LIS508 lecture 6: output devices

Thomas Krichel

2002-10-27

Structure

• Fundamental concepts

• Printers

• Monitors– only at the simplest level– More detailed level not required

Fundamental concepts I

• Pixel– A very small element of a picture– Inside the pixel color and brightness is fixed– All the pixels are created by the computer

• Resolution– Number of pixels per inch– Or total number of pixels, confusion

Fundamental concepts II

• Red-blue-green model.– Add colors red blue and green to various

degrees to get pixels of any color– Additive model

• Cyan-Magenta-Yellow– Uses basic color cyan, magenta, yellow, to

absorb light on the surface – Subtractive color model

Output comes in two forms• Tangible or hardcopy output

– Card puncher– Printer

• Intangible or softcopy output– Monitor display screens– Loudspeaker output

Hardcopy to printers

• Printer prints – character symbols– Graphics

• Output quality is measured in dpi dots per inch

• Printers vary from 60 to 1500 dpi

• 600 dpi seems common

Types of printers: impact

• Forms characters or images by mechanic strikes of a print hammer or wheel.

• One example is a typewriter.• Most common form is the dot matrix printer

– Head with small pins (9, 18, 24)– Strike ribbon against paper– Do 72 to 144 dpi, 30 to 400 chars– Noisy – Image may smear

Types of printers: non-impact

• Form characters and images without physical contact

• Less moving parts, less noise

• Three forms– Laser printer– Inkjet printer– Thermal printer (less frequent)

Laser printer

• Images are produced on a drum

• A laser beam sets electrical charge on dots on the drum

• Magnetically charged powder called toner flies to the electrified dots on the drum

• The drum rolls the toner on the paper

• A second drum burns the toner on the paper

Laser printer performance

• Can print 200 pages per minute provided that the computer can chunk out the data that fast

• Can print a lot of different fonts

• More fancy models can even do color

• Use a page description language to generate the images

Inkjet printer

• Spray tiny, electrically charged drops of ink from 64 nozzles through holes in a matrix onto paper

• There are usually four cartages of colored ink (cyan, magenta, yellow, black)

• Head moves around and software says where to spray

Inkjet printer performance

• Can print color at much less cost than laser printer

• Lower resolution than a color laser printer

• Slow, one page may take up to 10 minutes

• More expensive to operate than a color laser printer when you have to print a lot of color.

Other printers

• Thermal printers– use wax and heat to burn images on special

paper– Expensive to buy, and paper is expensive.– Only for those who require top quality.

• Multifunction printer – Device that can print, scan, copy and fax– When one component is kaputt, you can not

indulge in any of the activities

Softcopy output: monitor

• Size is measured diagonally from corner to corner in inches, not the size of the viewing area

• Common sizes are 13, 15, 17, 19, 21• There are two types

– Cathode-ray tube CRT– Flat panel displays

• All display an image through a number of pixels, individual dots that make it up

Display quality

• Dot pitch is the amount of space between adjacent pixels, usually measure in millimeters

• Resolution is the number of pixels measured as horizontal pixel number × vertical pixel number.

• Refresh rate is the number of times per second the pixels are recharged. > 75 is ok

• Color dept, 8bit, 16bit and 32bit, true color. It is often not necessary to have true color. It is better to have higher resolution and less colors.

Types of flat panel monitors

• Passive matrix display: one transistor controls a whole row or column of pixels. – good for monochrome– but not for color. – less expensive– Lower energy consumption

• Active matrix display, aka thin film transmission TFT: each pixel has its own transistor

CRT monitors

• Have a three rays that paint red blue and green

• They emit beams that hit phosphate in the screen surface

• Light is emitted

• Analogue technology

Moving from CRT to TFT

• Video card still emit analog beam signals to the monitor.

• They have to be converted to the flat panel signal that is digital

• Causes some performance losses.

• Slow conversion to flat panel technology

• Likely to be taken up outside IT, like in art for example

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