#MOIRE PATTERNS
4 messages in this thread
How does one avoid moire patterns in process colour screen combinations?
How to avoid Moire patterns in process color separations?
Put simply, one doesn't. I assume you are using Adobe Separator to do the
color separations…if this is the case, then AS is calculating all of the
rotations, etc automatically.
Under normal conditions, the actual "scrrens" of halftone dots are rotated
to achieve the least possible amount of moire. Generally speaking, you get less
of a distracting pattern when there is more of a difference in rotations; but
it all depends on where the dots fall, and how intense the colors are.
Adobe Separator uses the standard screen rotations to achieve its process
colors…but unless you are outputting to a very high-resolution printer (like
the Linotronic L-300), that has been painstakingly calibrated to optimize fine
screens, you'll notice the moire patterns – the larger the dots, the greater
the effect. The L-300's 2450 dpi resolution is really needed here – even the
L-200 produces coarse color seps (it only achieves 1270 dpi).
-Scott Leyes
Scott:
We have an L-300 on order and plan to start doing what we hope will be
"pleasing color" on it. What are you specifically talking about when you say
"painstakingly calibrated"?
Also have you used, or do you suggest using, elliptical dots, or any other dot
pattern besides the default postscript dots??
When I say "painstakingly calibrated", I mea that you need to have the
Linotronic service reps to a precise densitometer testing on your machine when
you get it. I don't know all the details, but the exposure settings on a Lino
can change/degrade over time, due to shipping, etc. Also, there is an
occasional problem here and there with the mirrors, like a spec of dust getting
in the way (whick can cause hairlines to appear in the output). What you should
definitely do is get some test examples from the major programs you plan to
output, along with some "pure" handwritten PostScript code, and out them while
you've got the service reps there… check to see consistency of grays, line
rules, etc.
On another note, I've only used non-round screen dots on the LaserWriter; I
see no reason why they wouldn't work on the Lino, but memory might become a
factor (longer processing too).
-Scott Leyes