Digest, Vol 5, Issue 209 - AM/FM screens
Re: Colorsync-users Digest, Vol 5, Issue 209 - AM/FM screens
- Subject: Re: Colorsync-users Digest, Vol 5, Issue 209 - AM/FM screens
- From: Lee Badham <email@hidden>
- Date: Mon, 16 Jun 2008 09:38:00 +0100
Hi List,
FM screening has a higher dot gain than conventional screens. This is
because of there are many smaller dots, each which can spread (more
circumference), rather than a lesser number larger dots.
So what the printer is doing is closing the ink ducts and reducing
the solid ink density to reduce the dot gain back to the same as that
of the AM screened plates. That surely will also affect the solid ink
colours. Maybe because it won't affect the grey balance, the G7
people think this is ok. The solid colours are not affected by the
screening technology used, because there is no screen.
Lee Badham
FOGRA Certified ISO12647-2 Examiner
Bodoni Systems Ltd
+44 (0)1895 825776
On 16 Jun 2008, at 00:09, Roger Breton wrote:
Brian,
As amazing as it sounds, that's the sad truth.
I've personnally witnessed this very phenomenon on press.
Start with AM plates, run a number of sheets, adjust SID. Then
stop. Change
over to FM plates, start again and observe how all ink keys must be
closed
down, by a sizeable amount, in order to obtain the same color.
I mentioned this puzzling fact once on the G7 Expert list and was
told that
this was a very well known fact in the industry. I was even given a
link to
a GATF comparative study where this behavior is documented. I
followed the
link through but I shied at purchasing the article in question :
Stochastic Printing, Printability, and Runnability Compared to
Conventional
Screens [2004]
Author: John Lind
Subtitle: A Research and Technology Report
Stochastic printing appeals to many printers these days, with some
reports
estimating that half of all printers have experimented with the
technology.
Some of the advantages touted for stochastic include greater
rendition of
detail, less sensitivity to changes in register, less sensitivity
to increased
inking, no moiré patterns, less ink consumption, and greater color
gamut
volume.
This Research and Technology Report is the result of a study
conducted for the
2004 Tech Alert Conference that sought to validate such claims by
printers and
vendors. Specifically this study examines ink consumption,
documents the tonal
calibration process, and looks for differences in blanket piling
between
conventional screens and one stochastic algorithm for coated and
uncoated
paper. The choice of test form used in the study allowed the
comparison of the
color gamut volumes for 133 lpi, 175 lpi, and 25-micron
stochastic. Use the
conditions, properties, and print run data reported here to help you
investigate stochastic printing or benchmark conventional screening
conditions.
Contents: Introduction • Stochastic Past and Present • Stochastic
Pros and
Cons • Sources of Stochastic Technology • Methods and Materials •
The Test
Form • The Calibration Process • Ink Consumption and Blanket
Interactions •
Color Gamut Considerations • The Economics of Using Less Ink •
Summary and
Conclusions • Acknowledgments • References • Appendix A. Project
Protocol •
Appendix B. Calibration Data for Coated Paper • Appendix C.
Calibration Data
for SCA Uncoated Paper • Appendix D. Results for the Adjusted
Curves and the
Final Print Runs, Coated Paper • Appendix E. Results of the
Adjusted SCA Print
Runs
Given your comments, I think I'll reconsider...
Best regards,
Roger Breton
Regarding Roger's comments...
Why would switching from AM to FM result in an ink savings?
You're putting down the same dot area, and that would result in
approximately the same amount of ink being put on the paper.
The only thing that changes is the formation of the tonal
information:
a clump of machine spots vs. a pseudo-random distribution of the same
machine spots.
If you were to calculate the area of paper covered by ink per cell in
an AM halftone and compare that the area covered by ink per cell with
an FM screen, they should be the same, or very close, otherwise the
image would be different.
I am eager to hear the explanation.
Best wishes,
Brian P. Lawler
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