HDTV Aspect Ratio (1 Viewer)

[George>K]

I have a question regarding the aspect ration of HDTV. It was always my understanding that HDTV was native 16:9. Here's why I am confused. I have a Pioneer Elite RPTV and Sony DVD player. I spent a fair bit of time understanding exactly what each screen mode on the TV does. The mode called "Full" would stretch the frame horizontally to fill the 16:9 screen. This was the appropriate mode for any widescreen anamorphic DVD. The other modes zoomed the frame for non-anamorphic letterboxed frames that were native 4:3, so when zoomed, filled the 16:9 screen nicely. And of course, the Natural Wide mode which does a bit of zomming and a bit of stretching for a best fit for NTSC 4:3 TV frames.

Now the confusion. I recently bought an HDTV decoder for local cable. When I have a true HDTV signal feedign the TV via component input, the TV automatically locks to Full mode (I can't change). At first, this seemd to make sense. But when I thought about it, since Full mode stretchs the frame, is it also stretching this HDTV frame? I thought HDTV was native 16:9 so all the TV would have to do is display it, with no stretching or zooming. What gives??

Thanks.

 

[Darryl_B]

It is a design flaw in your TV that it "locks" in full mode when fed an HDTV or progressive signal. Many older HDTV sets were erroneously built this way. Pioneer stuck with the design flaw longer than most other manufacturers...and I'm still not sure whether they eventually stopped it with their sets or not.

 

[Scott Merryfield]

Many HD-ready sets will also "lock into FULL mode" when presented a 480p video signal from a progressive scan DVD player. Even more TV's do this when presented a 1080i or 720p signal.

My 3 year old Toshiba 56H80's aspect ratio controls are available with a 480p signal, but the set locks into full mode with a 1080i video signal.

 

[Brian L]

It is a design flaw in your TV that it "locks" in full mode when fed an HDTV or progressive signal.

No quite.

Full for HD is not the same as Full for non-HD.

If you are receiving a true HD signal, which by definition is a 16:9 frame, your TV does not do any stretching; it simply displays the signal as it is received.

Are you seeing any geometric distortion when you are getting an HD signal? I would think not.

I have a non-Elite Pioneer 533, which only locks into full when it gets a true 1080i signal. Anything else allows full aspect ration control. As you said, full mode for non-HD content is the correct mode for anamorphic DVD.

Things can get muddy depending on how your local stations are broadcasting.

My local ABC affiliate sends on SD content windowboxed in a 16:9 frame. Ny CBS affiliate does a zoom of there CD stuff, and then sends that out in a 16:9 frame. But they both pass along true HD properly.

Rest assured, when you are getting true HD content (16:9, 1080i) your set is correct to lock into Full mode.

BGL

 

[Don Munsil]

"Full" is not a stretch mode. "Full" is a normal 16x9 mode. HDTV is 16x9, as is so-called "anamorphic" DVD. They're both 16x9, so the TV needs to be in 16x9 mode. Q.E.D.

The other modes, like "natural wide" (which gets my vote for 'least accurate description') are different ways of converting 4x3 content to 16x9. Full is the only "native" mode of the TV that applies no processing to the signal.

People are so used to video signals being 4x3 that they came up with the term "anamorphic" to describe 16x9 video. It's a terrible term, because 16x9 video is not at all anamorphic. It's just 16x9. Don't think of a 16x9 DVD as being a 16x9 image "squished" into a 4x3 frame, which your TV then has to "stretch" to make it look right. It's a native 16x9 image, which is recorded on the disc as a 16x9 image, and then displayed by your TV as a 16x9 image. No stretching or squishing is necessary.

Does that help?

Don

 

[Don_Berg]

The full frame for HD or anamorphic DVD is 16:9 so its not stretched in FULL mode for these sources, its designed for a 16:9 display and should fill it. The stretching (its in reality scaling) is the other modes for displaying 4:3 material on a 16:9 display. Everything is scaled anyway, so don't worry about it - just use the best scaling electronics.

 

[George>K]

Actually, Full is a stretch mode when the source is an anamorphic DVD. And anamorphic is more than a catchy phrase for widescreen; it is a specific way to delivery the wide aspect ratio frame. The Digital Bits website has an excellent technical explanation of Anamorphic that I would encourage you to review. I won't repeat it here, but basically, since DVD-Video is based on the NTSC standard, which is 4:3, the frame can't possibly exist in native 16:9 on a DVD. Thus, the wide aspect ratio needs to be delivered via the 4:3 frame, thru either letterboxing or horizonatlly squishing (anamorphic or sometimes called "enhanced for widescreen TV's"). The bottom line is resolution and picture quality. Letterboxing wastes lines of resolution that get cut off; anamorphic doesn't. Check out the Digital Bits site.

So, I guess the TV must be able to tell if the source is anamorphic or not and whether or not to stretch. I know it will stretch a non-HD signal in Full Mode because when I play std. cable, which is NTSC 4:3, the frame is stretched horizontally and distorted. My only question was, does Full Mode always stretch or only when a non-HD source is playing. If it always stretches, then the HD signal must be squished and is being delivered 4:3, but this was not what I understood to be the new ATSC HD standard. So, I guess the TV knows. I was just wondering if someone knew this for sure, not through deduction like I have done.

Anyway, thanks for the feedback. Cheers.

 

[Jeff Gatie]

The HD signal is not squished, it is designed to be displayed full width in a 16:9 ratio, which is what the "Full" mode is. "Full" is just what it sounds like - full width of the 16:9 frame. An anamorphic dvd is designed to be the full width of a 16:9 frame, so you use "Full". A HD signal is native 16:9 (just like an anamorphic DVD) so you use "Full".

 

[George>K]

Anamorphic is definitely squeezed. Check out the Digital Bits website before you try to tell me any different. I can't post the url here, because this site won't let me. But please check it out. it's ".thedigitalbits.com"

 

[Jeff Gatie]

It's squeezed when you display it in a 4:3 aspect ratio, when I display it in 16:9, it's perfect. It is all relative to the size of the display. That's why there is no point to the question about "squeezed" or "stretched" HDTV. HDTV cannot be displayed in anything but a 16:9 ratio, so how can it be "squeezed" if it fits the 16:9 ratio perfectly.

 

[Don Munsil]

George, believe me, I know much more about this than thedigitalbits.com (not that I have anything against The Digital Bits; they do a great job). I'm a developer at Microsoft on the digital video team. I know the DVD spec inside and out - I have a copy on my desk. I am not guessing when I say the video on an "anamorphic" DVD is actually native 16x9 video. No squeezing of any kind is involved in the transfer of a 16x9 DVD. Thus the name "anamorphic" is not really correct. "16x9 enhanced" or "enhanced for 16x9 TVs" is a better designation, but really, "16x9" is all they need to say.

...OK, I just read the Digital Bits article, and it's basically fine about the benefits of 16x9 DVD, but it's wrong about the squeezing part, and it constantly refers to 16x9 DVD as anamorphic which is wrong. However, I'm inclined to cut them some slack because I'm pretty sure they wrote that article in the early days of DVD. Lots of movies were not being transferred in 16x9 format, and they wanted to tell people why they should be concerned. They perhaps didn't have all the details correct. You'll note, if you look down the list of phrases that different companies use to designate 16x9 DVDs, and "anamorphic" is only used by a few. Why? Because it's not anamorphic -- It's perfectly normal 16x9 video.

The idea that NTSC is always 4x3 is wrong, and has been wrong for probably at least 10 years. The spec for 16x9 NTSC video has been around for a long time. PAL has had a 16x9 version for even longer, and normal interlaced widescreen TVs are pretty common in Europe. We're behind the curve - they're broadcasting a wide variety of shows on regular TV channels in 16x9 format, and moreover they defined a widescreen signal that tells the TV what kind of video is coming in. NTSC has that as well, but no one seems to use it.

Don

 

[George>K]

Don,

I understand what you are saying, but there are still some observations that are not consistent with your explanation. Certainly I can buy that Digital Bits may be wrong. But, I have found several other references that all discuss the squeezing of the frame, and subsequent stretching by the display device. Furthermore, I have also seen references made about the enhanced DVD's having a flag to tell the display to stretch it. But, this is information from third parties, which I admit, one cannot 100% believe (no offense, Don, but you included). However, the one piece of hard evidence that I have is my own personal observation; when I display a regular analog, cable TV program (which I believe here in North America will be 4:3 NTSC inlerlaced) in FULL mode on my Pioneer widescreen TV, it is definitely horizontally stretched (or vertically squished, I guess). Absolutely no question in my mind; the picture is distorted. So, to say there is no stretching going on would seem to be incorrect. Beyond that, I can not seem to make all the evidence match.

Anyway, if what you say is 100% technically correct, then it is disppointing that so many other self-proclaimed experts on the internet are wrong. I guess the lesson learned is never believe what you read on the internet. Myself, I guess I'm just frustrated trying to understand the whole thing. Thanks for your input, Don.

 

[Patrick Sun]

I think the confusion is between "Full" mode for 16x9 TVs and "FullScreen" mode when talking about DVDs.

If you ever saw a 4:3 HDTV set (I own one), you know that the ATSC reception of HDTV 1080i material can be displayed in the 4:3 mode (but this makes people look tall and skinny, and to get the correct aspect ratio, you have to make your 4:3 HDTV set go into 16x9 mode. This is the default "Full" mode on more typical 16x9 HDTV sets, but not on 4:3 HDTV sets. As mentioned earlier, some 16x9 TVs will lock into "Full" mode when a progressive video signal is detected, and that is not always the desired result (like when a non-16x9 enhanced DVD is being played, which then really squeezes down the vertical resolution so that people look short and fat ).

16x9-enhanced DVDs of films with aspect ratios of 1.78 and greater benefit from TVs that can display such an image by squeezing (vertically) the image into a 16x9 aspect ratio on the TV screen. The video image on DVDs is still authored to be within a FULL 4:3 frame, but with 16x9 enhancement, more of the video frame is used for video, and the video image then relies on the vertical squeeze of the TV set to display it properly with an increase in resolution (by utilizing as much vertical resolution available in the 4:3 frame to be displayed properly when vertically squeezed later by the TV), otherwise downconversion is performed by the DVD player when the video is sent to a TV set that can't vertically squeeze the video image properly to arrive at the proper aspect ratio, but with less vertical video resolution.

Now, for 16x9 HDTV sets, to avoid screenburn of watching 4:3 video material (where you have sidebars when the proper aspect ratio is displayed), some TVs have the "Stretch" mode to pull the 4:3 material horizontally to fill the entire 16x9 aspect ratio screen.

 

[Phil Nichols]

That doggone word "squeezing" is a main source of confusion.

What it really means (or at least orginally came from ..... when most TV's used CRT-based technology) is the reshaping of a 4X3 screen's scan lines so they no longer go all the way to the top and bottom of a 4X3 display's visual field. Hence the term "sqeezing" - whereby the beam control circuits shortened the vertical beam scan height and re-centered the scan field so that the scan field became a 16X9 geometric shape on a 4X3 CRT-based display - still all the way out to the sides, but "in" some from the top and bottom so as to make a 16X9 shape.

Within this 16X9 geometric shape is where 1.85:1 and 2.35:1 anamorphic images then appear on the 4X3 display when it's in it's "squeeze mode". I suspect that 2.35:1 anamorphic's, when shown on 4X3 displays in squeeze mode, actually have the usual small top/bottom bars WITHIN this new 16X9 squeeze-generated shape! (....not counting the main big top/bottom bars made when the base 16X9 shape is created on a 4X3 display's visual field).

So ............ squeezing merely forces a 4X3 display's mormal base display area to be 16X9 instead of 4X3 by not having active a portion of the top and bottom of the 4X3 shape but still having all scanning lines available because they are now condensed vertically into the 16X9 height. A properly designed 4X3 display device in squeeze mode should place DVD images into this newly created 16X9 region the same way(s) as a native 16X9 display device places them.

George, your original "The mode called "Full" would stretch the frame horizontally to fill the 16:9 screen." statement about Pio Elites is not complete. "Full" means the scan field raster on the screen is sized perfectly to just go (ignoring over-scan) all the way out to the sides and all the way to the top and bottom of the 16X9 shape. Therefore, HD content should perfectly fill the Elite 16X9 screen WITHOUT distortion when in "Full" (..which Pio Elite's automatically go into when their circuits sense non-480i frequencies coming in). The only distortion you get on a Pio Elite when it's in "Full" mode is width-stretching you get when trying to feed it material of 480i frequency, which by definition is NOT "HD". In "Full" mode, 4X3 material and letterboxed 480i material (..which is designed to fit "inside" a 4X3 shape in the US), you indeed do get distortion-stretching out to the sides of your 16X9 shaped Pio Elite visual field.

BTW, IMHO, "Natural Wide" makes perfect sense as a descriptive term. As this Pio exclusive is designed to leave 4X3 material as natural looking as possible while still reshaping it wider to 16X9.

 

[Don Munsil]

I'll leave aside Phil's comment about "natural wide" as he knows my feelings about that.

Folks, this is very simple. In NTSC and PAL, you can have 4x3 video or 16x9 video. Those are (so far) the only two aspect ratios available. Sadly, there is no way to distinguish the two electronically. The signal looks identical to your TV. So the TV relies on you, the viewer, to tell it what the aspect ratio of the video is. So if you take 4x3 video and watch it in FULL mode, it most definitely looks stretched. The TV doesn't have to do anything special to make this happen - it just takes you at your word and displays the video as though it was 16x9.

Conversely, if you take 16x9 video and watch it in the set's 4x3 mode, it will look squished horizontally. Again, this is just a mismatch between the aspect ratio of the video and the display mode on the TV. It tells you nothing about what the "real" aspect ratio of the video is. The only thing that will tell you that is viewing it or looking at the notes on the back of the DVD case. Or some DVD players automatically adjust the aspect ratio on the fly, which will tell you what the "true" aspect ratio of the video is as well.

Is 16x9 video "stretched"? No, any more than 4x3 video is "squished." Both are valid video formats, and neither is the "correct" kind of video.

Keep in mind that this is all pretty conceptual; physically what is happening is that on a 16x9 set, the raster is being left alone in FULL mode, and extra processing is added for 4x3 mode to add black bars on the sides. On a 4x3 TV, 4x3 signals are left alone, but the monitor goes into a special "raster squeeze" mode to view 16x9. So one TV "squeezes" 16x9 video to make it fit a 4x3 display, and one "squeezes" 4x3 video to make it fit a 16x9 display.

Ultimately, the important thing to know is that the video on a 16x9 DVD is plain, ordinary 16x9 video. It's not "squeezed" 4x3 video. 16x9 video can be recorded on a VHS tape, for example. And if you watched it on a 4x3 TV with no 16x9 mode, it would look squished. That doesn't make it "really" 4x3 video. The fact that you can watch 4x3 video in 16x9 mode or vice versa doesn't change the fundamental aspect ratio of the video.

It would have been much better for all concerned if when 16x9 video was developed, a special flag was encoded into the video stream that would tell the display what the aspect ratio of the video was. But they didn't do that, and we are left with the current situation, which is clearly confusing to lots of people.

As to my credibility, George, I really am going to leave it to you to check me out. Start with Google. I tend to think you'll find I'm a pretty credible source for video information. Yes, there are lots and lots of people who mentally think of 16x9 video as "squeezed" into a 4x3 space, but they're wrong. It's an OK mental model at first, but it leads directly to the conundrum that led to your original post, and then to rationalizations like "FULL is different for HD" which is completely false.

Best,
Don

 

[Brian L]

"FULL is different for HD" which is completely false.

I may have been partially responsible for interjecting some of that into the discussion.

George commented on an issue with a Pioneer TV. FWIW, the Pioneer's I am familiar with have separate user settings called "Full" (which is used for enhanced DVD) and "Full for HD", which it locks into when getting a 1080i signal.

When you converge the set, you must select each mode separately.

Now, all that may be completely irrelevant to the discussion, but it does lead one to make an assumption that there is a difference in processing, at least in terms of the set in question.

BGL

 

[Matt DeVillier]

It would have been much better for all concerned if when 16x9 video was developed, a special flag was encoded into the video stream that would tell the display what the aspect ratio of the video was. But they didn't do that, and we are left with the current situation, which is clearly confusing to lots of people.

Don,

if this is true, then how do some of the 4x3 480i Sony Wega sets auto-detect a 16x9 signal from a dvd player and perform the vertical squeeze automatically?

 

[Phil Nichols]

Matt,

If your question is correct, Don will have to answer it.

But are you sure the Wega's are auto-detecting a 480i 16X9 signal from the DVD player or - a progressive 16X9 signal from the DVD player? It seems to me sets would auto-detect 16X9 anamorphic material based on field frequency - hence they are auto-vertical-squeezing on 480p ........ not 480i.

 

[Matt DeVillier]

Phil,

no, this was a feature of the non-XBR wegas starting around 1999 or so, and were definitely 480i only. The base FS model (which I had) had a 16x9 mode that you needed to activate from the menu, but the higher up FV model auto detected a 16x9 signal and compressed the raster area vertically.

 

[Don Munsil]

Sony implemented WSS (Wide Screen Signalling) on some of their 4x3 NTSC TVs and some of their DVD players. Kudos to Sony for taking a stab at this problem, but I believe it's only a PAL standard, and Sony just appropriated it for their NTSC sets. It's possible that it's a legal (but obscure) NTSC standard, and only Sony implemented it, but I can't find any reference to it in the specs.

On the other hand, 16x9 NTSC video isn't obscure at all. It's a recognized standard, and the docs for it don't mention WSS at all, as near as I can tell. I don't have all the specs available, so if someone knows different, I'd love to know the straight dope.

They've had widescreen (16x9) TV for much longer in Europe, so perhaps they've just had longer to work out all these problems. But we've had widescreen for years, and other than the Sony TVs that Matt mentioned I don't know of a single TV that implements WSS sensing, at least in this country. I hear that it's a commonly used feature in Europe, but again I don't know personally.

What I'm trying to get across is that when 16x9 video was defined, they should have seen this coming and defined a clear unambiguous 16x9 signalling standard for NTSC and propagated it everywhere, most especially to DVD, which was the first mass-market 16x9 video source available.

Maybe there is a spec, but if so no one seems to know about it. One way or another, the CE industry has dropped the ball on this.

Don