Descreening filter and resulting image size

[jenlrile]

Hello all-

We're experiencing some strange behavior with the Silverfast descreening filter on a Nikon 4000, Mac, OS10.2, PhotoshopCS, SF AI 6.2.0r6.

When the Descreening filter is selected, the scale% on the frame tab automatically changes to 12.7%. I think this by itself is OK, the scale is adjusted based on the size of the current frame and the currently selected screen lpi. BUT, when we change the screen lpi (using any of the defaults or typing in a custom number), and click OK, the scale doesn't change at all, it's still stuck on 12.7%.

We've also got a Nikon8000, WinXP, Photoshop 7, SF AI 6.2.0r6, and this system does not display this behavior. The scale% changes with the screen lpi listed in the descreen box, which is the behavior I would expect.

Does anyone else see this behavior? Is this a bug or is there something I'm not understanding correctly?

Thanks,
Jenn

[ianders1]

Jenn,

This frustrated me to no end back when I ran into it. It is intentional and has to do with the algorithms used to do the descreening. Here's the explanation from page 190 of the manual:

Limited Enlargement during Descreening
Please be aware that screened artwork has a resolution that is
limited by screen resolution (the number of dots). Therefore,
enlargements are limited during descreening.
The result would automatically be a Moir? pattern or some other
effect! Reduction is no problem.

Just scan as big as you can, then enlarge in PhotoShop as needed.

[jenlrile]

Thanks for the reply, Ian, and the pointer to the appropriate place in the manual. We don't do tons of descreening so I may have overlooked that section initially!

I'll have to do a little more testing here to confirm that this is the cause of the behavior we've been seeing. Initially, I was under the impression that our scale wasn't changing EVER, not just not getting bigger after a certain point. I'll investigate further, RTFM, and post again if we're still experiencing something contrary to what we'd expect.

Thanks!

Jenn