Cis Technology - Colortrac M25e Service Manual

10

CIS Technology

A Contact Image Sensor (CIS) is an integrated module that comprises an illumination system, an
optical system and a light-sensing system - all within a single compact component.
Cross-section of a CIS scanner sensor.
The illumination is provided by Light Emitting Diodes
(LED's) shining down a light guide, which in turn
directs the light onto the document. There are three
LED's (Red, Green, and Blue) which strobe rapidly,
thereby providing the colour content in the scan. Note
that there are no colour filters in the optical or light-
sensing system. The colour gamut of a CIS scanner
is therefore determined by the spectrum of each of
the LED's, rather than by colour filters as is the case
with CCDs. Because colour filter technology is more developed than LED spectrum technology, a
CIS scanner will not provide as wide a colour gamut as a CCD scanner.
However, rapidly strobed LED's require no warm-up period. Therefore, a CIS scanner can be
switched on and used immediately. Furthermore, LED's are very stable which means that a CIS
scanner does not require frequent re-calibration.
The light-sensing system is the silicon surface which is
divided up into (e.g. 5000) discrete square cells, the
size of each being a fraction of an inch depending upon
the required scanning resolution (a 600 dpi scanner will
use a CIS whose cells are 1/600" across). The optical
system is a rod lens array that directs light from the
document surface onto the silicon surface. Such an
optical system is 1:1; i.e. there is no reduction or
enlargement; and this results in a scanner offering the
best performance in terms of resolving power and
geometric accuracy.
M Series Service Manual
M Series SingleSensor CIS
Page 11 of 129
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