Chapter 6, Output

Discovering Computers 2004

Modified 29 Mar 04 2353 hrs.

Topics

Output is data sent to an output device.
Digital or analog
Think industrial, as well as office, computers.
Output: control signals, text, audio, graphics, animation, video, 3-dimensional virtual reality
Output device: a device to which output is sent.
Think industrial, as well as office
Industrial: can be a positioning controller on a numerically controlled machine.
Display devices: audio, visual, tactile
Display devices
Soft copy (volatile, or non-volatile and not human-readable), Hard copy (non-volatile, human-readable)
Superior technical discussion by IBM: http://www.pc.ibm.com/ww/healthycomputing/index.html 
Monochrome: Mono = One, Chromos = Color.
Single color display.  One of the following colors is often used: white, amber, green, or sometimes blue.
Higher resolution than a display using multiple colors.
Gray scaling: the number of discrete levels of intensity control.  Discrete intensity levels to generate shades of gray.  Three shades of gray (off, dim, and bright) are common.
Multi-Color Display
Perceived color is produced by displaying a triad of colored dots.
RGB: Red Green Blue
CYM: Cyan Yellow Magenta
Applications
Additive system: RGB is used for emissive displays, such as projective monitors, theater lighting.
Subtractive system: CYM is used in paints, and inks for printed pictures.
Monitor Size and Number
Display size is measured diagonally between opposite corners of the display device.
 
Viewable size is measured diagonally between corners of the viewing area.
15, 17, 19, 21, 22 inch monitors available
13-inch and 15-inch monitors are adequate for working with a single document full-screen with minimum number of rows of tool-bars displayed.
17-inch monitor 
This is adequate for working with a single document and simultaneously displaying several rows of tool bars.  For users of MS Word and Corel WordPerfect, I recommend at least a 17-inch monitor.
This size permits using larger magnification of text when using a word processor.  This is really nice as you get older, even when you have glasses with a current prescription.
This is the minimum size for comfortable interactive video game use.
Monitors larger than 17-inches:
Makes it easier to work with multiple documents simultaneously.
Text recommends monitors larger than 19 inches for graphic arts use.
Multiple monitors.  
This is really great if you are creating multimedia work.
This is great if you are doing a lot of copy and paste between documents, such as a book or newspaper editor might do.
You need to have a video card that supports two monitors, or two video cards.
Under Windows 98, one monitor is designated as the primary monitor which displays the desktop.
Under UNIX with X-WINDOWS, multiple monitors can as a single wide monitor.
Location of Point in an Image
Continuous Source Image: 
X-Y Coordinates, color, intensity.
Used when the image source is continuous, such as a picture, or a pair of voltage inputs.
Line Sampled Continuous Source Image
Line number, displacement on line, color, intensity.
Usually associated with CRT displays, such as television.
Video camera.
Usually specified as a timing from the home position rather than as line number and displacement.
Discrete Source Image: Pixel = Picture Element.  
X-Y Cell Coordinates, color, intensity.
Used when the image source is a discrete set of points.
This is the smallest addressable location in an electronic image.
Digital camera, image stored in a computer.
This is related to the amount of memory needed to support the display device.
CRT monitor: 
CRT Basics
Common computer monitor and television display device.
Emissive display: Light is emitted by the display device.  Image is projected rather than reflected.
Good tutorial at http://www.pcguide.com/ref/crt/const.htm 
Excellent technical discussion for laymen at http://repairfaq.org/REPAIR/F_monfaq.html 
viewable size, diagonal measurement
Mounting brackets are positioned at the front edge of the CRT glass envelope, as well as along the neck.  Usually, these are hidden from view by plastic.  This reduces the viewable area.
The tube size informs design engineers of the approximate physical size of the tube.  You are not getting cheated.
shape: curved outer face increases chance of sunlight reflecting into your eyes.
phosphors
color
particle size
persistence, refresh requirement
persistence is the time required for the radiated light to decrease to 10 % of its initial intensity after turning the electron beam off.
You need to use a higher refresh rate with a low persistence phosphor if you want to prevent flicker. 
Screen savers were implemented to prevent phosphor burn-in. http://www.pcguide.com/ref/crt/power.htm 
cathode
focusing and deflection: magnetic, electrostatic
Magnetic focusing is done with coils external to the neck.
Electrostatic deflection is done with two pairs of parallel plates inside the neck.
Degaussing: The purpose of degaussing is *not* to demagnetize the metal, but to create a magnetization that compensates for the earth's magnetic field. The *sum* of the two fields must be near zero! Degaussing coils create a strong alternating magnetic field that gradually decays to zero. The effect is that the present earth magnetic field is "frozen" into the magnetic shielding and the field inside the shielding will be (almost) zero. Non-zero field will cause color purity errors. Now you will understand why a CRT must be degaussed again after it has been moved relative to the earth's magnetic field. This will also explain why expensive computer monitors on a swivel pedestal have a manual degaussing button, you must press it every time after you have rotated the monitor.  Sam Goldwasser, "Color CRTs, Shadowmasks, Magnetic Fields, and Degauss", Phillips NV, AnaTek, Netherlands
http://www.anatekcorp.com/smask.htm , 07 OCT 2001
Distortion control is easier with long-necked tubes and curved screens.  The issue is beam focusing.   It is more difficult to control near the edges, particularly on flatter screens. You probably would not want to see images displayed near the edge.
Physically reducing the proportional variation in distance between the location of the focusing control and the phosphor side of the glass envelope reduces the need for controlling distortion through sophisticated beam control.  This is done by long necks and curvature of the glass envelope.
Businesses like short necks and flat screens.  Short necked tubes take up less space on a desk.  Flat screens look more like a sheet of paper.  More sophisticated electronics are needed to compensate for larger deflection angles and variations in proportional distance. 
Degaussing:  Do this if you change the orientation of the monitor, have a nearby lightning strike, or there is some change in the local magnetic field (like placing loudspeakers near the monitor, or other unshielded equipment).
CRTs are manufactured for different latitude regions on earth.  
If you move to South America, Africa, or Australia, you may need a different monitor.  
An LCD display does not have this problem.
Beam Control
vector mode: beam controlled to produce high quality line drawings similar to an etch-a-sketch, used for engineering
raster scan: 
beam scanned across screen nearly horizontally (exaggeraged greatly in the drawing below).
beam turned off when repositioned for next line
interlacing: 
One beam is painted (pretend it is the blue beam) top to bottom.
Another beam is spaced between the first set (pretend it is the red beam) top to bottom.
used on TVs, not compatible with computer monitors
can get TV Tuner cards that will capture TV signal and convert it.
refresh rate, vertical frequency, or vertical scan rate: Hertz (Hz) = cycles per second
Put your hand in front of the monitor and wave it back and forth.  Notice the stroboscopic effect.
60 Hz; for TV, 30 Hz interlaced with 30 Hz
Higher refresh rates permit use of lower persistence phosphors without appearance of flicker.  This is good for computer displays.
70 - 75 Hz; becoming common.
85 Hz; made by Silicon Graphics Inc.
Beating with ambient lighting is not a significant factor in choosing refresh rate.
Power Consumption, Energy Saver 
high voltage safety 
http://www.pcguide.com/ref/crt/powerCover-c.html
electromagnetic radiation health hazards http://www.pcguide.com/ref/crt/powerEmissions-c.html 

purple line shows effect of turning monitor electron guns off.
Energy Use Reduction
Monitors designed to reduce use of electricity sometimes have an "Energy Star" label.
If you do not move your mouse or use your keyboard for a predetermined amount of time, 
an Energy Star monitor can turn off the electron guns of the CRT.  This greatly reduces power consumption.
a computer can go into standby mode.  Some PC standby modes will stop the motor that spins the hard disk drive.
The time lapse before energy saving actions are taken is usually selectable through the control panel.
VDU (Video Display Unit) EMR (electromagnetic radiation)
Center for Office Technology report: http://www.cot.org/basics.htm#anchor585750 23 FEB 2002
The overwhelming majority of the research that has been conducted indicates that there is no link between exposure to VDT EMF and increased risk of miscarriage or other adverse birth effects.
Epidemiological studies have generally failed to show a difference in pregnancy outcomes between women working and not working with VDUs during pregnancy.
You are not going to get cancer from sitting in front of your monitor.  If this is a concern of yours, talk to me after class and I can arrange for you to see research data on the topic.
If this is a real concern of yours, you should also not watch TV.  [ Remember telling your kids, or being told, to not sit so close to the TV? ]
Electromagnetic radiation decays rapidly with distance, but does not completely cease to exist.
CRT Monochrome, gray scaling
Uniform coating of phosphor, not in dots.  
Can get much sharper displays.
Can draw true continuous lines, which is not possible on a color monitor.
Data entry monitors: 
character generator
80 columns (same as punched cards) x 23 lines
Later models used included shapes to permit limited graphics capability
Eventually, some raster scan models used dots to form characters, and permit graphics
less expensive than general purpose monitors
Measurement instrument monitors:
Character generator usually not included, except on high priced models.
Phosphor persistence, refresh rate are important, and are chosen for the application.
Control of electron beam focus, scaling, motion, and start time are important.
Color (RGB = red, blue, green)
triad of color phosphors and pixel concept
Pixel = Picture Element
Resolution as pixels per (row, column) (horizontal, vertical) 
640 x 480, 800 x 600, 960 x 720, 1024 x 768, 1152 x 864, 1280 x 960, 1280 x 1024, 1600 x 1200, 2000 x 1024, 2048 x 1536
The concept of a triad and a pixel are independent.  For an excellent discussion, see http://www.repairfaq.org/REPAIR/F_crtfaq.html#CRTFAQ_012 
Dot pitch is a measure of the physical distance between triads, measured between dots of the same color, and is the limiting physical factor in resolution.
Pixel refers to the logical format of the display, and a pixel is a single addressable location in an image.
Dot pitch: distance between adjacent blue dots, shortest distance between adjacent dots or bars of the same color.  Example: 0.19 mm; text recommends using a display with a dot pitch of 0.29 mm or less. Merely stating dot pitch as the distance between adjacent pixels is not a complete specification.
Dot pitch of some typical television monitors: http://www.repairfaq.org/REPAIR/F_crtfaq.html#CRTFAQ_011
* 13" GE - .60 mm.
* 19" Samsung - .75 mm.
* 25" RCA - .9 mm.
Beam alignment to dots: 3 ways. Graphical comparison: http://firingsquad.gamers.com/guides/hiwmonitors/images/sharpse-s.jpg 
shadow mask: a thin sheet with a tiny circular hole for each triad http://firingsquad.gamers.com/guides/hiwmonitors/page6.asp 
aperture grill: thousands of vertical tiny filament wires across the screen 
slot mask: a thin sheet with a tiny vertical rectangular hole for each pixel http://firingsquad.gamers.com/guides/hiwmonitors/page7.asp 
Recycling: Lead problem, groundwater contamination.
Flat-panel display
LCD: liquid crystal display
Liquid crystal forms an ordered structure like a crystal along one dimension, but acts like a liquid in the other two. Science, 21 November 2003
requires only about a third of the room as a CRT for similar display size.
much lower power consumption than a CRT, good for battery powered computer systems.
viewing angle not as great as for a CRT.
Technical tutorial on LCD displays: Bruck Scott, http://margo.student.utwente.nl/el/misc/lcd_faq.htm 
Another good tutorial on LCD displays: PC Tech Guide, http://www.pctechguide.com/07panels.htm 
Liquid Crystal Displays (LCDs) are categorized as non-emissive display devices, in that respect, they do not produce any form of light like a Cathode Ray Tube (CRT).  LCDs either pass or block light that is reflected from an external light source or provided by a back or side lighting system.
Backlighting consists of having a light source on the back side of the LCD display to increase the contrast between text and background.
passive matrix
Passive matrix displays utilize DIRECT ADDRESSING; the charge is applied directly from the drivers to the pixel element.
Passive matrix displays use less power than active matrix displays.
High-Performance Addressing (HPA) on new models increases the image quality.
active matrix or TFT (thin film technology): separate transistor for each color pixel
Active matrix displays utilize INDIRECT ADDRESSING; the charge is "filtered" through a switch before reaching the pixel element.
Active matrix displays are easier to view than passive matrix displays without being directly in front of the display.
Color displays: There are two layouts for pixels on TFT displays. 
The most common for computer applications is the STRIPE layout. A stripe layout has repeating stripes of red, green, and blue columns across the display. 
For projection LCD modules, a triad pixel layout is used. A triad layout has the three color sub-pixels in a triangle shape.
Digital versus Analog Connection
LCD monitors use a digital signal.  Traditional computer monitor output signal is analog, which means conversion is necessary.  Some newer video cards provide a digital output.
Analog connection is via a 15-pin VGA connector.
Digital connection is via a 24-pin DVI-D connector.
Viewing Size
A 15-inch flat panel display has about the same viewing area as a 17-inch CRT.
Orientation
Some LCD monitors can be easily rotated 90 degrees to make viewing long documents easier.
Gas plasma
large display; layer of gas (neon)
Expensive.
CRT vs plasma display: http://store.hamptonimage.com/crtvsplasdis.html 23 FEB 2002
No loss of focus with position on the display.
Uniform intensity with position on the display.
Not affected by changes in the local magnetic field.  Therefore, you do not need to make different models for the Northern and Southern hemispheres.  This is good for vehicles: ships, planes, space craft.
Field Emission Display (FED)
Multimedia Hardware
Multimedia Personal Computer
PC97: 120 MHz Pentium, 16 MB RAM, USB Port
For multimedia preparation: 700 MHz Pentium III, 256 MB RAM.
Sound Card
audio digitizer
wave table synthesizer
mixer
CD and DVD ROM Drives
PC Camera
Speakers
Produce sound by physical vibration of the transmission medium (usually air).
Big speakers require more power than the usual sound card can produce. Beware!
Reflex-coil speakers use magnets.  Do not put your magnetic disks near them.
Lower frequencies require larger speakers to transmit directional sound.
Display Device
Televisions and Data Projectors
NTSC converter: to connect TV to computer
NTSC: National Television System Committee
Television Standards: From http://www.tenlab.com/worldtv.htm 
Developed in the U.S., it was the world's first color TV system. Broadcast started in 1954. 
Basic Parameters NTSC M
line/field 525/60
horizontal frequency 15.734 kHz
vertical frequency 60 Hz
color subcarrier freq. 3.579545 MHz
video bandwidth 4.2 MHz
audio carrier 4.5 MHz (FM)
Video Capture Card
Video capture software
Digital Video Interleave (DVI): Intel proprietary video compression
Scanners, Digital Cameras, PhotoCDs
Color scanner
Digital camera
Small disk
PC Card
Internal memory
Photo CD
Laser Disk and Laser Disk Players
Video card = graphics card = video adapter
Digital Display Working Group (DDWG) is developing the Digital Video Interface (DVI) which provides connections to CRT and LCD monitors.
Video Electronics Standards Association (VESA).
SVGA = super video graphics array: 800 x 600, to 1600 x 1200
Color representation: bit depth, color depth.  One word per primary color, 3 primary colors per pixel.  The color resolution depends on the word size.  24 bits per pixel yields 8 bits per primary color.  8 bits provides 256 intensity levels for a particular primary color.
Poynton's Color FAQ: Includes hexadecimal codes for colors. http://www.inforamp.net/~poynton/notes/colour_and_gamma/ColorFAQ.html 
video RAM = RAM in monitor or on video card for display use, separate from main memory.
Reduces computer main memory devoted to display functions.
Increases responsiveness to image changes.
Monitor ergonomics
Display height compared to eye height: Improved by putting the system unit somewhere else.  The tower model was a big contribution to reducing neck strain in viewing monitors.  Before the tower model, monitors were often placed on top of the system unit (as in our lab).
Swivel base
Reduced monitor neck length.  On desks, this allows you to move the monitor further away.
Increased resolution.
Front panel controls.  Degaussing circuits.
HDTV = High definition television. Two approaches.
8-VSB Selected in USA over COFDM, JAN 2001: http://63.249.17.65/hdtv/cofdmvs8vsb.html 
HDTV is scheduled to be broadcast by all TV stations in the USA by 2006.
Tutorial: http://www.calcote.com/hdtv.htm
16:9 aspect ratio for HDTV versus 4:3 aspect ratio for NTSC.
1080 to 1125 lines for HDTV versus 525 lines for NTSC.
Tutorial: http://www.ee.washington.edu/conselec/CE/kuhn/hdtv/95x5.htm 
Goal: Increase the percentage of the field of vision filled by an image.
8-level vestigial sideband (VSB) technique: The 8-level signal is derived from a 4-level AM VSB and then trellis coding is used to turn the 4-level signals into 8-level signals. Additionally, the input data is modified by a pseudo-random scrambling sequence which flattens the overall spectrum. Cable transmission is by a 16-level VSB technique without trellis coding.
HDTV Links: http://www.bgsu.edu/departments/tcom/hdtv.html 
8-VSB
8-level Vestigial Sideband.
Vestigial Sideband (VSB)
Type of Amplitude Modulation (AM)
Compromise between Double Sideband (DSB) and Single Sideband (SSB) AM modulation
Gradual cutoff filter rather than sharp cutoff used
Transmit most of the upper sideband
Transmit partial corresponding part of the suppressed lower sideband
B. P. Lathi, Modern Digital and Analog Communication Systems, Chapter 4, Holt, Rinehart and Winston (1983)
Adaptive equalizer.
Less affected by impulse noise from household appliances.
Lower cost of construction and operation.
Efficient use of spectrum.
Multipath ghosting problem in big cities.
Used in USA.
Broadcasters are using an 8-VSB, 19.5 Mbps of data http://videoessentials.com/glossary.htm 
Cable companies have developed a 16-VSB system that operates in the standard 6 MHz TV channel bandwidth.
COFDM 
Coded Orthogonal Frequency Division Multiplex.
Better for mobile use, better for dynamic multipath, including reflection off moving objects such as vehicles or rain.
Developed in USA by Bell Labs.
Sinclair Broadcast Group comparison testing in June 1998.
Used in Europe.
8-VSB comparison test with COFDM report: http://63.249.17.65/hdtv/mstvtestsum.html 
Digital versus Analog for entertainment broadcast.
The benefits of digital transmission are (1) no distortion of image due to transmission, (2) signal compression, (3) error detection and correction coding, (4) encryption, and (5) message switching.  
Digital signal compression includes techniques of encoding (which replaces duplication with redundancy counts and permits exact reconstruction) and approximation (which discards noise and unusable extra resolution, by using Fourier or Wavelet transformation)  which reduces the amount of information transmitted.  
Error detection and correction are not critically important in entertainment broadcast, but can be very important when including data and other communication services along with the cable transmission service.  
Encryption is very important to the entertainment broadcast industry to enforce pay-per-view and channel subscription sales.  While it is possible to scramble and reconstruct one analog signal using another as a reference, maintaining an exact replica of the reference signal at the receiver end is not as easy.  
Message storage (buffering) and switching is easier to implement for digital messages than analog messages.
Analog techniques exist for increasing resolution, signal compression, and multiplexing.  
All non-synthesized audio and video signals begin as analog signals.  Digitizing (sampling) will always discard information.  An increase in audio and video resolution begins with an increase in analog resolution.  For raster-scan video, you must increase the scanning resolution before you can encode it.
Signals can be compressed by band shifting (translation) to higher frequencies.  Filters are used to discard noise and can also discard unusable extra data (outside a design pass-band).
Frequency division multiplexing is a technique for encoding multiple signals on separate carrier frequencies into a common pass-band.
Analog techniques could have been used to achieve high definition television for wide screen and increased resolution.  The digital approach to HDTV brings the robust properties of digital compression techniques, encryption, and message switching that are important to the entertainment broadcast industry.
As we continue to develop technology for the future, we must be careful to revisit first principles rather than to assume that a modification of current technology will always produce the best results for a given application.  Digital is great, but do not always assume it is best.
Printers
Hard copy (non-volatile human-readable) versus soft copy (volatile, or non-volatile that is not human-readable).
Speed: pages per minute, lines per minute, characters per second.
Resolution: dots per inch (dpi)
Letter quality
Near letter quality
Orientation: portrait, landscape
Paper supply:
sheet: best for home and office use
continuous: tractor feed (holes on the side) or pressure feed
Tractor feed is best for multipart paper, forms, and very high speed printing
Pressure feed is inexpensive, and adequate for unattended logging
Impact: dot matrix, line or band, shuttle matrix
Required for multipart paper
Line or band printer is very high speed, low quality.  Adequate for billing and internal records.
IBM 6400 i2s line matrix printer: 2000 lpm in draft mode, 1500 lpm in DP mode. http://www.printers.ibm.com/internet/wwsites.nsf/vwwebpublished/6400data_ww 29 March 2004
IBM Infoprint 3000 Advanced Function Printing System Model ED1 / ED2: 224 impressions per minute (ipm). http://www.printers.ibm.com/internet/wwsites.nsf/vwwebpublished/3000data_ww 29 March 2004
Non-impact: ink-jet, laser, thermal, electrostatic
Ink carrier particle size is the limiting factor for printer resolution.
Ink-jet
Hardware is cheap.
Ink cartridges are expensive per printed page. 
$35 for inkjet cartridge
2 reams of 500 sheets
Cost per page: $35/1000 sheets = $0.035/sheet
You can get ink-jet cartridges cheaper by shopping over Internet. Example: Carrotink at http://www.carrotink.com 
Laser: 
works similar to a Xerox copier. (High end Xerox copiers can accept digital input of documents.) 
Resolution: dots per inch (dpi), horizontal and vertical.  600 - 2400 dpi available.
75 dpi is OK for draft text quality.
150 dpi is OK for office correspondence.
300 dpi is good for text reports.
600 - 800 dpi is needed for special symbols used by engineers and scientists.
900 - 1200 dpi is needed for continuous tone graphics.  Higher resolution produces better quality.
1200 dpi is the resolution professional printers used in 1994.
2400 dpi is available in office supply stores.
Higher resolution printing requires ink with smaller carrier particles, which increases ink price.
Higher resolution requires more memory.
Can get color laser printers (expensive).
Hardware is expensive.
Printer memory size important.  
For text with simple graphics, 4 MB minimum, 8 MB better.  This should be adequate for a business office serving a few people.
Full page bit mapped graphics need 16 MB or more memory.
High speed printers need more memory.
Black ink cartridges are cheap per printed page. The ink is called "toner".
$100 for HP2100 laser toner cartridge
1 case of paper (10 reams of 500 sheets)
Cost per page: $100/5000 sheets = $0.02/sheet
Image control: PDL = Page Description Language
PCL = Printer Control Language (Hewlett-Packard)
Post Script (ps) (important in UNIX environment)  Can get a Post Script cartridge for laser printer.
printer servers
Reduces the number of printers in an office
When accessible via Internet, these can provide output for remote computers (including mobile and handheld computers)
Special purpose: photographic, label printers
Picture ID Card printers
Plotters
flat bed, drum
pen, electrostatic
Quality engineering drawings are done with a flat bed pen plotter.  These can be quite large.
Large format printer: Ink jet technology.
Audio output: loud speakers, headset
Do not attach large speakers to your computer audio output.  If you want entertainment quality speakers for a large room, get speakers with an external amplifier or built-in amplifier.  Otherwise, you will destroy your audio interface electronics.
Pay attention to the impedance specifications, given in Ohms.
FAX = facsimile machine.
Used to send and receive images of documents over the telephone.
A computer with a fax modem can encode a text file for transmission as a fax document.  It is received on the other end as a fax document, not as a text-editable document.
Multifunction device (MFD): combined scanner and printer, allowing use as FAX and copier
Data projectors
LCD = liquid crystal display
DLP = digital light processing projector.  Uses micromirrors to focus reflected light.
Terminals
dumb: requires a host computer
intelligent (programmable)
special purpose ~ point of sale or ATM
Force-Feedback Joysticks and Wheels
Flight simulators and trainers
Games
Accessibility options: 
keyboard: sticky control, shift, alt; ignore brief repeated key strokes; sounds for hitting caps lock, num lock, and scroll lock
sound: visual warning when computer makes warning sounds; captions for speech and sounds used by programs
display contrast: high contrast
general: auto reset to standard configuration after selected idle time, notify when feature is being turned off, alternative serial input device port
Braille printer