C-5
Appendix - C --- Scanner Terms
Photographic Expert Group, JPEG images feature small file
size and speed, but lower quality than other formats.
Lossless Compression
File compression and subsequent de-compression without any
loss of data.
Lossy Compression
File compression that will compress data to a high degree.
When subsequently un-compressed, data will have been lost.
LZW
Method of lossless compression used with many file formats;
developed by Lempel, Zev and Welch.
Midtones
The most important part of a picture between black (shadows)
and white (highlights).
Negative
A reversed photographic image used to produce a positive
print or a scanned image.
NET - NET Architecture
NET Architecture is a solution for scanning across local net-
works.
What does it do?
• Enables Sharing a scanner on a network.
• Enables scanning to a Designated Scan Folder on
another computer.
NET Architecture allows a a scanner to scan to a client PC in a
single coherent and secure process. The client does not need to
expose or share his local hard disk as the system can be set up
for authorized transfer to the client.
Example of usage - a company that needs to create digital
documents of its drawing archive, can send the drawings to
a service bureau that scans all the documents directly to the
client (company) file server allowing immediate feedback
from the client and prevents digital distribution of confidential
documents outside the client company.
NET Architecture also allows users in a company to use a
scanner, from their own PC workstations although the scanner
is physically placed elsewhere. It only need to be on the same
LAN. In this way a single scanner is “shared” throughout the
company.
Noise
A term used to describe the occurrence of pixels that contain
random colors within an image.
Original
The paper, negative, slide, or film to be scanned.
Palette
The set of colors available for an image.
PICT
A file format for pictures used primarily on the Macintosh.
Pixels Per Inch (ppi)
A measurement of resolution for scanners, where the individu-
al element is a square picture element (pixel).
Pixels
The word pixel is a combination of the two words picture and
element. It is the smallest building block within a scanned
line-art or photographic image. A pixel is the small square
picture element that is filled with a color, black or white. The
value of a pixel depends on the luminance of the area, and is
either a single bit for a black and white image, or multi-bit
for a color or gray-tone image. Pixels come in various sizes
and their size is expressed in terms of resolution. Resolution
is measured in pixels per inch (ppi) or the equivalent dots per
inch (DPI.)
PostScript
A computer language developed by Adobe (R) Systems, Inc.
for printing text, graphics, and scanned images. PostScript (R)
is a vector format that can include scanned bitmapped images.
Raster File
Also called Raster Image or Bitmapped Image. A picture
composed of individual dots (picture elements, pixels) the way
a scanner perceives it. The rows in a high-resolution raster
file typically contain 200 or 300 dots per horizontal inch of
the original drawing, and there are typically 200 or 300 rows
per vertical inch. As each of these dots is defined by location,
and by whether it is on or off, raster images generally result in
large data files.
Resolution of a Scanner
Expressed as DPI (dots per inch) or the equivalent ppi (pixels
per inch). The higher the resolution of a scanner, the smoother
the scanned images.
Resolution
A measure of how many pixels per inch are scanned. Gener-
ally, more pixels per inch means more detail in the picture and
a larger file when saved. Defines the level of detail that can
be captured or shown by a scanner, display, or output device.
For scanners, the resolution is defined by the number of dots
(pixels) per inch (DPI) that can be captured horizontally and
vertically, e.g. 300 DPI equals 90,000 pixels per square inch.
