LIS 508 lecture 6 output devices Thomas Krichel

LIS 508 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, 8 bit, 16 bit and 32 bit, 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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