2 Systems Architecture, Fifth Edition Chapter Goals Describe common concepts of text and image...

2Systems Architecture, Fifth Edition

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 (continued)

• 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


Basic Print and Display Concepts

• Share many features– Character representation methods

– Measurement systems

– Methods of generating color


Matrix-Oriented Image Composition

• We’ll take a look at:– Display surfaces

– Fonts

– Color

– Numeric pixel content


Display Surface

• Commonly used: paper, cathode ray tubes, flat panel displays

• Divided into rows and columns similar to a large matrix– Each cell (pixel) represents one simple component of an

image

• Resolution– Number of pixels displayed per linear measurement unit

– Stated in dots per inch (dpi)


Fonts

• Collection of characters of similar style and appearance

• Usually measured in points (one seventy-second of an inch), which refers to height of characters


Color

• RGB (additive colors)– Generates color by mixing red, green, and blue

• CMY (subtractive colors)– Generates color using cyan (absence of red),

magenta (absence of green), and yellow (absence of blue)

• CMYK color– Four-dye scheme using a separate black dye (K)


Numeric Pixel Content

• Bitmap– Stored set of numeric pixel descriptions

• Monochrome display– Displays one of two colors

– Requires only one bit per pixel

• Grayscale display– Displays black, white, and shades of gray


Numeric Pixel Content

• Palette– A table of colors

– Number of bits used to represent each pixel determines table size

• Dithering– Generates color approximations by placing small

dots of different colors in an interlocking pattern

– Half-toning (grayscale dithering)


Image Storage Requirements

• Depends on number of bits that represent each pixel and on image height and width in pixels

• Can be reduced with bitmap compression– Graphics Interchange Format (GIF)

– Joint Photographic Experts Group (JPEG)

– Moving Pictures Experts Group (MPEG)

• All above compression methods are lossy, resulting in some loss of image quality


Image Description Languages (IDL)

• Address drawbacks of bitmaps (large size and device dependence) by storing images compactly

• Can represent image components in several ways– Embedded fonts

– Vectors, curves, and shapes

– Embedded bitmaps


Adobe PostScript and Portable Document Format

PostScript PDF

• Used in printing and publishing and as graphic file interchange format and embedded printer technology

• Lacks features needed to generate and manage documents as an integrated whole

• Ability to distribute compressed documents with complete authorial control over exact format of the printed and displayed document, regardless of end user’s specific computer, OS, or printer


Video Display

• Character-oriented video display terminals (VDTs)

• Video controllers• Video monitors


Character-Oriented VDTs

• Integrated keyboard and video display surface• VDTs

– Most common form of video display in 1970s and much of 1980s (until PCs)

• Network computers or thin clients– New class of VDT in 1990s

– Limited processing capabilities


Video Controller

• Enables communication between computer system and monitor– Accepts commands and data transmitted via a bus

from the CPU

– Generates TV-style analog video signal, which is transmitted to the monitor

• Refresh cycle and refresh rate; video RAM; dual porting; graphics accelerators


A video controller contains RAM, a microprocessor, and embedded software.


Video Monitors

• Separate from keyboards• Common types

– Cathode ray tubes (CRTs)

– Liquid crystal displays (LCDs)

– Plasma displays


CRT

• Enclosed vacuum tube; electron beam is focused toward front surface of the tube, which is coated in phosphor

• Technology relatively old; has disadvantages– Physical size and weight

– Power consumption


LCD• Contains matrix of liquid crystals sandwiched

between two polarizing filter panels• Active and passive matrix displays• Manufactured with thin film transistor (TFT)

technology• Compared with CRTs

– Less contrast– Reduced size, weight, and power consumption– Higher cost


How an LCD works


Plasma Displays• Combine elements of CRT and LCD technology• Flat panel, active matrix devices• Actively generate colored light near surface of the

display; good brightness and viewing• Require more power than LCDs, less than CRTs• Shortcomings

– Limited operational lifetime– Larger pixel size reduces comparative image quality

when viewed from short distances


Plasma displays have no backlight and no color filters; each pixel contains a gas that emits ultraviolet light when electricity is applied.


Printers

Impact (dot matrix) • Slow, noisy• Relatively poor-quality output• Inexpensive

Inkjet • Relatively slow• Excellent-quality output

Laser • Relatively fast• Excellent-quality output


Inkjet Printers

• Most common printing technology• Prints with liquid ink placed directly onto paper• Uses mechanical movement or heat to force ink

out of nozzle• Paper is drawn past moving print head• Resolution is up to 600 dpi


An inkjet printer has disposable print cartridges that contain ink reservoirs, a matrix of ink nozzles, and electrical wiring and contact points.


Printer Communication

• Impact printers– ASCII or Unicode characters

• Inkjet and laser printers– Use pixels as fundamental output unit

– Have relatively large buffers

• IDLs are commonly used to improve printer performance


Laser printers operate with an electrical charge and the attraction of ink to that electrical charge.


Plotters

• Printers that generate line drawings on wide sheets or rolls of paper

• Use inkjet technology• Ideal for blueprints and other engineering

drawings• Also called large format printers


Manual Input Devices

Keyboards • For entering text and commands

Pointing devices • For pointing and selecting buttons or menu items

• For drawing

• For moving the position of cursor

Input pads • For many of same functions as mice

• Also used for signature pads and touch screens


Keyboards

• Translate keystrokes directly into electrical signals• Generate bit stream outputs (scan code) with a

keyboard controller• Can connect to computer in various ways

(e.g., PS/2, USB, wireless)


Pointing Devices

• Mouse• Trackball• Joystick• Input pads (e.g., digitizer tablet)

– Infrared detector

– Photosensor

– Pressure-sensitive pad


Optical Input Devices

• Detect light reflected off a printed surface or object into a photosensor

• Categories– Mark and pattern sensors

– Image capture devices


Mark Sensors and Bar-Code Scanners

• Mark sensor– Scans for light or dark marks at specific locations

on a page (e.g., standardized multiple-choice test)

• Bar code scanner– Detects specific patterns of vertical bars of varying

thickness and spacing

– Typically used to track large numbers of inventory items


Advanced scanning technology can now read two-dimensional bar codes.


Optical Scanners

• Generate bitmap representations of printed images• Bright white light shines on the page; reflected

light is detected by an array of photosensors• Optical character recognition (OCR) devices

– Combine optical scanning technology with intelligent interpretation of bitmap content


Digital Cameras

• Employ optical scanning technology to capture single or still images and store them as raw compressed bitmaps


Portable Data Capture Devices

• Combine a keyboard, mark or bar-code scanner, and wireless communications to a wired base station or computer system

• Provide rapid data capture (e.g., warehouse inventory control, package routing and tracking)


Audio I/O Devices

• Sound: an analog waveform that can be sampled and stored as digital data

• Various mathematical transformations convert complex sounds to a single numeric representation

• Sampling and playback rely on analog-to-digital converters (ADC) and digital-to-analog converters (DAC)

• Monophonic versus polyphonic


Purposes of Sound Generation and Recognition

• General-purpose sound output (e.g., warnings)• General-purpose sound input (e.g., digital

recording for voice email messages)• Voice command input• Speech recognition• Speech generation


Speech Recognition

• Conceptually simple, but complicated by speaker variability, phoneme transitions and combinations, and real-time processing

• Most current systems are speaker dependent• Digital signal processor (DSP)

– Specialized to process continuous streams of audio or graphical data

– Commonly embedded in audio and video hardware


Speech Generation

• Audio response unit– Generates spoken messages based on textual input

(e.g., automated call routing)

• Speech synthesis– Stores individual phonemes within the system

• General-purpose audio hardware (sound card, multimedia controller)


General-Purpose Audio Hardware

• Typically packaged as an expansion card that connects to the system bus of a workstation

• Sound cards include an ADC, DAC, low-power amplifier, and connectors (jacks) for microphone, speaker, or headphone

• Musical Instrument Digital Interface (MIDI)– Compact storage format


Summary

• Concepts, technology, and hardware used in communication between people and computers– Print and display concepts

– Video display devices

– Printers

– Manual input devices

– Optical input devices

– Audio I/O devices

2 Systems Architecture, Fifth Edition Chapter Goals Describe common concepts of text and image...

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