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Chapter 7. Input/Output Technology. Chapter goals. Describe common concepts of text and image representation and display including digital representation of grayscale and color, bitmaps, and image compression techniques

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Chapter 7 l.jpg

Chapter 7

Input/Output Technology

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Chapter goals

  • Describe common concepts of text and image representation and display including digital representation of grayscale and color, bitmaps, and image compression techniques

  • Describe the characteristics and implementation technology of video display devices

  • List and describe the three predominant manual input technologies

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Chapter goals

  • Understand printer characteristics and technology

  • Describe various types of optical input devices including mark sensors, bar code readers, scanners, and digital cameras

  • Identify the characteristics of audio I/O devices, and explain how they operate

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Print vs. video display

  • Print has a thousand year history

  • Techniques have developed for the design and representation of characters

  • Most of these techniques have been transported to video display

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Matrix oriented image composition

  • Representing text starts with the display surface

    • Paper, video, television, computer screens

  • Display can be subdivided into rows and columns (a table or matrix)

  • Each cell in matrix is a pixel

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  • Smallest element of graphical representation of text or image

  • Print – can be empty or contain one or more inks or dyes

  • Video – empty or display light of varying color and intensity

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Pixels and Paper

  • Traditionally pixel size corresponds to smallest drop of ink that can accurately placed on page

  • This is called a point, i.e. 12 pt, 14 pt

  • Printer’s standard is 72 pts per inch

  • This measurement is now standard, although modern printing can apply ink in smaller quantities

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Pixels and computer display

  • Pixel size for modern video display is typically between 0.2 and 0.3 millimeters

  • Number of pixels on a surface depends on the size of the surface (height and width) and size of the pixels

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  • Important factor in the quality of image

  • For print resolution is expressed as dots per inch (dpi)

  • Laser printers - 600 dpi

  • Commercial printing - 1200 dpi

  • Screen resolution varies from 640x480 to 800x600

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Poor resolution & computers

  • Computer uses binary information to store graphical images

  • For each pixel, binary information must describe the appearance of the pixel

  • Binary information is a representation of the color of each pixel

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Color in video vs. print

  • Human eye interprets different light frequencies as different colors

  • Video – color is generated directly by the display device

  • Print – color is the light frequency reflected by the page

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Color cont.

  • Display – three primary colors are Red Green blue RGB. These three are mixed together to produce all colors.

  • Print uses subtractive colors – cyan (absence of red) magenta (absence of green) and yellow (absence of blue) plus black, or CMYK

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Representing colors

  • Colors are represented in computers using 0s and 1s

  • Each pixel is assigned a fixed amount of bits to represent its color, i.e. 24 bits

  • Collection of colors that can be represented in the available bits is called the color palette

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Display restrictions

  • Size of color palette (number of possible colors)

  • Resolution of the screendemo storage requirements (excel)..\..\Desktop\newmonitor.xls

  • Image representation can be improved through image compression formats (.GIF, .JPEG, .MPEG)

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  • Collection of characters in a similar style is called a font

  • Fonts have evolved over the centuries


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Basic Concepts of Print and Display

Vector – a line segment that has a specific angle and length with respect to a point of origin

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Video Display

  • Character-Oriented Video Display Terminals:

    • Commonly used during 1970s and 1980s.

  • Terminal – consist of an integrated keyboard and television screen.

  • Used today primarily in systems such as retail checkout counters and factory floor environments.

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Video Display

Thin Client – a hybrid device with a mix of VDT and microcomputer characteristics. They execute applications within an operating environment such as Java, a Web browser, or Windows Terminal Services

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Video Display

Video Controller – accepts the commands and data transmitted via a bus from the CPU and generates a TV-style analog video signal which is transmitted to the monitor

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Video Display

Monitor Types:

  • Cathode Ray Tube (CRT)

  • Liquid Crystal Display (LCD)

  • Plasma Displays

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Printer Types:

  • Impact – dot matix

    • Nearly obsolete expect for printing multiple forms

  • Laser

  • Inkjet

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  • The print head of an ink-jet printer consists of an ink cartridge, a set of ink chambers and a set of ink nozzles

  • Each ink nozzle can print a single pixel and nozzles are arranged in short vertical rows similar to those of a dot matrix printer

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  • Operates differently from other types of printers

  • No print head or ink ribbon is used

  • An internal image of the entire page is stored in an internal buffer as a bit map.

  • Once filled, the buffer contents are sent to the print driver for generation

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Manual Input Devices

Input Devices:

  • Keyboards

  • Pointing Devices

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Manual Input Devices

Keyboard Input:

  • Keyboard devices translate keystrokes directly into electrical signals.

  • A keyboard controller is used to generate bit stream outputs.

  • The controller generates a bit stream output according to an internal program or lookup table.

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Manual Input Devices

Pointing Devices:

  • Mouse

  • Trackball

  • Joystick

  • Digitizer Tablet

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Manual Input Devices

Pointing Devices:

Translates the spatial position of a pointer, stylus, or other selection device into numeric values within a system of two-dimensional coordinates

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Manual Input Devices

Pointing Devices:

  • Mouse – a pointing device that is moved on a flat surface such as a table, desk or rubber pad.

  • Trackball – a mouse with the roller ball on the top. The roller ball is moved by the fingertips, thumb or palm of the hand.

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Manual Input Devices

Pointing Devices:

  • Joystick – used as an input device with computer games.

  • Digitizer Tablet – uses a pen, or stylus, and a digitizing tablet. The tablet is sensitive to the placement of the stylus at any point on its surface.

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Optical Input Devices

Mark Sensors and Bar Code Scanners:

  • Mark Sensors – scans for light or dark marks at specific locations on a page

  • The mark sensors uses preprinted bars on the edge of the page to establish reference points

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Optical Input Devices

Optical character recognition (OCR):

  • Combine optical scanning technology with hardware or software interpretation of bit map content

  • The bit mapped representation is searched for patterns corresponding to printed characters

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Audio I/O Devices

Sound generation and recognition can be used in a number of ways

  • General-purpose sound output, such as warnings, status indicators, and music

  • General-purpose sound input, such as digital recording

  • Voice command input

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Audio I/O Devices

Speech recognition:

  • The process of recognizing and appropriately responding to the meaning embedded within human speech.

  • Human speech consists of individual sounds called phonemes.

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Audio I/O Devices

Speech Generation:

  • A device that generates spoken messages based on textual input is called audio response unit

  • Simple audio response units digitally store and play back words or word sequences

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  • Manual input devices include keyboards, mice and other pointing devices

  • A stored set of numeric pixel descriptions is called a bit map

  • Video display terminals consist of an integrated keyboard and television screen

  • Commonly used paper output devices include dot matrix printer, ink-jet printer, laser printers, and plotters

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  • Optical input devices include optical scanners, mark sensors, bar code readers, and optical character recognition devices

  • General-purpose speech recognition systems can be used for command and control, or for the input of large amounts of textual material

  • Sound cards include converters, amplifiers, microphone, speaker and headphone connectors