| FAQ's
Welcome to iSAFE Solutions FAQ on scanner basics. The Scanner
Resource Center is your one stop source for any kind of information
regarding scanners.
Q. What are the different types of scanners available?
A. There are three types of scanners:
- 1. Drum scanner
- 2. Flat-bed scanner
- 3. Handheld scanner
Q. What is a drum scanner?
A. A drum scanner is an optical input device that mounts original
images on a revolving cylinder for scanning.
Q. What is a flat-bed scanner?
A. Any scanner that incorporates a flat transparent plate, on which
original images are placed for scanning, is a flat-bed scanner. The
scanning process is linear rather than rotational.
Q. What is a hand-held scanner?
A. A hand-held scanner is a portable, low-cost scanner which is
plugged directly into the computer's printer port, as opposed to the
SCSI port. To scan a document, the scanner is scrolled over the
document by hand.
Q. What is scanning?
A. Scanning an image is like a copier copying an image. The major
difference is that the output of scanning is an electronic file
which can be edited by a software and stored in a disk.
Q. How does a scanner work?
A. The scanner uses a light source, typically a cold cathode lamp to
illuminate the scanned object. The light is then reflected off the
object and into Charged Coupled Device (CCD). The Charged Coupled
Device collects the information, and through a series of electronic
devices converts the analog signal into a series of digital signals
which can then be read and processed by a computer.
Q. What can you do with a scanner?
A.
- Optical Character Recognition (OCR) - You can convert
text-based document images into text that can be edited by a
word-processing software.
- Enrich your presentations and documents by adding images.
- Convert hard-copy images or documents into a fax format for faxing
or for record purposes. 4 Add scanned images to your e-mail to
enrich your content.
Scanner Jargon Resolution Pixels DPI LPI PPI Preview Image Type
Bit Depth Optical Resolution Maximum Resolution (Interpolated
Resolution) Interface Image Size File Formats Compression Lossy
compression Lossless compression
Q. Resolution
A. The number of pixels displayed per unit of printed length to
represent a bitmap image. Usually, resolution is measured as dots
per inch (dpi) or pixels per inch (ppi).
Q. Pixels
A. The smallest element that can be displayed on a screen or
printer, in other words it's the smallest picture element unit in an
image.
Q. DPI
A. An acronym for dots per inch, a measurement of resolution. Higher
the DPI higher is the scanned image resolution.
Q. LPI (Lines Per Inch)
A. A term used in printing as a measurement of the frequency of
lines on a screen (usually ranging from 55-200). LPI refers to the
frequency of the horizontal and vertical lines.
Q. PPI (Pixels Per Inch)
A. A measurement of the amount of scanned information. The finer the
optics of the scanner the higher the scan resolution. PPI is
equivalent to DPI.
Q. Preview
A. An operation that gets a rough image of a document for setting
parameters and image analysis.
Q. Image Type
A. According to the contents of your documents, the image can
basically be divided into three types.
- Line Art The Line Art image type is used for documents
containing lines, text and detailed drawings. If OCR
(Optical Character Recognition) software is used for
document management, the Line Art image type should be
selected and the resolution be at 300 dpi or higher. When
the original is a negative film, this type is unavailable.
- Grayscale A grayscale image is composed of pixels with 8
bits (256-shades) and contains only white, black and
intermediate shades of gray.
- Color Image The Color Image type is used for images with
continuous tones and with lots of gray shades or colors.
Color photos contain more information than any other type of
images, but they also occupy much more disk space and system
memory.
Q. Bit depth
A Also known as pixel depth, it defines the number of bits used to
represent each pixel in an image. It also determines how many colors
every pixel in a bitmap can have. In other words, the depth of
information recorded during the scanning process is limited by the
chosen bit depth.
Q. Optical Resolution
A This refers to the number readings taken from an original image
within a given distance, as opposed to the subsequent increase in
resolution (but not detail) created by software interpolation.
Q. Maximum Resolution (Interpolated Resolution)
A. The process of increasing the resolution of an image, with the
help of a software, by the addition of new pixels throughout the
image, the colors of which are based on neighbouring pixels. For
example, to create another dot between adjacent dots of Red values
100 and 108, the new dot can be assumed to have red value 104, so
the transmission is 100, 104, 108. The same is done for Blue and
Green, and the image will look smooth and larger.
Q. Interface
A. Interface is the type of connection used. The four most common
types are
- Parallel (uses 25pin connector, same port that a
printer would use) - USB (short for Universal Serial Bus, common on
newer computer systems) - SCSI (Small Computer System Interface,
requires SCSI controller, very fast) - Firewire (Extremely fast IEEE
1394 connection, requires firewire card)
Q. Image Size
A. A large image size will lower the system performance of your
computer dramatically. The file size is affected by the selected
area, file format, scaling ratio, resolution and the image type. The
following table presents the detailed information (file compression
is excluded):
Image Type Description 1-bit images Black and White Line Art
8-bit images Black and White or Color Image, 256 gray levels or 256
colors 24-bit images Color Image, Millions of Colors 32-bit images
Color Image, Billions of Colors
Q. File Formats
A. File format determines the structure of information to be saved
in a file. Refer to the following table to obtain better
performance. File Format File Extension Advantages TIFF .tif
- Efficient file size
- Can save color separations EPS .eps, .epsf
- Can save duotone information Can save clipping path
- Can save color separations PCX .pcx Used by most
software applications PICT .pict, .pct
- Has Compact file size BMP .bmp
- Used by most software Targa .tga Can save alpha
channel JPEG .jpg, .jpeg
- Has the best compression ratio
Q. Compression
A. Encoding the bits of information in an image file so that it
takes up less space when stored. Compression results in little or no
distortion. File compression falls into two general categories:
- Lossy compression and
- Lossless compression
Q. Lossy compression
A. Lossy compression assumes that some of the data in the image file
is unnecessary and can be eliminated without affecting the quality
of the image scanned. Typically this type of compression has ratios
between 10:1 and 100:1.
The most popular lossy compression option is JPEG. JPEG stands
for the Joint Photographic Experts Group, which developed the
compression standard. JPEG compression ratio is selectable in the
host software and ranges from 2:1 up to 40:1.
Q. Lossless compression
A. Lossless compression stores image data in a file without deleting
information, that is, no loss of image details, color or output
quality. If the 2:1 compression ratio is enough, lossless
compression can to be considered.
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