Canon FAX-L1000 - Manual (Page 180)

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FAX-L1000 Chapter 3: Technical Reference
b) Structures
b-1) Contact sensor
The contact sensor is designed to be dust-free, so that dust and other such minute particles
cannot find their way inside the contact sensor housing, to settle on the sensor surface.
The contact sensor consists of an LED array that emits light for scanning, a lens that
distributes light from the LED array uniformly in the horizontal direction, a contact glass
that refracts the light to the document, a rod lens array that receives the light reflected
from the document, and a phototransistor array that receives reflected light.
The LED array of the contact sensor is controlled by the SCNT board.
The phototransistor array consists of 1728 phototransistors (2054 phototransistors for AE)
and 11 driver circuits (13 driver circuits for AE) that amplify the light reception output in
units of 158 phototransistors.
The output from the 13 driver circuits is converted to serial data and sent to the SCNT
board.
b-2) Prescanning
At the start each communication, the prescan function reads in one line of the white sheet
pasted to the document feed section at the top of the contact sensor, stores the contact
sensor output variation correction value into memory, and corrects contact sensor output
for the image then read in.
b-3) Automatic slice level
The SCNT board image processing IC has a built-in ABC (Automatic Background
Control) circuit. This circuit sets the slice level for each line of image data read, so that
gradations can always be reproduced clearly, no matter the background color of the paper.