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 Describe the characteristics and implementation technology of video display devices List and describe the three predominant manual input technologies

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

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

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

Pixel 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

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

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

Using pixels to display text

Resolution Important factor in the quality of image For print resolution is expressed as dots per inch (dpi) Laser printers dpi Commercial printing dpi Screen resolution varies from 640x480 to 800x600

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

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

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

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

Color coding examples

Display restrictions Size of color palette (number of possible colors) Resolution of the screen demo storage requirements (excel)..\..\Desktop\newmonitor.xls..\..\Desktop\newmonitor.xls Image representation can be improved through image compression formats (.GIF,.JPEG,.MPEG)

Fonts Collection of characters in a similar style is called a font Fonts have evolved over the centuries fun.htm fun.htm

Sample fonts

Font in different sizes

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

Technology Focus Basic Concepts of Print and Display

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.

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

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

Video Display

Monitor Types: Cathode Ray Tube (CRT) Liquid Crystal Display (LCD) Plasma Displays

Video Display

Printers Printer Types: Impact – dot matix Nearly obsolete expect for printing multiple forms Laser Inkjet

Printers Ink-Jet: 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

Printers Laser: 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

Printers

Manual Input Devices Input Devices: Keyboards Pointing Devices

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.

Manual Input Devices Pointing Devices: Mouse Trackball Joystick Digitizer Tablet

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

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.

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.

Manual Input Devices

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

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

Optical Input Devices

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

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.

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

Summary 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

Summary 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