VIDEO

VIDEO MONITOR

CRT (Cathode Ray Tube) - places images on the screen by aiming beams of electrons at the back of the display screen. These beams are "directed" by a magnetic mechanism called the Yoke. They strike phosphors, which glow when energized.

LCD (Liquid Crystal Diode) - Have you ever worn polarized sunglasses?

Polarized film and liquid crystals – a sheet (or two) of polarized film and a layer containing liquid crystals (and other stuff...)
Liquid crystals can turn on a dime to prevent light from passing through or being reflected – think Jacques Cousteau and schools of small fish here…
Liquid Crystals do not project light, they filter or reflect it
Color filters then add color
Active Matrix (TFT – Thin Film Transistor)
Passive Matrix – uses a capacitor (slow and some moving objects may disappear)
Native resolution

CRT Monitors

To start off with let me say that the individual components of computer monitors are really not field replaceable units (FRUs). Very A+

Monitors, when plugged in and turned on, contain electrical charges in excess 30,000 volts.
Even when turned off and unplugged some components may retain extremely high voltages for fairly long periods of time.
You should avoid opening monitors up and defer their repair to trained specialists.
If you are dealing with one-piece PC systems (like older Macs, iMacs, or PC iMac-looking clones) you need to be extremely cautious - you could die.

REFRESH - CRT's must be refreshed because the phosphors that make up the screen hold their glow for only a short time.

Vertical refresh rate is measured in Hz (times per second). - (50-160Hz) VGA will have a minimum refresh rate of 70Hz.

Horizontal refresh rate is measured in kHz (thousands of times per second). (30-70kHz).

Interlace - this method of display paints the screen image every other row at a time. It then returns to the top of the screen and paints the rows it missed.

TRIAD - The smallest element on a video display screen. On a color screen a triad is made up of three dots, red, green and blue.

PIXEL (picture element) - A pixel is one or more of those triads treated as a unit.

DOT PITCH - is the distance between the dots in millimeters. Dot pitch influences the clarity of the image.

Dot Pitch


Shadow Mask	Aperture Grill

RESOLUTION - Screen resolution is expressed as the number of pixels wide by the number of pixels high.

Multisync - Monitors that are able to adapt their refresh rates based on resolution.

MPRIII / TCO Compliant - Swedish government standards for allowable video terminal radiation (VLF / ELF).

ADAPTER CARD (DISPLAY ADAPTER)

Before your monitor can display an image it must first be sent an image from the computer. A video adapter - or video display board – or display adapter - is an expansion board that plugs into the "bus" or "port" of a desktop computer.

It converts the images created in the computer to the electronic signals required by the monitor. It determines the maximum resolution, maximum refresh rate, and the number of colors that can be sent to the monitor.
The monitor must be equally capable of handling the highest resolution and refresh. The kind of adapter and amount of video RAM on the video adapter has a direct effect on the number of visible colors, the displayed resolution, and the perceived speed of video movement.

VGA (SVGA) is the current standard for display adapters.

640 x 480 x 16 (and up!)

Care and feeding

Cables


For VGA	For that Mac in your life	For DVI (Digital Visual Interface - LCDs)

Cleaning - Very A+

Clean the outside of the monitor (case) with Simple Green, 409, or a similar cleaner.

Spray a cloth with glass cleaner and wipe the screen. Be sure to use a clean, soft cloth.

ADAPTER CARD (DISPLAY ADAPTER)

It converts the images created in the computer to the electronic signals required by the monitor. It determines the maximum resolution, maximum refresh rate, and the number of colors that can be sent to the monitor.
The monitor must be equally capable of handling the highest resolution and refresh. The kind of adapter and amount of video RAM on the video adapter has a direct effect on the number of visible colors, the displayed resolution, and the perceived speed of video movement.

Early adapter standards

Although no longer on the cutting edge of video, IBM set the early standards for video display adapters. Historically these standards were:

MDA (Monochrome Display Adapter)
CGA (Color Graphics Adapter)
EGA (Enhanced Graphics Adapter)
VGA (Video Graphics Array)
SVGA (Super VGA)
XGA (eXtended Graphics Array)

With the exception of VGA and SVGA these standards are seldom referred to anymore. The first three are obsolete and the last three are simply referred to as VGA or SVGA. When shopping for a video card you will be presented more with information regarding resolution, number of colors, amount of memory and special features than with what standard the card is - everything these days is at least VGA!

VIDEO RAM (VRAM) - Very A+

VRAM - dual ported, memory can be access by both input and output processes at the same time – many mid-90’s Macs use VRAM
WRAM - dual ported, but cheaper than VRAM
SGRAM - can sync with bus for fast access and low latency

Minimum Video RAM Required for Different Resolutions - Very A+

Here is the math: H * V * (bit depth / 8) (round up)
800 * 600 * (16 / 8) = 960,000
800 * 600 * (24 / 8) = 1,440,000

Resolution	256 colors (8-bit)	65,000 colors (16-bit)	16.7 million colors (24-bit, true color)
640x480	512K	1 MB	1 MB
800x600	512K	1 MB	2 MB
1,024x768	1 MB	2 MB	4 MB
1,152x1,024	2 MB	2 MB	4 MB
1,280x1,024	2 MB	4 MB	4 MB
1,600x1,200	2 MB	4 MB	6 MB (or 8MB)

Let’s see the big picture

For BASIC Functions of a Video Card

1 - The digital data arives from the system bus to the video chip set on the video card

2 - The video chip set writes the video data to video memory on the card

3 - The data stored in video memory is passed to the digital analog converter (RAM-DAC)

4 - REM-DAC passesthe analog data to the monitor

Changing Video - Very A+

The "Display Properties" dialog box can be reached by right-clicking on the desktop or from the "Display" applet in the Control Panel. We control our display (and more) from here.

Changing Video Advanced

The Advanced button gives you access to many more control features. Do not set the refresh higher than that allowed by your monitor - damage may ensue! If you make a mistake and scramble the screen, the system will default back in 15 seconds – or press the ESC key. Very A+

The "optimal" question

The adapter reads display data channel (DDC) information from the monitor and uses it to calculate:

Which resolutions are supported
What is the "optimal" refresh rate for each supported resolution
ALL possible modes are offered, and it is up to you to choose a resolution and refresh rate that works with your monitor

When choosing a quality video card these four issues come to mind:

RAMDAC – 300MHz and up
Fill Rate (applying color to graphics objects in Mpixels/sec) – 200 and up
Amount of memory – 16MB and up
Kind of memory – EDO, SDRAM, DDRAM, RDRAM (Rambus)

Touch screen - A+

Touch screen monitors have become more affordable and thus more commonplace. Here are two basic systems that are used to recognize touch:

Resistive
- Consists of three layers. A conductive, a resistive and a scratch resistant layer
- A change in an electrical field is created where the user touches the screen and the two layers come together
- Can read any touch
Capacitive
- A layer that stores electrical charge is placed on the glass panel of the monitor.
- When a user touches the monitor with a finger (or toe), some of the charge is transferred to the user, so the charge on the capacitive layer decreases
- Needs a human touch – a computer "track pad" works in much the same way

A touch screen may be built into a monitor or added as add-on. Touch screen computer monitors will also have an output path (serial or USB) to send their touch data to the computer.

Edited (2003) By Vlad Magero