> EltonK
Yes, it's true that moire' patterns are the result of linescreen patterns
(and the screen angle in multi-color printing), however BANDING may be
a result of certain linescreen patterns for entirely different reasons.
And yes, you can also get banding as a result of having too few intensity
levels. It is important that your file resolution and imagesetter
resolution and linescreen resolution all be selected to preserve all 256
shades of gray. It would be better, certainly, if we were able to use
more than 256 shades -- and the time is not so far off, I understand the
next version of Photoshop will be a 16-bit program -- however, 256 shades
seems to be adequate (albeit, just barely) for most work.
David
>
> At 06:28 AM 2/24/98 -0800, Beakman wrote:
> >> I, too have been working with Island Imaging. Scott Blaylock is
> >> definitely a great guy to work with. He REALLY wants to make this work.
> >> However, I am using Fokos' method for digital negs, rather than
> >> Burkholder's. So far, they have been experiencing banding problems with
> >> this output and are still trying to work out a fix. I'll post again to
> >> the list as soon as I get a good negative from them. I think it's only
> >> a matter of time.
> >>
> >> Kerik
> >
> >
> >I am assuming that the banding you are experiencing is primarily in the
> >highlights. The key here is to:
> >
> >a) tweak the compensation curve to match your particular paper/coating
> >method/developer combination
> >
> >and
> >
> >b) get the exposure of the digital negative correct. You may think "but
> >they're just black dots", but this is not true. The negative acts like a
> >hybrid analog/digital negative and it is important that the density of
> >the negative be correct in order to mate correctly with the
> >characteristic curve of your paper.
> >
> >Because you are trying to match a an irregular curve moving a little in one
> >direction or antother along the curve will create a mismatch, and hence
> >banding.
> >
> >To help you visualize this, consider a graph of the characteristic curve
> >of your paper. Next, cut a piece of cardboard to match this curve. Mark the
> >10% point on the cardboard curve. Now move align the point you just
> >marked with the 15% point on the graph -- this represents making a
> >digital negative too dense (for a correctly exposed negative the 10% mark
> >of both the cardboard and the graphe would line up). With the 10% and
> >15% marks aligned you will note a curve mismatch -- you won't be able to
> >get both curves to match along their entire lengths. The points where
> >the two curves diverge can lead to banding.
> >
> >c) Banding can sometimes be caused by the type of line screen used --
> >round dot, for exapmple has banding near 50%, elliptical dot in other
> >areas. The differently shaped dots were all developed to help this
> >problem. There are even some special linescreen patterns which change
> >shape depending on the density.
> >
> >d) Print so that your 1% dot prints paper white. Do not have any 0% dot
> >areas in your negative.
> >
> >e) In my image file I make the very lightest, non-pure-white tone have at
> >least a 7% density (this is before the platinum compensation curve is
> >applied).
> >
> >Good luck!
> >
> >David
> >
> >
> Exhibiting fine-art and editorial photography
> Cycloid Fathom Gallery
> Elton N. Kaufmann, Chairman
> P. O. Box 8129
> Downers Grove, Illinois 60517-8129
> USA
> cycloid@cycloid-fathom.com
> http://www.cycloid-fathom.com/gallery/
> ftp.cycloid-fathom.com/group/uploads/
>
>