ITEC 1000 Introduction to Information Technologies Types of Displays Two main types –CRT (cathode ray tubes) –LCD (liquid crystal display) OLED Related terms –Monitor or screen A display is often called a “monitor” or “screen” However, the term “monitor” usually refers to the entire box, where as “screen” often implies just a sub-assembly within the box

ITEC 1000 Introduction to Information Technologies Layout for a display

ITEC 1000 Introduction to Information Technologies Pixels A Pixel is a “picture element” –a single point in a graphic image –A graphics display is divided into thousands (or millions) of pixels arranged in rows and columns –The pixels are so close together, they appear connected –The number of bits used to represent each pixel determines how many colours or shades of grey can be represented –For a B&W (black and white) monitor, each pixel is represented by 1 bit –With 8 bits per pixel, a monitor can display 256 shades or grey or 256 colours (Note: 2 8 = 256)

ITEC 1000 Introduction to Information Technologies Display Size Usually specified in “inches” Value cited is the diagonal dimension of the raster -- the viewable area of the display E.g., a 15” monitor 15”

ITEC 1000 Introduction to Information Technologies Resolution Resolution is the number of pixels on a screen display Usually cited as n by m –n is the number of pixels across the screen –m is the number of pixels down the screen Typical resolutions range from… –640 by 480 (low end), to –1,600 by 1,200 (high end)

ITEC 1000 Introduction to Information Technologies Video RAM Requirements Total number of pixels is n  m Examples –640  480 = 307,200 pixels –1,600  1,200 = 1,920,000 pixels Video RAM required equals total number of pixels times the number of bits/pixel Examples –640  480  8 = 2,457,600 bits = 307,200 bytes = 300 Kbytes –1,600  1,200  24 = 46,080,000 bits = 5,760,000 bytes = 5,625 Kbytes = 5.49 Mbytes

ITEC 1000 Introduction to Information Technologies Resolution Bits per pixel 8 bit16 bit 65K colors 24 bit 16M colors 640 x x x x x x Video RAM (KB) Per Image See previous slide for calculations

ITEC 1000 Introduction to Information Technologies Dot Pitch Dot pitch is a measure of the diagonal distance between phosphor dots (pixels) on a display screen One of the principal characteristics that determines the quality of a display The lower the number, the crisper the image Cited in mm (millimeters) Typical values range from 0.15 mm to 0.30 mm Note –Dot pitch, as specified, is the capability of the display –For a particular image, dot pitch can be calculated as…

ITEC 1000 Introduction to Information Technologies Dot Pitch Image Example Q: What is the dot pitch of an image displayed on a 15” monitor with a resolution of 640 by 480? A: Z 1.Z = ( ) 1/2 = mm = inch Dot pitch= 15 / 800 inches = inches = / mm = mm Notes:

ITEC 1000 Introduction to Information Technologies Dot Pitch Illustrated Pixel mm

ITEC 1000 Introduction to Information Technologies Exercise – Dot Pitch Image Q: What is the dot pitch of an image displayed on a 19” monitor with a resolution of 1,280 by 1,024? A: Dot pitch= 19 / inches = inches = / mm = 0.30 mm Note: Z = ( ) 1/2 =

ITEC 1000 Introduction to Information Technologies Dot Pitch Image Table Resolution Display Size 14”15”17”19”21” 640 x x x x x x Note: Dot pitch figures in mm (millimeters)

ITEC 1000 Introduction to Information Technologies Colour Displays CRT displays –each pixel is composed of three superimposed dots: red, green, and blue –Hence, RGB display –The three dots are created by three separate beams –Ideally, the three dots should converge at the same point, however, in practice there is a small amount of convergence error, and this makes the pixels appear fuzzy LCDs –Colour is created by filtering/blocking different frequencies of light

ITEC 1000 Introduction to Information Technologies CRT Display Rev: Fig 9.21 pg 267 ff

ITEC 1000 Introduction to Information Technologies Operation of a CRT Display A CRT display contains a vacuum tube At one end are three electron guns, one each for red, green, and blue At the other end is a screen with a phosphorous coating The three electron guns fire electrons at the screen and excite a layer of phosphor Depending on the beam, the phosphor glows, either red, green, or blue

ITEC 1000 Introduction to Information Technologies Figure 9.17 Use of a color transformation table Color Transformation Table G B

ITEC 1000 Introduction to Information Technologies Figure 9.20 Display example: (a) desired display, (b) video memory contents, (c) color palette table, (d) color signals

ITEC 1000 Introduction to Information Technologies Operation of an LCD Two sheets of polarizing material with a liquid crystal solution between them An electric current passed through the liquid causes the crystals to align so that light cannot pass through them Each crystal, therefore, acts like a shutter, either allowing light to pass through or blocking the light

ITEC 1000 Introduction to Information Technologies Active-Matrix Display A type of liquid crystal display in which the image is refreshed more frequently than in conventional (passive matrix) displays Most common type of active-matrix display is known as TFT (thin-film transistor) The terms active matrix and TFT are used interchangeably

ITEC 1000 Introduction to Information Technologies Video Interfaces (1 of 2) Composite video –Definition: a video interface in which all the colour and sync information is contained in one signal –Contrast with RGB –TVs in North America use composite video RGB (Red, Green, Blue) –Definition: a video interface in which the red, green, and blue signals, and the horizontal and vertical sync signals, are separate –Computer monitors use RGB

ITEC 1000 Introduction to Information Technologies Video Interfaces (2 of 2) S-video –A technology for transmitting video signals over a cable by dividing the video information into two separate signals: one for colour (chrominance, C), and one for brightness (luminance, Y) –Also called Y/C video –Televisions (internally) are designed for separate luminance and chrominance signals –Computer monitors are designed for separate red, green, and blue signals

ITEC 1000 Introduction to Information Technologies RGB Video Standards A variety of standards exist for delivering RGB signals to a video display monitor Developed and consolidated by VESA (Video Electronics Standards Association) Examples –VGA – video graphics adapter –SVGA – super-VGA –XGA – extended graphics adapter

ITEC 1000 Introduction to Information Technologies VGA/SVGA/XGA Pinouts PinSignal 1Red 2Green 3Blue 4ID bit 2 5Ground 6Red return 7Green return 8Blue return 9- 10Sync return 11ID bit 0 12ID bit 1 13Horizontal sync 14Vertical sync 15- DE15 connector

ITEC 1000 Introduction to Information Technologies S-video Pinouts PinSignal 1Ground 2 3Y (luminance) 4C (Chrominance) 4-pin mini-DIN connector

ITEC 1000 Introduction to Information Technologies Plan Printers Scanners

ITEC 1000 Introduction to Information Technologies Printers Main types: –Impact –Laser –Ink jet Impact

ITEC 1000 Introduction to Information Technologies Impact vs. Non-Impact Impact printers physically transfer a dot or shape to the paper Include dot-matrix, belt, & solid line printers Non-impact printers spray or lay down the image Impact printers remain important because they can print multi-part forms (eg: carbon or NCR copies)

ITEC 1000 Introduction to Information Technologies Printers Main types: –Dot matrix (sample impact) –Laser –Ink jet

ITEC 1000 Introduction to Information Technologies How it works ( Impact Type Dot-Matrix ) A print-head moves back-and-forth in front of forms (paper) on which characters or graphic images are transferred. The print-head contains numerous wires, typically from 9 to 24. Each wire is part of a solenoid-like unit. An electrical pulse applied to the solenoid creates a magnetic field which forces the wire to move briefly forward then backward. As the wire moves forward, it strikes a print ribbon containing ink. The impact transfers an ink dot to the paper. The paper is supported from behind by a platen. (a hard flat piece)

ITEC 1000 Introduction to Information Technologies Dot Matrix Print Head Front view Side view Print wires (e.g., 12) One print wire

ITEC 1000 Introduction to Information Technologies Dot Matrix Impact Printing Print wire Ribbon Paper Platen Side view Front view Paper

ITEC 1000 Introduction to Information Technologies Illustration

ITEC 1000 Introduction to Information Technologies Creating a Gray Scale

ITEC 1000 Introduction to Information Technologies Specifications cps –characters per second –Varies by quality of print (e.g., draft vs. final (NLQ)) lpm –lines per minute (related to cps) Forms –Maximum number of layers of paper that can by printed simultaneously –Specified as n-part forms (e.g., 4-part forms) mtbf –Mean time between failure (e.g., 6000 hours)

ITEC 1000 Introduction to Information Technologies Dot Matrix Printer Example FormsMaster 8000 by Printek, Inc. Specifications 800 cps 400 lpm 6-part forms (max)

ITEC 1000 Introduction to Information Technologies Printers Main types: –Dot matrix –Laser –Ink jet

ITEC 1000 Introduction to Information Technologies Operation of a Laser Printer Four steps –A laser is fired in correspondence to the dots to be printed. A spinning mirror causes the dots to be fanned out across the drum. The drum is photosensitive. As a result of the laser light, the drum becomes electrically charged wherever a dot is to be printed. –The drum rotates to the next line, usually 1000 th or 1600 th of an inch. Laser Spinning mirror Photosensitive drum

ITEC 1000 Introduction to Information Technologies Top View of Rotating Mirror Drum Rotating Mirror: This one has eight faces Laser light source

ITEC 1000 Introduction to Information Technologies Operation of a Laser Printer 2.As the drum continues to rotate, the charged part of the drum passes through a tank of black powder called toner. Toner sticks to the drum wherever the charge is present. Thus, the pattern of toner on the drum matches the image. Toner

ITEC 1000 Introduction to Information Technologies Operation of a Laser Printer 3.A sheet of paper is fed toward the drum. A charge wire coats the paper with electrical charges. When the paper contacts the drum, it picks up the toner from the drum Paper Charge wire

ITEC 1000 Introduction to Information Technologies Operation of a Laser Printer 4.As the paper rolls from the drum, it passes over a heat and pressure area known as the fusing system. The fusing system melts the toner to the paper. The printed page then exits the printer. As the same time, the surface of the drum passes over another wire, called a corona wire. This wire resets the charge on the drum, to ready it for the next page. Corona wire Fusing system

ITEC 1000 Introduction to Information Technologies Specifications ppm –Pages per minute –Typically 4-10 ppm dpi –Dots per inch –Typically dpi

ITEC 1000 Introduction to Information Technologies Laser Printer Example Laserjet 5000 Series from Hewlett Packard Co. (

ITEC 1000 Introduction to Information Technologies Printers Main types: –Dot matrix –Laser –Ink jet

ITEC 1000 Introduction to Information Technologies Background Inkjet technology was developed in the 1960s First commercialized by IBM in 1976 with the 6640 printer Cannon and Hewlett Packard developed similar technology Also called bubble jet

ITEC 1000 Introduction to Information Technologies How it works Characters and graphics are 'painted‘ line by line to from a pattern of dots as a print head scans horizontally across the paper. An ink-filled print cartridge is attached to the inkjet's print head. The print head contains 50 or more ink-filled chambers, each attached to a nozzle. An electrical pulse flows through thin resistors at the bottom of each chamber. When current flows through a resistor, the resistor heats a thin layer of ink at the bottom of the chamber to more than 900 degrees Fahrenheit for several millionths of a second. The ink boils and forms a bubble of vapour. As the vapour bubble expands, it pushes ink through the nozzle to form a droplet at the tip of the nozzle. The droplet sprays onto the paper. The volume of the ejected ink is about one millionth that of a drop of water from an eye-dropper. A typical character is formed by an array of these drops 20 across and 20 high. As the resistor cools, the bubble collapses. The resulting suction pulls fresh ink from the attached reservoir into the firing chamber.

ITEC 1000 Introduction to Information Technologies Plan Printers Scanners

ITEC 1000 Introduction to Information Technologies How it works A scanner works by digitizing an image. A scanning mechanism consists of a light source and a row of light sensors. As light is reflected from individual points on the page, it is received by the light sensors and translated to digital signals that correspond to the brightness of each point. Colour filters can be used to produce colour images, either by providing multiple sensors or by scanning the image three times with a separate colour filter for each pass. The resolution of scanners is similar to that of printers, approximately dpi (dots per inch).

ITEC 1000 Introduction to Information Technologies Scanners Three main types –Flatbed –Sheet-fed –Handheld

ITEC 1000 Introduction to Information Technologies Flatbed Scanner Example

ITEC 1000 Introduction to Information Technologies Sheet-fed Scanner Example OfficeJet Series 700 from Hewlett Packard Co (

ITEC 1000 Introduction to Information Technologies Handheld Scanner Example QuickScan GP Bar Code Scanner from PSC, Inc. (