Input and Output Technology in Computing
Explore concepts of text and image representation, printer technology, and input devices. Learn about display devices, pixel composition, image quality, and color representation in print and video.
Input and Output Technology in Computing
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Presentation Transcript
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
Resolution • 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
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
Display restrictions • Size of color palette (number of possible colors)http://www.lynda.com/hex.html • Resolution of the screendemo storage requirements (excel)..\..\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 • http://www.will-harris.com/type-fun.htm
Basic Concepts of Print and Display 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
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
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
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.
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
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.
