Ricoh VT3500, Service Manual

Page: 153 / 330

[Moire]
When the CCD scans an image made up of regular lines such as a resolution
chart, the output image may have another regular pattern over the regular
lines. This is called "moire".
The above illustration shows one of the moire mechanism. In this case, the
pixel density of the CCD is the same as the density of the regular lines of the
original. However, the regular lines are slightly out of step with the CCD pixel
elements due to some magnification error when they were scanned. As a
result, each CCD pixel has a different value (as shown in the above figure).
Since the length of a CCD pixel is very short, the waveform from the CCD
output looks like the cross lines in the figure. The moire pattern appears
when prints are made from this signal. The moire pattern typically appears
when the CCD pixel density is a multiple of the regular lines density.
CCD
Original
Image
1.7V
CCD
Output
Data
Data for
One CCD
Element
Waveform
1 December 1993
2-117