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View Full Version : 1080P Time for a Reality Check!



thylantyr
04-19-2006, 05:02 PM
http://www.hdtvexpert.com/pages_b/reality.html

PETER PUTMAN, CTS
Thinking about buying a new 1080p rear-projection TV, front projector, or LCD TV? You might want to put your credit card back in your wallet after you read this.

It’s obvious that the buzzword in consumer TV technology this year is “1080p”. Several manufacturers are showing and shipping 1080p DLP and LCoS rear-projection TVs. We’ve seen RPTVs and front projectors with 1920x1080 polysilicon LCD panels at CESA, NAB, and InfoComm. And the trickle of large LCD TVs and monitors with 1920x1080 resolution is turning into a flood.

To get your attention, marketers are referring to 1080p as “full spec” HD or “true” HD, a phrase also used by more than one HD veteran in the broadcast industry. We’re hearing about “1080p content” coming out of Hollywood, from broadcasters, from cable systems, and from direct broadcast satellite services.

The budding format war between Blu-ray and HD DVD for the next generation of high definition DVD players promises the same thing — 1080p content at high bit rates, finally realizing the full potential of HDTV.

STOP!

Enough of this nonsense. It’s time to set the record straight, to clear up the air about what 1080p is and isn’t.

First off, there is no 1080p HDTV transmission format. There is a 1080p/24 production format in wide use for prime time TV shows and some feature films. But these programs must be converted to 1080i/30 (that’s interlaced, not progressive scan) before airing on any terrestrial, satellite, or cable TV network.

What’s that, you say? Those 1080p/24 could be broadcast as a digital signal? That’s true, except that none of the consumer HDTV sets out there would support the non-standard horizontal scan rate required. And you sure wouldn’t want to watch 24Hz video for any length of time; the flicker would drive you crazy after a few seconds.

No, you’d need to have your TV refresh images at either a 2x (48Hz) or 3x (72Hz) frame rate, neither of which is supported by most HDTVs. If the HDTV has a computer (PC) input, that might work. But if you are receiving the signals off-air or using a DVI HDCP or HDMI connection, you’ll be outta luck.

What about live HDTV? That is captured, edited, and broadcast as 1080i/30. No exceptions. At present, there are no off-the-shelf broadcast cameras that can handle 1080p/60, a true progressive format with fast picture refresh rates. It’s just too much digital data to handle and requires way too much bandwidth or severe MPEG compression. (Consider that uncompressed 1920x1080i requires about 1.3 gigabits per second to move around. 1080p/60 would double that data rate.)

How about Blu-ray and HD-DVD? If either format is used to store and play back live HD content, it will have to be 1920x1080i (interlaced again) to be compatible with the bulk of consumer TVs. And any progressive-scan content will also have to be interlaced for viewing on the majority of HDTV sets.

Here’s why. To cut manufacturing costs, most HDTV sets run their horizontal scan at a constant 33.8 kHz, which is what’s needed for 1080i (or 540p). 1080p scans pictures twice as fast at 67.6 kHz. But most of today’s HDTVs don’t even support external 720p signal sources, which requires a 44.9 kHz higher scan rate.

In the consumer TV business today, it’s all about cutting prices and moving as many sets as possible through big distribution channels. So, I ask you: Why would HDTV manufacturers want to add to the price of their sets by supporting 1080p/60, a format that no HDTV network uses?

Here’s something else to think about. The leading manufacturer of LCD TVs does not support the playback of 1080p content on its own 1920x1080 products, whether the signal is in the YPbPr component or RGB format. Only the industrial monitor version of this same LCD HDTV can accept a 1920x1080p RGB signal.

Now, don’t blame HDTV manufacturers for this oversight. They are only supporting the 1080 format in actual use, 1920x1080i, a legacy digital format that has its roots in the older Japanese MUSE analog HDTV format of the 1980s. That’s one big reason that 1080i has remained as a production and transmission format.

It gets worse. All kinds of compromises are made in the acquisition, production, and transmission of 1080i content, from cameras with less than full resolution in their sensors and reduced sampling of luminance and chrominance to excessive MPEG compression of the signal as it travels from antenna, dish, or cable to your TV.

But that’s not all. To show a 1080i signal, many consumer HDTVs do the conversion from interlaced to progressive scan using an economical, “quickie” approach that throws away half the vertical resolution in the 1080i image. The resulting 540p image is fine for CRT HDTV sets, which can’t show all that much detail to begin with. And 540p is not too difficult to scale up to 720p.

But a 540p signal played back on a 1080p display doesn’t cut the mustard. You will quickly see the loss in resolution, not to mention motion and interline picture artifacts. Add to that other garbage such as mosquito noise and macroblocking, and you’ve got a pretty sorry-looking signal on your new big screen 1080p TV.

Oops! Almost forgot, that same 1080p TV may not have full horizontal pixel resolution if it uses 1080p DLP technology. The digital micromirror devices used in these TVs have 960x1080 native resolution, using a technique known as “wobbulation” to refresh two sets of 960 horizontal pixels at high speed, providing the 1920x1080 image. It’s a “cost thing” again. (Let’s hope these sets don’t employ the 540p conversion trick as well!

To summarize: There are no fast refresh (30Hz or 60Hz) 1080p production or transmission formats in use, nor are there any looming in the near future — even on the new HD-DVD and Blu-ray formats. The bandwidth is barely there for 1080i channels, and it’s probably just as well, because most TVs wouldn’t support 1080p/60 anyway — they’d just convert those signals to 1080i or 540p before you saw them.

The 1280x720 progressive-scan HDTV format, which can be captured at full resolution using existing broadcast cameras and survives MPEG-2 compression better than 1080i, doesn’t make it to most HDTV screens without first being altered to 1080i or 540p in a set-top box or in the HDTV set itself. So what chance would a 1080p signal have?

Still think you’ve just gotta have that new 1080p RPTV? Wait until you see what standard definition analog TV and digital cable look like on it…

Vincent9515
04-19-2006, 05:09 PM
Haha. :D

Nice to see you on here with your usual good threads.

springy101
04-19-2006, 08:29 PM
so according to this is 720p the best or 1080i?