Contex XD2490 Service Manual page 39

AdaptiveThresholding
Advanced 2-D Adaptive Thresholding estimates the back-
ground gray level in a window area around each pixel. The dif-
ference between the actual pixel value and the background is
then compared to the adaptive settings to determine if a pixel
is thresholded as a black or a white pixel
Additive Colors:
The additive primary colors are red, green and blue. These
additive primaries represent the three main components of
white light. Used individually or together, these three colors of
light can be mixed to create nearly all colors. When these three
primary colors are mixed in equal parts they produce white.
Additive color is used in scanners and computer displays.
ADL+ Error Diffusion Halftoning
Image Processing that supports visibility of graytones in
printed output by adding toned shades of gray in regions
between black and white. Carried out as a segment of Dual
2D-Adaptive enhancement processing in copy modes.
ALE - Accuracy Lens Enhancement
Accuracy Lens Enhancement (ALE) is an electronic correction
of spherical errors in CCD based camera- scanning systems.
When looking at pixels across the range of a camera, the pixels
tend to be more elliptical at the outside edges of the lens and
more round in the middle of the lens. This anomaly is known
as a spherical lens error and can introduce inaccuracies in the
scanning system that can vary quite substantially between
different points along the scan line. Most manufactures typi-
cally state a +-0.1% accuracy of the scanner between the two
outermost end-points of the scan line. However, when measur-
ing between two points that do not fall across the entire scan
line, it is not unusual to see variations of up to +- 0.5% or even
higher. This is naturally unacceptable in demanding environ-
ments and markets such as GIS, which need a stable and well-
defined maximum error of 0.1% or less.
ALE solves this problem by a process to electronically correct
the spherical errors in the scanner and maintain a stable maxi-
mum error across any two points of less than 0.05% ± 1 pixel.
ATAC
Automatic Thickness Adjustment Control - A special technol-
ogy that allows the scanner pressure platen to be raised to
accommodate thick originals and then lowered - both actions
performed by pressing a key from the operators panel. Sensors
in the platen detect when perfect pressure is applied to the the
original and automatically stop the downwards motion of the
platen so it rests on the original with an optimal grip.
Appendix - C --- Scanner Terms
Bitmap:
An image format made from a matrix of individual pixels.
.bmp.
Bitmapped Image:
A bitmapped image is a computer file representing a line-art
image that was scanned with a scanner. Refers to the pattern
(map) of bits that are either black or white.
Black Level
The Black Level is a setting in scan programs used to change
dark graytone colors to true black. For example, if one is copy-
ing a brochure with a mixture of text and pictures, the text will
often be digitized to a color that we may see as black but really
is a dark graytone. When the printer digests this graytone data,
it will print the original's text with a halftone pattern, meaning
scattered dots instead of solid black. By increasing the Black
Level value, one can get the text to be copied in real black and
it will therefore appear clearer.
Black Point Adjustment
An adjustment made that will determine the amount of shadow
detail in an image. It is considered proper to set the black point
so that the darkest part of an image will only just have zero
detail.
Blueprint
A process of photographic printing used mainly for copying
architectural and mechanical drawings; produces blue lines on
a white/bluish background.
Blur
The averaging of pixel elements.
Brightness Adjustment
An adjustment on a scanner that allows the user to compensate
for a light or dark original.
Calibration
Adjusting a device so that it performs in accordance with an
established standard. Scanner calibration is minimizing color
deviation between scanned ANSI IT8 reference color patches
and the known color reference values. Generally, Calibra-
tion is the process of setting a device to known color condi-
tions - stabilizing the device to a known and quantifiable state.
Calibration is commonly done with devices that change color
frequently, such as monitors (phosphors lose brightness over
time), scanners (light changes) and printers (proofers and other
digital printing devices can change output when colorant or
paper stock is changed).
C-1