Let’s see how they work, any advantages and disadvantages.
Give you a brief concept of HDTV technology.
CRT
How it works?
Direct view: In standard TV design, a single CRT uses three electron guns to excite RGB phosphors.
Rear projection: Three small CRTs generate an RGB image, which mirrors enlarge and project onto a screen.
Advantages
Direct view: Relatively low cost; deep black levels and excellent contrast ratios; long life.
Rear projection: Excellent price/performance ratio; lowest cost Deep blacks, excellent contrast ratios, multiple scan rates.
Disadvantages
Direct view:Heavy and bulky. Picture not as sharp; horizontal HD resolution much less than the 1,920 lines in true 1080L.
Rear projection: Needs calibration for optimal quality. Beam convergence can be a problem. Not as bright; limited viewing angles.
DLP
How it works?
Front projection: A lamp shines through a spinning RGB color wheel. Colors sequentially hit a Digital Micromirror Device, and the image is projected onto any display surface.
Rear projection: As above, a lamp shines through a color wheel onto a DMD, made of numerous tiny mirrors that steer light onto or away from a screen.
Advantages
Front projection: Small, lightweight design scales well. Bright image; excellent picture geometry. Some DLPs target 720p resolution; 800-by-600 to 1,280-by-1,024 is available.
Rear projection: Thin and lightweight Very bright, sharp images. Good viewing angles side to side. Reasonable cost
Disadvantages
Front projection: Mounting the projector can be a problem. The color wheel can produce a rainbow effect, dithering, lack of shadow details. Pricey bulbs; possible stuck mirrors.
Rear projection: The color wheel can produce a rainbow effect, dithering, lack of shadow details. Expensive bulbs with limited life. Possible stuck mirrors.
LCD
How it works?
Direct view: Liquid crystals are sandwiched between two glass and two electrode plates. A current twists selected regions of crystals to block or pass light.
Front projection: A high-intensity lamp shines light through three transmissive LCD microdisplay panels (RGB), and the image is projected onto any display surface.
Rear projection: As above, except that optics steer the light to a display screen.
Advantages
Direct view: Fairly lightweight. Brighter than plasma; some designs are nearly photographic with HD content and head-on viewing. Excellent picture geometry.
Front projection: Small, lightweight design scales well. Bright image; excellent picture geometry. Some target 72Op reso lution; 800-by-600 to 1,280-by-1,024 is available, too.
Rear projection:Thin and lightweight Excellent picture geometry. Reasonable cost.
Disadvantages
Direct view: Costly, requiring an active-matrix substrate with at least one transistor for every subpixel. Possible dead pixels and viewing-angle limitations.
Front projection: Mounting the projector can be a problem. Possible dead pixels initially or over time; weak black levels. Expensive bulbs with limited life. Pixel structure is visible up close.
Rear projection:Possible dead pixels initially or over time; black levels not very black; limited contrast ratio. Pixel structure is visible at close range (screen-door effect).
LCoS
How it works?
Rear projection: Liquid crystals are layered atop a reflective metal. Light shines on the chip; a voltage twists selected liquid crystals, and light reflects off the metal. Optics enlarge the image onto a screen.
Advantages
Barely visible pixel structure even at close range. Natural-loo king images with good color saturation.
Disadvantages
Possible dead pixels initially or over time. Black levels could be blacker; limited contrast ratio. Expensive bulbs with limited life.
Plasma
How it works?
Direct view: Millions of individual cells filled with gas emit UV light when excited by an electrical charge. The strikes RGB phosphors, which emit visible light
Advantages
Thin, flat display. Fairly lightweight. Excellent color saturation and picture geometry. Wide viewing light angles; very large sizes.
Disadvantages
Costly; can suffer from dead pixels and burn-in; limited contrast. Glass may cause image degradation under direct lighting. Brightness decreases over time.
