Viewing Distance

[Guest]

Some Science, some art.

I thought the comment about the right amount of cream and sugar in the coffee was close to the mark to how many see this issue except for the extensive science that went into determining the viewing distance and the experience it provides, and from that derived the technical specifications for HDTV.

HDTV was invented -- or specified -- to accomplish a new viewing experience.

Without a new experience, it was reasoned, there is not a lot to sell. So, it was determined whatthat experience would or could be by using a very complex and sophisticated evaluation scheme where people were hooked up to all kinds of devices for reading the emotional and physical changes going on in the viewer under different viewing conditions.

It was determined after exhaustive tests that in order to have a new and more realistic experience both central and peripheral vision had to be stimulated.

They (peripheral and central)operate together but offer to the brain different stimuli in order to identify different conditions.

The central portion of the human visual system arcs about 10 degrees--a field of vision of ten degrees. This "channel," as many scientist have called it in the papers given on this subject, is best for detail, but due to its greater persistence of vision (retention of the image), it has less-value in detecting motion.

All of the compression algorithms take the human visual responses into account. The peripheral vision is less sensitive to detail and much more sensitive to motion. The two, when combined (as in real life), offer the sense of reality that is being rightly sold to you as HDTV.


So, the decision was handed down by science that if you want a new experience for television you have to abandon the 10 degree field of view that is typical of the NTSC viewer (who has made that a standard distance in order to hide from sight the artifact of this old lower performing system) and expand that to a 30 degree field of view with a greater bandwidth to drive it, which science said was essential to a achieving new experience--"without noticeable artifacts, such as scanning lines or color blurring...or anything else."

Then the question of how much bandwidth would that take was asked by the electronics developers. Was that doable?

Indeed, you could take this science report and say, "Well if 30 degree field of view is good, how about 60 degree field of vision? Would that not be better? Why limit ourselves to 30 degrees?"

It was also determined that by extending past the 30 degree field of vision you didn't gain so much more in the over-all experience of heightened reality as you have in 30 degree vision, and you would add unreasonable bandwidth cost for whatever small gain there could be. (As bandwidth becomes less an issue it will cause the 30 degree to extend beyond. We all know that is a cinema in the round, such as was found at Disneyland for years, there is something still to be gained, but at what price?)

What determined the parameters for HDTV?

Following the science report the question was: How much bandwidth would be required to display such an image that would be artifact-free at the 30 degree field of vision?

The answer was: "It would take 30 MHz, which translated to two million pixels, or, as the CCIR put it, a system having at least 1000 scanning lines running from top to bottom and 2000 sampling points across each line. We ended up after much international hassle with 1080 lines by 1920 samples--very close to the original dictates of science.

Coloremitry is taken into account, but one could have a field of vision of 30 degrees in black and white. So, opening the color gamut was more opportunistic than integral to the concept of HDTV.

All of the compression algorithms are built around the biological facts of the human visual system. Our system does not have perfect geometry nor perfect linearity, or is always identical to individuals, but it is statistically identical enough to make this product function as invisaged for 100% of the public. Much has been researched about it.

So, you can sit anywhere you like but the entire reason for HDTV was and is built on the fact that you should be able to sit at 3 times the height of the 16:9 picture, which then yields this 30 degree field of vision, which provides you, the viewer, with an heightened sense of reality--emersion. You can defeat the purpose of HDTV and sit in the next county with binoculars if you like. But don't complain if it doesn't blow you socks off. The biggest and most horrible fraud ever perpetrated on a television audience is a 16:9 screen that only has 480p capacity. You will never be comfortable sitting at the prescribed distance of 3 PHs since it will still have visual artifacts to distract you from the desired experience. One of the danger points being treaded upon by the 720 p camp is that at 3 times height it can look a tad soft, so you pull back out of the 30 degree field of vision zone to achieve acuity. You end with a clear picture then, but if carried too far you lost the HDTV experience.

When people talk about 480p widescreen as being the right choice (always a bandwidth driven argument)they just double me up in laughter. It's the right choice for 4:3 ten degree field of vision viewing and has nothing to do with the HDTV experience. Promoting widecreen 480p is the perfect perscription for scraping the whole thing and sticking with what we have. There are plenty of "fix ups" in NTSC which Yves Faroudja has demonstrated for years.

One of the things intriguing to me about the LCOS set is that it is faithful in reproducing all of the 30 MHz expanded uncompressed 1080i X 1920 image. If that holds true past manufacturing compromises then we have the real experience that was designed into the mission and a reference to test everyone's signals being tossed at us. Displays that are 480p native, such as these flat panels coming in from China for Gateway and others, who claim to be HD-ready should be convicted and do a little time in the cooler for public fraud. You can sit and smile and talk to your friends about the wonderful new modern widescreen that doesn't do a damn thing to change your real viewing experience except for better colorimetry, which is a bonus handed down to us from earlier digital work.

It's a good thing if you do it right.

Dale Cripps

[Guest]

The viewing ditstance argument is an ongoing issue up for much debate. I work part-time (for fun and discounts) at Best Buy in the Television section and get asked this question many times by various customers. I equate it to preference rather than the scientific method of screen size related to distance. Most people really don't understand, or care for that matter, about a complicated formula for calculating it. When I go to movie at the local multiplex, I often times (if I can cajole my wife into it) sit third row center. Personally, I like the screen to overwhelm me. I prefer to be right in the middle of all the action, likewise for the home viewing experience. I sit 8 feet back on a 57" screen in my living room and still regret not buying a 65". Bigger the better. I also realize others (including my wife) prefer a much more subtle viewing experience. So ask yourself the same question: Where do you prefer to sit at a movie theater? Same goes for a sporting event. The closer you are to the action, the more memorable the experience. That is how to decide on which screen size you should buy in my opinion.

(unknown)

[Guest]

Dale,

Thank you for that awesome explanation. Another facet of using the correct viewing distance is the ability to critically judge quality. None of the broadcast HDTV in the Atlanta area is meeting 3 picture heights due to pixelation and contouring yet it was designed to meet this critical viewing distance. So far, I am one of the few complaining and that does not bode well since it is upon us, the consumers, to determine the level of quality for all.

Ultimately HDTV Magazine and this forum is all about what HDTV can aspire to and not the minimum requirements to get a DTV or HDTV picture in your home. We hope to turn many casual viewers into videophiles for the common good.

Joe Kane

[Guest]

Sorry for the late shot here, but I just found out about this forum.

One way to get people to understand that you gotta get closer to the screen to get the HD "wow" is to jawbone the consumer electronics industry.

I have yet to see an ad for an HD set -- particularly a thin screen -- in which the people or the seating are close enough to the screen. The ad designers must think of this stuff as furniture, because you see the sets placed above fireplaces, six feet up a wall, across the room from the seating, etc. etc.

Many people take their cues from ads and will end up putting their sets in the same kinds of configuration that they see in the glossies.

Can't someone talk to these people? It is certainly not in the consumer electronics industry's self-interest if someone shells out $10K or more for a screen that ends up as a talking wall hanging. Would that person feel like he got his money's worth from HD and would he then tell his friends about the "wow"?

What do you think?

David Turkheimer

[Guest]

I agree with most, if not all your points, especially the 1080 vs 480. One factor not inlcuded in this analysis of a "New Viewing Experience" is the change in the way the HD content is created. For example, in HD sports programming, I find that directors are using more 'wide angle shots' to take advatage of 16x9 and showing us an extended field of play. This creates a new viewing experience. However, it also makes me feel like I am further away from the action, and I often find myself cropping the picture to 'zoom in' on the central part of the action. This 'art' still is evolving and I guess is also very depended on individual preferences.

BobH NYC

[AlanBrown]

Thank you Dale and Richard for the increased clarity in this continual debate. Maybe some day I'll understand the psychology better behind the resistance in some people to well-researched and proven standards. Rather than a curiosity in understanding the standards better, I keep hearing folks recommend the, "if it feels good, do it," method of problem solving.

This "syndrome" may be at the root of some of the advertising issues mentioned previously. There ever seems to be a consistent disconnect between the marketing and engineering departments of manufacturers.

If everyone knew intuitively what worked best for them, we wouldn't need scientists, engineers, universities, research, standards, laws, rules, etc. There will never be an end to the importance of speaking up for accuracy, precision and technical standards in a technology-based industry and market. Leaders and spokesmen like Joe Kane, Dale, the ISF, etc. have made a difference in bringing us greater enjoyment of the available technology. Consumers understand what's correct in video more often these days, and are helping to hold manufacturers' feet to the fire. There is still much to do.

Best regards and beautiful pictures,
Alan Brown, President
CinemaQuest, Inc.
www.cinemaquestinc.com

"Advancing the art and science of electronic imaging"

[Hugh]

After doing a fair amount of research on this subject and initially thinking it was a matter of personal preference, I found out that there is a reason for the distance being 1.63 times the diagonal or 3.1 times the height for HD viewing and it has to do with the viewing angle of 30 degrees. You can find confirmation of these figures in the book "Digital Video and HDTV" by Charles Poynton. You can also go to the following online site:

http://www.myhometheater.homestead.com/ ... chor_13194

The above site has been mentioned in a previous post. Granted, some people will not want to sit at this specific distance but if you want the best experience this is where you want to sit.