June 13, 2006
HDTV - DLP TV Explained
Conventional TVs (CRTs) project electrons in a series of lines across the back of the screen, usually by 'painting' every other line, then starting over and illuminating the other half.
DLPs (Digital Light Processing) have no electron gun. Instead, the image is formed by shining tiny lights onto a million or more miniature mirrors that tilt 'on' or 'off' a thousand times per second. The light is passed through a color wheel, filtering it into red, green and blue then shone onto the DLP chip.
The DLP chip at the heart of the system is a proprietary technology invented by TI engineer Dr. Larry Hornbeck in 1987 and marketed by Texas Instruments starting in 1996.
All color combinations are produced from these three. The rapid 'switching' has the potential to cause a kind of visual 'flutter', but most good sets no longer suffer from that drawback. The signals are then converted into an image projected onto the rear of the screen.
DLPs paint the screen in one of two different ways - progressive or interlaced. 'Interlacing' consists of drawing every other line (like CRTs), 'progressive' scanning hits them all in one pass. The result is two different specifications for DLPs – p or i, following the number of lines making up the screen, 720 or 1,080. There are 480p sets, but they're not recommended for anyone willing to spend the money for an HDTV set.
Add to that already complicated picture the variation in resolution created by differing numbers of pixels. For example, 1366 x 768 resolution means: 1,366 times 768 = 1,049,088 pixels, 1920 x 1080 = 2,072,600. More pixels, better resolution (all other things being equal, which they rarely are).
The major TV networks already show many programs in 1080i format and 1080p is anticipated in the near future.
The final major element determining quality is the ability of the set to 'convert up or down'. Most sources (DVDs, commercial broadcasts, etc) don't fit neatly into the numbers shown above. For example, films are shown in 24 frames per second, video in 30 frames per second.
Some electronic wizardry has to be performed to get them to match without the picture looking odd. How well the set does that - and several other kinds of internal - conversion has a large effect on the resulting visual quality.
DLP HDTVs can produce a crisp, realistic looking image with no motion blur and excellent color fidelity. Gamers, sports fans and anyone who wants an unbelievably sharp picture should test view some sets. They are often less costly than other HDTV sets, such as LCD and plasmas, and (with the micro-projector type) don't suffer from burn-in problems.
Contrast ratios for a quality set are in the range of 12000:1, putting it at the top of the list for this important criterion. Unlike some plasmas and LCD sets, there's no 'screen door' effect, thanks to the mirrors being spaced less than a micron apart.
Digital Light Processing is a rear-projection technology that - in most commercial sets today - ranges in size from 40" to 80". They frequently have replaceable lamps, with a lamp life of 2,000-3,000 hours or more.
The systems can theoretically reproduce many millions more colors than the human eye can discern, and over a thousand shades of gray. The result is excellent color and shading realism in a large (near) flat-panel display.
Posted by HDTV at 04:30 PM | Comments (0)
