file:///C|/Documents%20and%20Settings/Miz%20B/My%20D...0UGTA/Nuvera%209.0%20UGTA_FINAL/English/psg_iq10.htm8/13/2008 2:37:15 PM
Removing Moiré Patterns from
Images (when scanning or copying)
The following excerpt is taken from
Real World Scanning and
Halftones
by Glenn Fleishman, David Blatner, and Steve Roth:
Moiré patterns occur when scanning copying an original that is
comprised of a halftone. Moiré is a form of digital artifact that
occurs when two regular patterns intersect to form a new
pattern. Because the new pattern is always more coarse that
the two original patterns, the appearance will change as a
function of screen frequency and angle. Typically, the finer of
the two originals patterns are the easier it is to see the Moiré.
Lower frequency halftone screens are less prone to visible
Moiré.
Suggestions for removing moiré patterns:
Examples
Figure 1:
Figure 1: Result of two distinct patterns superimposed
Figure 2:
Figure 2: Patterns with distinct screen angle and LPI frequency
superimposed to form moiré pattern.
"Moiré ("mwah-RAY") patterns are caused by our eyes'
perception of straight lines and repeating patterns. Anytime you
overlay a bunch of straight lines or grids on top of each other,
you have the opportunity for moiré patterns. One grid, all by its
lonesome, never has a problem with these patterns. It's when
you have two or more overlaid on each other that the wires in
your perceptual system get crossed, and these little gremlins
start to appear."
Moiré can occur while viewing scanned halftones on a monitor
screen, because the monitor has a certain screen frequency,
which may or may not be in alignment with the screen frequency
and angle of the original image.
●
From Copy or Scan Services, select the Image quality
tab.
●
If your image contains a
halftone
, make sure you are
NOT using Text Mode. If legibility of the the text is
important, and good reproduction of any pictures is
also needed, consider using
Mixed Text & Halftones
as the original type.
●
Decrease the Sharpen control slightly. See
Adjusting
Sharpness
.
●
Rotate the original slightly on the Document Glass.
●
Wherever possible, scan/copy continuous tone images
(for example, photographs) only. If there is no
continuous tone original available, scan/copy the
halftoned image as a last resort.
●
When submitting a print job, you may need to select a
different halftone.
●
Scan/Copy at the highest possible resolution capable
by the system.
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If you have programmed and run a job, and
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proceed to do job programming pertinent to your job.
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