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Scanner. Computer Peripherals First Semester Second year Faculty of computers and information. Scanner Types. Flatbed scanners (desktop scanners) The most versatile and commonly used scanners. Sheet-fed scanners

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Computer Peripherals

First Semester

Second year

Faculty of computers and information

scanner types
Scanner Types
  • Flatbed scanners (desktop scanners)
    • The most versatile and commonly used scanners.
  • Sheet-fed scanners
    • similar to flatbed scanners except the document is moved and the scan head is immobile.
  • Handheld scanners
    • similar to flatbed scanner, but rely on the user to move them instead of a motorized belt.
    • Less quality.
  • Drum scanners
    • are used by the publishing industry to capture incredibly detailed images. They use a technology called a photomultiplier tube (PMT). In PMT, the document to be scanned is mounted on a glass cylinder. At the center of the cylinder is a sensor that splits light bounced from the document into three beams. Each beam is sent through a color filter into a photomultiplier tube where the light is changed into an electrical signal.
  • Charge-coupled device (CCD) array
  • Mirrors (2 or 3)
  • Scan head
  • Glass plate
  • Lamp
  • Lens
  • Cover
  • Filters
  • Stepper motor
  • Stabilizer bar
  • Belt
  • Power supply
  • Interface port (s)
  • Control circuitry
charge coupled device ccd array
Charge-coupled device (CCD) array
  • CCD is a collection of tiny light-sensitivediodes, which convert photons (light) into electrons (electrical charge).
  • These diodes are calledphotosites. In a nutshell, each photosite is sensitive to light -- the brighter the light that hits a single photosite, the greater the electrical charge that will accumulate at that site.
  • The image of the document that you scan reaches the CCD array through a series of mirrors, filters and lenses.
the scanning process
The Scanning Process
  • The document is placed on theglass plateand thecoveris closed (white or black) background that the scanner software can use as a reference point for determining the size of the document being scanned.
  • A fluorescentlamp is used to illuminate the document.
the scanning process8
The Scanning Process
  • The scan head (mirrors, lens, filter and CCD array) is moved slowly across the document by abeltthat is attached to a stepper motor. The scan head is attached to astabilizerbarto ensure that there is no wobble or deviation in thepass.
the scanning process9
The Scanning Process
  • The image of the document is reflected by an angledmirrorto another mirror (to focus the image it reflects onto a smaller surface).
  • The last mirror reflects the image onto alens. The lens focuses the image through afilteron the CCD array.
  • The filter and lens arrangement vary based on the scanner.
  • Three passscanning
    • Each pass uses a different color filter (red, green or blue) between the lens and CCD array.
  • Single pass scanning
    • The lens splits the image into three smaller versions of the original. Each smaller version passes through a color filter (either red, green or blue) onto a discrete section of the CCD array.
the scanning process11
The Scanning Process
  • Contact image sensor (CIS)
  • CIS replaces the CCD array, mirrors, filters, lamp and lens with rows of red, green and blue light emitting diodes (LEDs).
  • When the image is scanned, the LEDs combine to provide white light. The illuminated image is then captured by the row of sensors.
  • cheaper, lighter and thinner
  • less quality and resolution
resolution and interpolation
Resolution and Interpolation
  • Resolution
    • x-direction sampling rate (number of sensors in a single row (
    • y-direction sampling rate(precision of the stepper motor)
  • Sharpness
    • depends on the quality of the lens and the brightness of the light source.
  • Interpolation
    • a process that the scanning software uses to increase the resolution of an image.
    • It does this by creating extra pixels in between the ones actually scanned by the CCD array (300x300 to 600x300)
  • Bit depth (color depth)
    • The number of colors that the scanner is capable of reproducing
image transfer
Image Transfer
  • Parallel
  • (Universal Serial Bus (USB
  • (Small Computer System Interface (SCSI
  • FireWire
image transfer14
Image Transfer
  • TWAIN is known as Technology Without An Interesting Name!
  • TWAIN , most scanners speak a common language
  • The TWAIN driver acts as an interpreter between any application that supports the TWAIN standard and the scanner.
  • OCR software allows you to scan in words from a document and convert them into computer-based text.
That’s it!

Thanks for your attention