1080p: Time For a Reality Check!

[dkennedy]

1080p: Time For a Reality Check!

July 1, 2005

by Peter H. Putman, CTS HDTV Expert

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…

Copyright ©2005 Peter Putman / Roam Consulting Inc.
All electronic and mechanical reproduction rights are reserved.

[dkennedy]

The New Kid On The Block <Part 1 of 2>

August 11, 2005

By Ed Milbourn, HDTV Magazine

Yes, there is a new kid on the HDTV block. And it is (drum roll) -1080p. 1080p is one of those incremental improvements in HDTV to which I have been referring to in my previous articles. 1080p, of course, means 1080 horizontal lines scanned one after the other, or progressively. This is opposed to 1080i that denotes 1080 lines scanned in an interlaced fashion, with the odd number of lines scanned initially and the even number of lines then scanned and positioned, or "interlaced," between the odd lines.

So, is 1080p better than 1080i? Is it better than 720p? The answer to both of these questions is yes, it can be. But alone is it enough to blow up your skirt and entice you to fork out the initial added premium? Probably not. Allow me to explain:

Usually, "P" is better than "I," and more lines are better than fewer lines. Understand that progressive scan does not improve the picture resolution. [OK, the purists will site the so-called "Interlace Factor," that causes a loss of vertical resolution due to the interlace scanning structure. But this effect is virtually invisible at normal viewing distances. So, bug off! Progressive scan does, however, eliminate temporal artifacts, such as the "shimmer" that occurs when interlaced images are panned vertically. The progressively scanned image also appears "smoother," more "film-like," due to the virtual elimination of any visible scanning line structure. However, there is a small fly in the ointment.

Historically, there were three basic reasons an interlaced scanning scheme was adopted for the 525-line/30 frames per second (fps) U.S. TV video format. These were: the minimization of "flicker," which is objectionable at 30 sequential frames per second; the minimization of the video bandwidth required by doubling the amount of time to construct each frame; and the easier horizontal deflection design requirements by operating at 15.75Khz instead of 31.50Khz. These factors reflected the state-of-the-art when the standard was codified in 1941.

Today, progressive scanning at 60fps eliminates the flicker problem, and deflection (or digital device switching) speeds present no real problem, but broadcast bandwidth constraints remain. This is why of the 18 different video formats specified by the Advanced Television System Committee (ATSC)' 1080p at 60fbs is not supported, but 1080p at 30fps is supported. It would take twice the bandwidth to transmit 1080p at 60fps. 720p at 60fps can be supported because the reduced number of pixels-per-frame is within the bandwidth constraints of the ATSC system.

So, unless somebody comes up with a bunch more spectrum, or ATSC scraps MGEG2 for MGEG4 (not likely), we will not see 1080p at 60fps transmitted. Of course, it is possible to see 1080p at 30fps transmitted (assuming the camera chain can handle it), or authored for DVD and/or video games. At some point, thanks to MPEG4, many of these sources, except broadcast video, may offer a full 1080p format at 60fps. In the meantime it is up to the 1080p display system to deal with the flicker problem presented by 1080p at 30fps. And this is the point at which we must be very careful with 1080p.

[dkennedy]

The New Kid On The Block <Part 2 of 2>

August 11, 2005

By Ed Milbourn, HDTV Magazine

It is always optimum to reproduce video material in the same format in which it is originated. Obviously, the optimum production and delivery format for 1080p is with a 60 per second frame rate. Although some material will be produced and delivered at 1080p 60fps, such as some future HD DVD's and games, most of the HD material that will be delivered - in the foreseeable future - in the ATSC standards of 1080i 30fps or 1080p 30fps. Therefore, for the most part, the display system must convert the 1080p 30fps material to 60fps. This means the display system must incorporate some sort of up-conversion (or line interpellation) process in order to add another 1/60th of a second's worth of 1080 lines to emulate 60fps.

Although interpolation algorithms have greatly improved in the past few years, none of them are perfect. The most common problem of badly design up-converters is the introduction of horizontal movement artifacts - the dreaded motion smear. Yuck!

The newer up-converter algorithms have sufficient sophistication, memory and bandwidth to produce extremely accurate interpolated lines.

Another dimension of up-conversion is the capability of the system to handle other than primary scanning rates. In other words, how well it processes and displays native 480i, 480p and 720p material. The ability of digitally switched displays - such as DLP, LCoS, Plasma etc., - can have a significant advantage over CRT's relative to scan conversion. This is because the CRT's deflection is most economically operated at a single rate regardless of the signal's scanning format while digital display rates can be easily switched.

So, that brings us to the final question: does a 1080p image display a noticeably higher detailed image that 720p under normal viewing conditions? Not really. It so happens that when a one mega-pixel or greater image is viewed from a distance of three times the picture height or greater, it is almost impossible to discern any difference in picture resolution as the pixel count increases. This is because at those viewing distances, the human eye/brain system's perception of resolution becomes essentially "flat" at above one mega-pixel. It is even flatter if the image is in motion, as the brain requires only 1/3rd of the static pixel count to produce the same perception of resolution. Now, if a static image is viewed at closer than three times the picture height - such as in some commercial (e.g. "Computer Aided Design"), medical, text-intensive and/or web-page applications where the image must be studied - then certainly the greater the pixel count, the greater the perceived resolution. As one anonymous engineer remarked in the early days of the development of television, "After all, television doesn't have to work; it only has to look like it does."

In actuality, at normal viewing distances, the higher picture quality that may be perceived by the new 1080p displays is due mostly by improvements in video signal processing and imaging component performance. Performance parameter improvements such as in brightness, contrast, adaptable aperture correction, noise reduction et. al., added to imaging component improvements in lenses, screens and imagers have a much greater impact on picture performance than 1080p itself. But 1080p is certainly an advance in the right direction. Like any kid, with any kind of luck, it will grow and develop, and add to the increasingly improving quality of HDTV. It will only get better.

[zekmoe]

This whole article smarts of Po-Boy sour grapes. It's like the same reasoning that consmer reports used when they lied about the sounds of all CD players being the same, when in fact they are glaringly different. Look at the image, the features, and the cost, and decide for yourself.