Scanner system
The flatbed image scanner captures an electronic image of the document on the glass. The scanner does this
by illuminating the document with LEDs (red, green, and blue) and capturing the image in the image sensor to
create an electronic format of the document. The flatbed scanner consists of three main elements
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CIS scanner. The CIS (contact image sensor) scanner captures an image using the product's optical path.
Red, green, and blue LEDs sequentially illuminate a small strip of the document (often called a raster
line), and the optical system captures each color in a single row of CCD sensors that cover the entire
page width. Because only one color is captured for each line per exposure, the three colors are
recombined electronically to create the full color image. For monochromatic scans or copies, all three
LEDs are illuminated to create a white light for the scan so the raster line can be captured in one
exposure.
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Mechanical carriage drive. The carriage drive moves the CIS scan head along the document length to
create the image. In this product, a small DC motor with an optical encoder creates this motion. The
speed of the carriage drive is proportional to the scan resolution (300 ppi is much faster than 1200 ppi)
and also proportional to the type of scan (color scans are three-times slower than monochromatic
scans). A 1200 ppi color scan moves so slowly that the product may appear to not be working, whereas
a monochromatic copy scan moves at 50 times that speed and will be a little noisy.
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Image processing system (formatter). The formatter processes the scanner data into either a copy or a
scan to the computer. For copies, the image data is sent directly to the product without being
transmitted to the computer. Depending on user selections for the copy settings, the formatter
enhances the scanner data significantly before sending it to the product. Image data is captured at 300
ppi for copies and is user selectable for scans to the computer. Each pixel is represented by 8 bits for
each of the three colors (256 levels for each color), for a total of 24 bits per pixel (24-bit color).
Electrical system
Scanner power-on sequence of events
When the product is turned on, it performs the following tests:
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Wall find. The scan carriage moves slowly to the left while watching an encoder on the carriage motor
to determine when the carriage has found the left side wall or stop. This enables the product to identify
the document origin (position of the original). If the document origin cannot be located, a default
position is used instead.
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Home find. The scan carriage uses the optical scanner to find physical reference features that relate to
the document origin at the left side of the image glass. This process ensures accurate location of the
first document pixels so that the user documents will have an accurate placement of the image on
scans and copies. If the reference feature is not found, it uses a default value.
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Calibration. This test, also known as scanner color calibration, enables the product to identify the black
and white on every pixel in the CIS. Calibration occurs in two major processes: a broad (analog)
adjustment of all pixels to bring them into the target output range, and a pixel-by-pixel adjustment
(digital) to fine tune the actual black and white response. The calibration process occurs under the left
side of flatbed image scanner where there is a special white calibration label.
Calibration is the most important step in creating a high quality image. Calibration problems can include
color inaccuracies, brightness inaccuracies, and vertical streaks through the image. The calibration
process identifies any bad pixels and enables the image formatter to recreate the lost information from
adjacent pixels. Extreme cases of this problem can appear as large vertical streaks or image smears.
Turn the product on or perform a color calibration to force a scanner calibration. Scanner calibration
occurs with each of these events.
ENWW Scanner system 23
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