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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 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.
