itec 1000 introduction to information technologies types of displays two main types –crt (cathode...

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


Layout for a display


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: 28 = 256)


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”


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)


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


Resolution

Bits per pixel

8 bit 16 bit

65K colors

24 bit

16M colors

640 x 480 300 600 900

800 x 600 468.75 937.5 1406.25

1024 x 768 768 1536 2304

1152 x 1024 1152 2304 3456

1280 x 1024 1280 2560 3840

1600 x 1200 1875 3750 5625

Video RAM (KB) Per Image

See previous slide for calculations


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…


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:

640

480Z1. Z = (6402 + 4802)1/2 = 800

2. 1 mm = 0.039 inch

Dot pitch = 15 / 800 inches= 0.01875 inches= 0.01875 / 0.039 mm= 0.481 mm

Notes:


Dot Pitch Illustrated

Pixel

0.481 mm


Dot Pitch Image Table

ResolutionDisplay Size

14” 15” 17” 19” 21”

640 x 480 0.45 0.48 0.54 0.61 0.67

800 x 600 0.36 0.38 0.44 0.49 0.54

1024 x 768 0.28 0.30 0.34 0.38 0.42

1152 x 1024 0.23 0.25 0.28 0.32 0.35

1280 x 1024 0.22 0.23 0.27 0.30 0.33

1600 x 1200 0.18 0.19 0.22 0.24 0.27

Note: Dot pitch figures in mm (millimeters)


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


CRT Display

Rev: Fig 9.21 pg 267 ff


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


Figure 9.17 Use of a color transformation table

Color Transformation Table G B


Figure 9.20 Display example: (a) desired display, (b) video memory contents, (c) color palette table, (d) color signals


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


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


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


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


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


VGA/SVGA/XGA PinoutsPin Signal

1 Red

2 Green

3 Blue

4 ID bit 2

5 Ground

6 Red return

7 Green return

8 Blue return

9 -

10 Sync return

11 ID bit 0

12 ID bit 1

13 Horizontal sync

14 Vertical sync

15 -

DE15 connector


S-video Pinouts

Pin Signal

1 Ground

2 Ground

3 Y (luminance)

4 C (Chrominance) 4-pin mini-DIN connector


Plan

• Printers

• Scanners


Printers

• Main types:– Impact– Laser– Ink jet

Impact


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)


Printers

• Main types:– Dot matrix (sample impact)– Laser– Ink jet


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)


Dot Matrix Print Head

Front view Side view

Print wires(e.g., 12)

One print wire


Dot Matrix Impact Printing

Printwire

Ribbon

Paper

Platen

Side view Side view Front view

Paper


Illustration


Creating a Gray Scale


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)


Dot Matrix Printer Example

FormsMaster 8000 by Printek, Inc.

http://www.printek.com

Specifications

• 800 cps

• 400 lpm

• 6-part forms (max)


Printers

• Main types:– Dot matrix– Laser– Ink jet


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 1000th or 1600th of an inch.

Laser

Spinningmirror

Photosensitivedrum


Top View of Rotating Mirror

Drum Rotating Mirror: This one has eightfaces

Laser light source


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


Operation of a Laser Printer3. 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

Chargewire


Operation of a Laser Printer4. 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.

Coronawire

Fusingsystem


Specifications

• ppm– Pages per minute– Typically 4-10 ppm

• dpi– Dots per inch– Typically 600-1200 dpi


Laser Printer Example

Laserjet 5000 Series from Hewlett Packard Co.

(http://www.hp.com)


Printers

• Main types:– Dot matrix– Laser– Ink jet


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


How it worksCharacters 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.


Plan

• Printers

• Scanners


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 300-600 dpi (dots per inch).


Scanners

• Three main types– Flatbed– Sheet-fed– Handheld


Flatbed Scanner Example


Sheet-fed Scanner Example

OfficeJet Series 700 from Hewlett Packard Co

(http://www.hp.com)


Handheld Scanner Example

QuickScan GP Bar Code Scanner from PSC, Inc.

(http://www.pscnet.com)

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