HDTV For The Non-Geek

A free article on Technology

By: Brian Bradshaw

The FCC standards for HDTV broadcast become effective next year (February 17, 2009). The amount of information to be digested is intimidating, even for the professional. The old hardware does not become obsolete, but it will require a tuner to convert from the new signal, to the old signal. If you have cable TV, this will be taken care of by the cable company.

However, this might be a good time to upgrade your hardware. The new standard offers a much better picture. In the current world of digital projectors, LCD, LCOS, Plasma, and DLP are the four different kinds of televisions that dominate the HDTV market. Each has unique advantages over the other. Plasma and some of the LCD screens can be mounted on the wall, although surveys find that few people do mount them on the wall. DLP and LCOS and some of the LCD units are both projector technologies. Rear projector units are usually the most cost-effective. The size of some systems is now less than 12 inches in depth.

Video quality on the best projectors now surpasses that available in a conventional commercial movie theater. When reviewing information about the different techniques, pay attention to the source of the information (duh!). A manufacturer of one technology will probably be biased in favor of that technique.

Different System Types:

Traditional TV:
also called direct view, has the images displayed on a picture tube (Cathode Ray Tube). LCD (Liquid Crystal Display) and Plasma TV can also be direct view. The LCD and Plasma TV systems are the "flat-panel" units.

Rear Projection TV (RPTV):
uses a combination of mirrors and lenses to project the image from behind onto the viewing screen. This enables the displayed picture to be significantly larger, up to 70 inches or more. This technique usually offers the best value (picture size vs. cost).

Front Projection TV (FPTV):
this is like a movie theater. The image is projected forward, to an external screen. But like a movie theater, a very dark room is required because the screen will reflect any light in the room. This technique is usually more expensive than rear-projection, but the footprint (the area consumed by the equipment) of the system is smaller.

TV Display Techniques:

CRT (Cathode Ray Tube):
The established standard for television displays; good value, picture quality. The maximum size of the screen is smaller with the technique. The technology is still a good choice where a smaller picture is desired, and bulkiness is not a concern.

Liquid Crystal Display (LCD):
Thin design, but has problems displaying images in motion (sports), the images tend to streak. These projectors usually contain three separate LCD glass panels, one for red, green, and blue components of the image being projected. As the non-colored light passes through the LCD panels, individual picture elements (pixels) can be opened to allow light to pass or closed to block the light. This produces the image that is projected onto the screen.

Historically, LCD sets have had a problem with visible pixelation (screendoor effect). It looks like you are viewing the image through a screendoor. This is less apparent on newer sets with higher screen resolutions.

Pros:

Better color saturation, more rich and vibrant

Better sharper image, important for text

More energy efficient

Cons:

Poor black levels and contrast

Problems displaying images in motion (sports)

LCD panels (mainly in the blue channel) can degrade, causing shifts in color balance

Visible pixelation (screendoor effect)

Liquid Crystal on Silicon (LCoS):
A type of LCD Technology, LCOS uses liquid crystal rather than mirrors to project (usually rear projection) an image on the screen. LCOS is a good value compared to plasma and LCD sets, but expensive when compared to all other rear projection television technologies such as DLP. This technique uses a chip like a DLP (see below) set does, but the chip is coated with liquid crystal, which reflects the image seen on the screen. LCOS based systems allow for higher screen resolution than an LCD display or a plasma display.

Pros:

Sharp, vivid colors, and deep black levels

It does not slowly change over time as a plasma set does

Cons:

Dead pixels usually happen because the technology is partially reflective

High Maintenance Cost: LCoS requires frequent bulb changing requirements (anywhere from 6,000 to 8,000 hours, about 3-4 years with normal usage) versus 50,000 or more for most LCD or plasma screens. A replacement bulb will cost about $400

Reproducibility: Image quality can vary greatly from machine to machine

Digital Light Processor (DLP):
The DLP is a Texas Instruments product that is manufactured in Korea. It uses a chip with many mirrors (can be more than one million mirrors on a chip of about one square inch) that can be mechanically steered to reflect the correct color. This technology offers excellent display, at a moderate cost.

In the best DLP projectors, like the ones in use at your local movie theater, there are three separate mirror chips, one each for the red, green, and blue channels. However, in the DLP projectors marketed for the masses, there is only one chip. In these sets, to define color, there is a color wheel that consists of red, green, blue filters. This wheel spins between the lamp and the DLP chip and alternates the color of the light hitting the chip.

The spinning color wheel used to project the image can produce a problem on the screen known as the rainbow effect, which is colors separating out in distinct red, green, and blue. At any given point of time, the image on the screen is either red, or green, or blue, and the technique relies upon your eyes not being able to detect the rapid changes from one to the other. However, not only can some people see the colors separate, but the rapid sequencing of color may be responsible for reported cases of eye strain and headaches. But the vast majority of the people cannot detect the rainbow effect.

Newer sets have the color wheel rotation speed doubled. Also, newer sets utilize a six-segment color wheel (instead of a 3 segment) that has two sequences of red, green, and blue. Because the wheel is at double speed, and because the red, green, and blue are seen twice in every rotation, the effect is a quadrupling of the rotation speed. This eliminated the visibility of rainbows for most of the people who previously saw the effect.

Pros:

Small package size

High contrast image with deep black levels

Good value

Cons:

Less bright images

Rainbow effect

High Maintenance Cost: DLP requires frequent bulb changing requirements (anywhere from 6,000 to 8,000 hours, about 3-4 years with normal usage) versus 50,000 or more for most LCD or plasma screens. A replacement bulb will cost about $300-$400. Samsung is using LED illumination instead of lamps. The LED should not have to be replaced.

Plasma Display:
Thin design, high contrast ratings, Size up to 60 inches or more; some display limitations: costly, older systems had a high burn-in risk (over time, a memory of what was projected was retained); This could pose a problem for those who like to play video games or watch taped movies. If you put the game or tape on pause for too long, this could burn an image into your screen.

Pros:

Exceptional picture quality: It can produce up to 8.6 billion colors, an accurate color reproduction and wide viewing angles

Large screen sizes: Some Plasma TV units are now manufactured in screen sizes that can span up to 100 inches

Lifetime: Plasma TVs are also known for their extended lifespan capacity of approximately 60,000 hours and great contrast (deep blacks)

Less Expensive than LCD

Cons:

The displays are very bulky, heavy, and fragile

Burn-in

Slowly degrades over time

Energy inefficient

Standards:

NTSC Analog TV or Standard Definition TV (SDTV):
The current system that is being phased out (National Television Systems Committee).

EDTV (Enhanced Digital TV): basically high-end Standard Definition TV:
While these sets may be better than standard sets, the picture quality is not equal to HDTV. Technically, there is little difference between an SDTV and an EDTV (except for the higher price).

ATSC Digital TV:
This is the new system (Advanced Television Systems Committee), which by the way; is not necessarily.

HDTV:
is digital TV where the image is a wide-screen picture with many times much detail than is contained in current analog television pictures. Most consumers will see a huge improvement in image quality. HDTV has a better quality image than SDTV because it has a greater number of lines of resolution. The image is two to five times sharper because the gaps between the scan lines are narrower.

Summary

Any of the four technologies can be a good choice. The competition is intense, and all of the technologies will continue to improve. Buying a TV will never again be as simple as it was before HDTV, but the benefits are worth the headaches.

Information about the Author:

Brian Bradshaw is a Certified Technical Specialist (InfoComm CTS). Areas of expertise include Video, HDTV, Audio, Computation, Satellite, and Communications. He has a AudioVisual Technology business in Plano, Texas (Dallas). More information can be found at his Website (click here)

Technology Articles: http://www.article-buzz.com

Print This Article
Add To Favorites
Email to Friends
Get Re-print Code