Input and Output

Chapters 4 and 5 in Discovering Computers 2000 (Shelly,

Cashman and Vermaat)

Input Devices

• Keyboard

• Pointing Devices– Mouse– Trackball– Touch pad– Pointing stick – Joystick

• Scanner

• Digital camera

• Bar code reader

• Speech Recognition Devices

• Fax

• Microphone

Output Devices

• Printer– “hard copy”

• Monitor– “soft copy”

• Speech synthesizer– e.g. Stephen Hawking– http://www.damtp.cam.ac.uk/user/hawking/computer.html

Digitizing

• Recall that inside the computer, information is “digital”

• That is, it is discrete, as opposed to continuous (“analog”)

• Converting information (e.g. an image) from continuous to discrete is called “digitizing”

Georges Seurat: “A Sunday Afternoon on the Island of La Grande Jatte”

The Sound of Music

• A convention for digitizing sounds is called Musical Instrument Digital Interface (MIDI)

• MIDI is also the name of the port where sound information is brought into or out of the computer

• A common kind of sound file is the .WAV file (they can be big)

They say you want some resolution

• One meaning of the word “resolve” is to break into constituent pieces

• An image, whether it’s input (a scanner or digital camera) or output (monitor or printer), is broken into small pieces

• Each small piece is called a “picture element” or “pixel”

Measuring resolution

• Screen resolution is measured by number of pixels down and across the screen

• 640 480 – 640 pixels across and 480 pixels down – called “VGA” (video graphics array)

• 800 600 – called “super VGA”

• 1024 768 – called “XGA” (extended graphics array)

Measuring resolution II

• Printer and scanner resolution is specified by the number of dots per inch (dpi) – ink-jet and dot matrix printers: 100 to 200 dpi– laser printers: 300-1200 dpi– commercial type-setting machine: 1000 to 2400

dpi– scanner 400 to 600 dpi ?– http://www.zdnet.com/products/scanneruser/index.html

I see your

• After breaking an image into pixels, one assigns numbers to each pixel

• One can use a single bit to represent black or white • An 8-bit scanner or monitor can distinguish 256 shades

of gray or colors• In a 24-bit scanner, 8 bits are used for each primary

color (red, green, blue), giving a total of 16,777,216 colors

• This is called “true color.” It’s close to what the human eye can discern.

• Still one sees many adds for 32-bit color

Bit map• The computer assigns each pixel an address• One builds up the image by “addressing” the

individual pixels• In the simplest scenario, there is one bit

determining the state of each bit (black or white) • Building an image in this fashion is called “bit

mapping”• .bmp files are Microsoft’s version of bit map files

A picture is worth a thousand words … and then some • An 8 1/2 11 inch true-color image at 300

dpi • (8.5)(11)(300)(300)(24)• 201,960,000 bits• 25,245,000 bytes 24 Megabytes• Recall that a 500 page book requires

approx. 2 Megabytes

Another way (vector)

• Instead of having points (dots) as the building blocks of an image, one can use lines, then one stores only the endpoints of the line, instead of every point

• this approach can save on storage• it also makes images scalable (you can

change their size readily) a a a a

Compression and Storage

• One wants to squeeze these files so they don’t take up so much room (memory and/or storage)

• This squeezing is called “compression”– lossless: no info is loss, e.g. TIFF – lossy: some info is lost, e.g. JPG and

GIF (images files used on the web)

CCD’s

• One way to “digitize” an image, i.e. break it into pieces and assign each a number or numbers, uses CCD’s

• CCD stands for “charge-coupled device”

• These devices exploit photoconductors - materials in which the conductivity (ability to send electrical current) depends on the amount of light shining on them

• CCD (digital) cameras are coming into vogue

Photoconductors

• In the light, it’s a good conductor, electrons can move easily

• In the dark, it’s a bad conductor, electrons cannot move

Monitors I. CRT’s

• Cathode ray tube CRT (like television)

• A stream of electrons (a cathode ray) is aimed toward the screen which is coated with various phosphors; the electrons transfer their energy to the phosphors which then glow

• There are phosphors for red and green and blue which can be combined to make all other colors

Monitors II. LCD’s

• CRT’s are OK for desktop computers, but laptops require something smaller and lighter; they need “flat panel displays”

• The most common flat panel display is the liquid-crystal display (LCD)

• liquid crystals are molecules said to be in a state between liquid and solid

• Their optical properties are affected by electric current or fields, hence their use as displays: watches, laptop screens, etc.

How a laser printer works

• Signal from computer to laser (0 or 1, laser on or off)

• Light hits photoconductor, the charged particles that receive the light can move, the others must stay

• Then toner (little black particles) is attracted to the charges left behind

• The paper comes in and heat fuses the toner to the paper

WYSIWYG

• What you see is what you get

• Does what you see on the monitor resemble what is printed out?

• TEX (a scientific word processor) uses escape sequences like \alpha to print the Greek letter

• HTML (hyper text markup language) uses tags like <B>bold</B> to print in bold

Recognition I

• if your image (scanned in as a bitmap) is text, you may want it converted to a text format (ASCII)– typed: easy– handwritten: hard

• This process is referred to as Optical Character Recognition (OCR)

Recognition II

• Voice or speech recognition – speaker independent (vocabulary limited)

• computer trained to “understand” a few words spoken by almost anyone

– speaker dependent (user limited)• computer trained by specific user to “understand”

him or her