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Scanner Types - PowerPoint PPT Presentation

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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

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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.

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  • 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

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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.

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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.

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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.

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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.

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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

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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

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Image Transfer

  • Parallel

  • (Universal Serial Bus (USB

  • (Small Computer System Interface (SCSI

  • FireWire

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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.

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That’s it!

Thanks for your attention