Moiré patterns are a natural interference phenomena that appear in all
color CRT displays. Moiré patterns appear as ripples, waves, and wisps of
intensity variations that are superimposed on the screen image. They are most
noticeable on high resolution displays that have finely focused beams.
Moiré patterns are a double-edged sword because you need to worry about
them whether or not you see them. If you don't see them, it's possible that
your display is producing a fuzzy image, which is the case in most improperly
adjusted or poor quality displays. If you do see them, they're annoying.
A Moiré pattern arises because the pixels that are generated by the video
board cannot be perfectly aligned with the phosphor dots or stripes on the
screen. For some pixels the CRT beam hits the screen phosphors dead center,
and produces a bright pixel, and for others it hits off-center and produces a
dimmer pixel. The Moiré pattern is actually a map of their alignment over
the screen. For color televisions, a Moiré pattern can arise from
the color subcarrier.
Moiré patterns are not a defect in the monitor, but rather result from
a practical limitation in display technology. In order to completely eliminate
Moiré patterns, the dot or stripe pitch on the monitor would have to be
significantly smaller than the size of a pixel, which is generally not possible.
For example: to be completely free of Moiré, a 17 inch diagonal display
with a resolution of 1024 x 768 would require a dot or stripe pitch of 0.12 mm,
which is a factor of 2 smaller than anything currently available.
There are several ways to minimize or eliminate Moiré patterns:
- If your display includes a Moiré Reduction Control, find the best setting,
write it down, and then temporarily turn-off Moiré Reduction. Next try the
steps below and see which method produces the best image. Some Moiré
Reduction Controls are not effective and may introduce unwanted
- Slightly defocus the image using the monitor's Focus Control.
Be careful not to over do-it, so that you don't reduce sharpness.
Alternatively raise the intensity using the Contrast Control,
which also increases the beam size. If the screen is now too bright for your
eyes, attach an anti-glare screen, which will cut down light transmission.
- Change the image size or shift resolutions. Moiré patterns are most
noticeable when the ripples are separated by a few millimeters. By increasing or
decreasing the image size or the pixel size, you can literally wind the
Moiré pattern up or down, thereby making it less noticeable.
- Don't use a dim Window Background. The dimmer the Window Background color,
the more noticeable the Moiré patterns will be throughout the entire window
background because the beam size is smaller at low intensities.
- Try to eliminate dithering, which makes the Moiré patterns worse.
Avoid 16 color Windows modes, which generally have a lot of dithering.
Dithering occurs much less frequently in 256 color modes and is generally
absent in 32K color modes and above.
- DisplayMate includes a special set of patterns that enhance the visibility of
the Moiré patterns, which makes it a lot easier to see what they are and to
see what you are doing, and then shows you how to reduce or eliminate them.
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