Monitors&

Video Cards

Supporting I/O Devices

PC Displays

Primary output device of a computer is the monitor Monitor, Video Display, VDT, Screen…..

Two necessary components for video output Video controller Monitor

PC Displays

CRT- Cathode Ray TubeA CRT monitor uses a vacuum tube

to contain the beam of electrons used to produce the image

Two Types: Regular Flat-technology monitors

PC Displays Flat panel monitors are built to receive either an

analog signal or a digital signal from the video card and have two ports on the monitor to accommodate either signal

Flat Panel Technology LCD : Liquid Crystal Display

PDP: Plasma Display Panel A gas plasma display

ELD: Electroluminescent display LED: Light Emitting Diode

Display Subsystem

Each PC’s display subsystem consists of three parts: Video Display Adapter

creates and holds the image information Monitor

displays the information Cable

connects the video adapter to the monitor

Display Basics

Pixels In a CRT display device, the smallest

possible pixel is actually a dot trio called a triada red, green and blue phosphor dot

set RGB Model - most common model

for PC video displays

Display Basics

An electronic beam is used to strike the phosphor causing it to emit light

Plates on the top, bottom and sides of the CRT tube control the direction of the beam

Depending on the intensity of the beam, the dot trio emits a range of colors created by mixing the 3 colors: red, blue and green

Computer Display Systems

CRT- Cathode Ray tube- the same technology employed by your television- an electron gun scans the screen causing special chemicals called ‘phosphors’ to glow- the gun scans from top to bottom, left to right

Video Adapter- an expansion board or integrated device that renders characters for display in response to commands from the computer- it tells the display device how to draw the graphic

Video Technologies Monochrome- two color video- text only with a resolution of 720

x 350 Color Graphics Adapter- CGA- four colors- 320 x 200

resolution for graphics, 640 x 200 for two color Enhanced Graphics Adapter- EGA- 16 colors- 320 x 200

graphics, 640 x 350 text Video Graphics Array- VGA- introduced with the IBM AT form

factor motherboards- used an analog signal- 256KB of video memory on board- 16 colors at 640 x 480 or 256 colors at 320 x 200

Super Video Graphics Array- introduced by the Video Electronics Standards Association- 65, 536 colors at 640 x 480, 256 colors at 800 x 600 or 16 colors at 1,024 x 768

Extended Graphics Array- IBM’s answer to the SVGA, XGA could only use the MCA expansion bus- it also used interlacing, or scanning every other line on each pass- offered the same resolution options as the SVGA

Display Quality Measurements

Dot Pitch- the shortest distance between two dots of the same color on the monitor Measured in millimeters The lower the number, the sharper the image .28mm is considered average- anything smaller is

great

Refresh Rate- vertical scan frequency- how many times in one second does the electron beam redraw the screen? The standard is 60Hz for VGA

Displays Most desktop displays use a

cathode ray tube (CRT), while portable computing devices such as laptops incorporate liquid crystal display (LCD)

Because of their slimmer design and smaller energy consumption, monitors using LCD technologies are beginning to replace the venerable CRT on many desktops

CRT Monitor

How a CRT monitor works

DAC Converters

Digital-to-Analog (DAC) Convertersspecial integrated circuits used by

display adapters

Two Ways to Paint Image on Screen:

Vector Displays the electronic beam used to create

the image is moved across the screen in a pattern similar to moving a pen or pencil over a piece of paper

Two Ways to Paint Image on Screen:

Raster-Scan the screen is painted line by line from left

to right the electronic beam is played across the

screen from left to right in a straight horizontal line - moves to left and goes to next line

Most CRTs and LCDs use Raster-Scan to paint images to screen

Liquid Crystal Displays Active Matrix- each LCD pixel has a transistor

behind it to activate or deactivate the crystal Very crisp and easy on the eyes Very power intensive- severely limited the amount of time a

laptop could run on battery power Passive Matrix- two rows of transistors marking the x

and y coordinates of a grid- a signal voltage line is sent to the x and y coordinates, turning the corresponding pixel dark Requires less power Sacrifices image quality Response of the screen to rapid change is poor

LCD panels An LCD is made with either

a passive matrix or an active matrix display display grid The passive matrix LCD,

which is older technology, has a grid of conductors with pixels located at each intersection in the grid.

The active matrix LCD is also known as a thin film transistor (TFT) display, which has a transistor located at each pixel intersection, requiring less current to control the luminance of a pixel.

LCD panels A color LCD must have

three subpixels with red, green and blue color filters to create each color pixel

Through the careful control and variation of the voltage applied, the intensity of each subpixel can range over 256 shades

Combining the subpixels produces a possible palette of 16.8 million colors

LCD technology

LCDs today employ several variations of liquid crystal technology, e.g. ferroelectric liquid crystal (FLC)

Display size is limited by the quality-control problems faced by manufacturers

The more transistors that are put in display, the chances are that the will be defective

Manufacturers of existing large LCDs often reject about 40 percent of the panels that come off the assembly line

LCD Monitors

In general, an LCD panel is made of two polarized planes of glass placed at right angles (90 degrees) to each other.

Sandwiched between the glass is a layer of liquid crystals.

Behind the back panel is a fluorescent light source that tries to get through the two misaligned panels of glass.

In the default state, the light is blocked, and the panels appear black.

Unless there is a light behind the panel or a very bright light reflecting through the front panel and then off the back panel, an LCD cannot display anything.

LCD Monitors

The LCD monitors use the CMY (cyan, magenta, yellow) process of building colors

Triads of three crystals (each being able to pass only one primary color) are put together in a matrix

By turning on one of the crystals in each triad the same effect can be produced as with an electron beam and phosphorus in the CRT monitors

LCD Monitors

Each liquid crystal is in a matrix or grid (rows and columns) with very thin wires leading to a set of of switches along the top and side edges of the glass panels

When electric current is sent to a specific X-Y location on the grid, the liquid crystal is activated

LCD monitors can be passive matrix or active matrix

LCD Monitors

Passive Matrix One transistor switch per row and column That is, for an 640x480 VGA LCD panel,

the monitor requires 640 transistor switches along the side and 480 transistor switches along the top to produce the 640x480 pixels or dots of light

LCD Monitors Active Matrix

The fundamental difference between the passive matrix and the active matrix is the number of transistor switches on the panel:

The active matrix gives every liquid crystal its own switch.

This speeds up the process of pinpointing a specific X-Y co-ordinate and also provides greater control over the crystal.

LCD Monitors

The three main types of active-matrix LCD panels are:TFT - Thin Film TransistorsMIM - Metal-Insulator-MetalPALC - Plasma Addressed Liquid

Crystal

Maximum Resolution and Dot Pitch

Resolution refers to the number of individual dots of color, known as pixels, contained on a display. Resolution is typically expressed by identifying the number of pixels on the horizontal axis (rows) and the number on the vertical axis (columns), such as 640x480

Dot Pitch is the measure of how much space there is between a display's pixels. When considering dot pitch, remember that smaller is better. Packing the pixels closer together is. fundamental to achieving higher resolutions

Resolution

For both monitors and printers we are interested in the resolution – how small are the pixels (tiny dots)?

Typical monitors have 640 480 or 800 600 with a screen size of 15-17 inches (measured diagonally).

For printers the resolution is in pixels or dots per inch, typically 600 dpi for a laser printer.

Refresh Rate In monitors based on CRT technology, the

refresh rate is the number of times that the image on the display is drawn each second.

Refresh rates are very important because they control flicker, and you want the refresh rate as high as possible.

Too few cycles per second and you will notice a flickering, which can lead to headaches and eye strain.

Color Depth

The combination of the display modes supported by your graphics adapter and the color capability of your monitor determine how many colors can be displayed.

For example, a display that can operate in SVGA mode can display up to 16.8 million colors because it can process a 24-bit-long description of a pixel. The number of bits used to describe a pixel is known as its bit depth.

With a 24-bit bit depth, 8 bits are dedicated to each of the three additive primary colors -- red, green and blue. This bit depth is also called true color because it can produce the 10,000,000 colors discernible to the human eye

Simply put, color bit depth refers to the number of bits used to describe the color of a single pixel. The bit depth determines the number of colors that can be displayed at one time

Color Depth ChartBit-Depth Number of Colors

1 2(monochrome)

2 4(CGA)

4 16(EGA)

8 256(VGA)

16 65,536(High Color, XGA)

24 16,777,216(True Color, SVGA)

32 16,777,216(True Color + Alpha Channel)

2

Things to Consider Display technology - Currently, the choices are

mainly between CRT and LCD technologies. Cable technology - VGA and DVI are the two most

common. Viewable area (usually measured diagonally) Aspect ratio and orientation (landscape or portrait) Scan or Refresh Rate Interlace Features Dot pitch Resolution Color depth Amount of power consumption

Features

Two measures describe the size of your display: The aspect ratio and the screen size.

Aspect Ratio: Most computer displays, like most televisions, have an aspect ratio of 4:3

This means that the ratio of the width of the display screen to the height is 4 to 3.

Screen Size How to Measure Desktop vs. Laptop

Features Scan or Refresh Rate, or vertical scan rate

The time it takes for the electronic beam to fill the screen with lines from top to bottom

The number of times that the image on the display is drawn each second.

If your CRT monitor has a refresh rate of 72 Hertz (Hz), then it cycles through all the pixels from top to bottom 72 times a second.

Control flicker You want the refresh rate as high as possible

Standard rate established by the Video Electronics Standards Association (VESA) is 70Hz, or 70 refreshes per second

Features Multiscan

Multiscan monitors support a variety of refresh rates and can support different video cards

Fixed frequency monitors only support a single refresh rate

Interlace features Interlaced monitors draw a screen in 2 passes,

hitting the even lines first, then the odd lines Non-interlaced monitors draw the entire screen in

1 pass

Features Dot Pitch

The distance between adjacent dots on the screen. The smaller the dot pitch, the higher the quality of

the image. A high-quality monitor should have a dot pitch of no

more than .28mm A display normally can support resolutions that

match the physical dot (pixel) size as well as several lesser resolutions.

For example, a display with a physical grid of 1280 rows by 1024 columns can obviously support a maximum resolution of 1280x1024 pixels but it usually also supports lower resolutions such as 1024x768, 800x600, and 640x480.

Monitors Resolution

A measure of how many dots on the screen are addressable by software

Each addressable location is called a pixel (picture element)

Most monitors offer a resolution of 1024 x 768 or higher

The video controller card as well as the monitor must be capable of supporting the chosen resolution.

Resolutions are set from the Control Panel in Windows 9X

Features

Color Depth The combination of the display modes supported

by your graphics adapter and the color capability of your monitor determine how many colors can be displayed.

Bit Depth : The number of bits used to describe a pixel is known as its bit depth.

For example: with a 24-bit bit depth, 8 bits are dedicated to each of the three additive primary colors -- red, green and blue. This bit depth is also called true color because it can produce the 10,000,000 discernible colors.

Bit-Depth Number of Colors

12

(monochrome)

24

(CGA)

416

(EGA)

8256

(VGA)

1665,536

(High Color, XGA)

2410,000,000

(True Color, SVGA)

3216,777,216

(True Color + Alpha Channel)

Features Power consumption

Varies greatly with different technologies. CRTs are somewhat power-hungry, at about 110

watts for a typical display, especially when compared to LCDs, which average between 30 and 40 watts.

Green monitor In a typical home computer setup with a CRT-

based display, the monitor accounts for over 80 percent of the electricity used!

Monitor that meets the EPA Energy Star program Uses 100 to 150 watts of electricity with no more

than 30 watts being used when the screen saver is on

MonitorsFeature Description

Screen Size Typically 14, 15, 17 or 21 inch - refers to diagonal lengthof the lighted screen. It is often shorter than advertised.

Refresh Rate Vertical scan rate - time it takes an electronic beam tofill screen. Should be minimum of 70Hz (70 times/sec.)

Interlaced Only refreshes half the screen on every pass.

Dot Pitch Distance between adjacent dots. Ex: .28mmThe smaller the pitch, the higher the quality.

Resolution How many spots or pixels are on screen. Ex: 640 x 480

Multiscan Monitors that offer a variety of refresh rates.

Green Monitor Supports EPA Energy Star program, uses no more than 30 watts and can go into sleep mode after inactivity.

Some Features of a Monitor

Monitors

ELF (extremely low frequency) emissions

When matching a monitor to a video card, consider matching a 14-inch monitor with a low-end video card 15-inch monitor with a midrange card 17-inch or larger monitor with a high-end

card for best performance

Display Adapter orGraphics Card

Creates and holds the image information Older technology: specialized circuitry on the system

board Newer technology: a Plug-In Card - often referred to

as the PC’s Video Card Graphics cards are known by many names, such as:

Video cards Video boards Video display boards Graphics boards Graphics adapter cards Video adapter cards Graphics Accelerators

Display Adapter Standards

IBM original: MDA - Monochrome Display Adapter

MGA - Monochrome Graphic Adapter CGA - Color Graphics Adapter

1981 – IBM - 4 colors EGA - Enhanced Graphics Adapter

1984 - IBM integrated color and monochrome systems – 16 colors

Display Adapter Standards

VGA - Video Graphics Array 1987 - IBM

VGA became the industry standard and further extensions were developed: SVGA - Super VGA AVGA - Accelerated VGA - supports

Windows Graphics XGA – Extended Graphics Array

1990 - IBM

Display Adapter Standards

UXGA - Ultra Extended Graphics Array Most displays sold today support the

UXGA standard. UXGA can support a palette of up to 16.8

million colors and resolutions of up to 1600x1200 pixels, depending on the video memory of the graphics card in your computer

Display Adapter Standards

A typical UXGA adapter takes the digital data sent by application

programs stores it in video random access memory

(VRAM) or some equivalent uses a digital-to-analog converter (DAC) to

convert it to analog data for the display scanning mechanism

Once it is in analog form, the information is sent to the monitor through a VGA cable.

Display Adapter Standards

DVI – Digital Video Interface Since today's VGA adapters do not fully

support the use of digital monitors, a new standard, Digital Video Interface (DVI) has been designed for this purpose.

DVI keeps data in digital form from the computer to the monitor, virtually eliminating signal loss (degradation).

Will need a DVI monitor with a DVI compliant graphics card.

Graphics/Video Card

An expansion card responsible for Receiving data and instructions from the CPU Processing the data Sending the results to the monitor

Two main features of a video card The bus it uses (influences speed and

performance) Amount of video RAM it has or can support

Graphics/Video Card

Four basic functions of a video card

Video Card Performance

Performance on the video card is affected by: Chip set Memory RAM DAC Bus speed and size

Methods of improving performance Dual-porting Place a processor on the video card to make it a

graphics accelerator

Graphics Accelerator A type of video card that has its own

processor to boost performance Necessary with the demands that graphic

applications make in the multimedia environment

Processor is specifically designed to manage video and graphics

Their features reduce the burden on the system board CPU and perform the function much faster than the system board CPU

Graphics Accelerator Features MPEG decoding 3-D graphics Dual porting Color space conversion Interpolated scaling EPA green PC support Digital output to flat panel display monitors Applications support for popular high-

intensity graphics software

Video Memory

Necessary to handle large volume of data generated by increased resolution and color

Stored on video cards as memory chips

How Much Video Memory Is Needed?

Determined by Screen resolution (measured in pixels) Number of colors (color depth) Enhancements to color information called

alpha blending

Types of Video Memory

VRAM (video RAM) MDRAM (multibank DRAM) SGRAM (synchronous graphics RAM) WRAM (Window RAM) 3D RAM