Understanding HDTV Aspect Ratio

March 2nd, 2011 · 7 Comments · 21:9 3D LED LCD Flat Panels, Blu-ray Discs, Front Projection, LCD Flat Panel, LED LCD Flat Panels, Microdisplay Rear Projection, Plasma

Given the recent announcements of ultra-widescreen LCDs and projectors, we thought it time to revisit one of the more confusing aspects (pun intended) of TVs and movies: aspect ratio.

No matter what, every TV is going to have black bars on some content, and the reasons why are complex. Let’s take a look at the what and the why of HDTV aspect ratios.

In the olden days of the 90′s and before, all TVs were 4×3. This means that for every four inches of screen width, it was three inches tall. If you prefer decimals, this is also called 1.33:1. Here’s a 4×3 image of some tower I saw on a vacation a few years ago.

Paris by Geoff Morrison 4x3

Movies have long been wider than that, initially to give something different to audiences than that upstart television (more on this later). So when HDTV came out, it was decided to give the consumer a wider display, to be more like those neeto movies. Many films are 1.85:1, all TV programming at the time was 1.33:1, so some genius decided that instead of having some programming that didn’t have black bars, an entirely new aspect ratio was created: 1.78:1, or 16×9 (math majors will note that it’s really 1.777777:1, but let’s not muddle the point). Here’s the same shot, but 16×9:

Paris by Geoff Morrison 16x9

Notice there’s more on the sides. Overall it looks a little cooler, right? A little more cinematic? The problem is, we’ve had 60 years of 4×3 content. So anything 4×3 you want to watch ends up looking like this:

Paris by Geoff Morrison 4x3 on 16x9

Now I’ve never understood why people get apoplectic about black bars, but there you go. Some get fixated on the black bars instead of just watching the TV. Unfortunately for them, it gets worse.

As I mentioned above, many movies are 1.85:1. If you’re watching one of these films, and you’re not overscanning (and presuming the film is being presented in its original aspect ratio), it’s going to look like this:

Paris by Geoff Morrison 1.85 on 16x9

Not that big of a deal, right? Barely noticeable bars. We’ve had movies even longer than TV, and there has never been a “standard” aspect ratio. The common ones are 1.85:1, 2.35:1 and 2:40:1, though a few films were even wider, 2.55:1 or even 2.76:1. Most big Hollywood movies are 2.35:1 (usually pre-1970) or 2.40:1 (after 1970) though there are exceptions. Here’s what a 2:40:1 movie would look like on a 16×9 screen:

Paris by Geoff Morrison 2.40:1 on 16x9

These aspect ratios are often referred to as “Cinemascope” though this isn’t really accurate (just like not all copy machines are Xerox, not all hook-and-loop is Velcro, and not all tissue is Kleenex).

Anamorphic Lenses

Over the past few years, anamorphic lenses have become popular in home theaters. These, in conjunction with a projector that supports it, allow for a 2.40:1 image to be shown on a 2.40:1 screen using only a 16×9 aspect ratio projector. The projector stretches the image vertically to fill the 16×9 chip, which looks like this:

Paris by Geoff Morrison 2.4 anamorphic on 16x9

Then the lens stretches it out to fill the screen:

Paris by Geoff Morrison 2.40:1

This is very cool from a presentation standpoint. There are also some other benefits. If the scaling is done correctly, you could gain a slight increase in perceived resolution in the same way that scaling a DVD does. After all, a 2.40:1 movie on a Blu-ray is only using 800 lines of vertical resolution, the other 280 lines are just wasted on the black bars. So scaling this up to fill the DLP, LCD, or LCOS chip (or chips) isn’t necessarily a bad thing. Done poorly, though, and you could introduce artifacts. Using the entire chip (or chips) could also boost the light output somewhat, as the entire chip is being used to create the image, instead of just a portion.

There are some negatives, though. In addition to the potential for scaling artifacts, the lens itself can be a problem. Cheap lenses will reduce light output, potentially offsetting or at least diminishing the gain caused by using the whole chip/chips. They could reduce resolution as well. Even with excellent lenses, diffraction is issue. The light is exiting the glass or plastic projector’s lens, then entering a whole new lens, then exiting that lens. These extra layers of diffraction are almost certainly going to reduce contrast ratio. Some of the light is going to be reflected back into the projector’s lens, adding further light pollution to the engine, decreasing contrast ratio further. Is it going to diminish performance enough for you to care? Maybe, maybe not, but it’s worth noting that adding lenses isn’t without a cost.

Constant Height/adjustable width/masking

The next level in the anti-black-bar camp is constant height, where the screen is able to adjust its aspect ratio to match the video. This is usually done with curtains or some other material on the sides that hide the unused portions of the screen from view. This masking tricks the eye into thinking the screen is exactly the same aspect as the material. Unless you want to do it yourself, it’s pretty expensive as it requires a lot of mechanicals to move the masking around.

Native Wider-Screen

Recently, Vizio, projectiondesign, and others have released displays with a wider-than-wide native aspect ratio. The projectiondesign projectors are 2.35:1 natively, with a resolution of 2538 x 1080. The Vizio models have a resolution of 2560 x 1080, or 2.37:1/21×9. While it’s mildly frustrating that this isn’t exactly 2.35 or 2.40:1, it is at least right in the middle, allowing for only slight back bars on either. Here’s what a 2.40:1 movie looks like on a 2.37:1 screen, notice the tiny, tiny bars on top and bottom:

Paris by Geoff Morrison 2.40: on 2.37:1

This is also basically what a 2.40:1 movie will look like on the projectiondesign’s 2.35:1 screen. At the resolutions of these images, you wouldn’t really be able to see the difference.

Here’s a 2.35:1 image on a 2.37:1 screen, notice the tiny bars on the sides.

Paris by Geoff Morrison 2.35:1 on 2.37:1

Honestly, if black bars this size bother you, I would have to recommend alternate assistance.

But, and there’s always a but. When you watch 16×9 material on one of these displays, it looks like this:

Paris by Geoff Morrison 16x9 on 2.37:1

And 4×3 looks like this:

Paris by Geoff Morrison 4x3 on 2.37:1

Admittedly, that’s a bit more substantial.

“Zooming In”

While it may seem obvious to just use the TV (whatever it’s native aspect) to “zoom in” on the image to eliminate the black bars, there are several reasons why this is a bad idea. The first is that you’re losing resolution. No matter how good the scaler is in the TV, zooming in on the image will result in a softer image. If the scaler in the TV isn’t good, there could be significant artifacts introduced that aren’t there in a “per-pixel” or “native” mode. These could range from jaggies to moiré patterns that are far worse than just “black bars.”

Also, and this is the argument that most often falls on deaf ears, the aspect ratio of the movie is what the director intended. They designed a shot with a specific idea in mind. Cropping the sides loses information. If you don’t care about this, well that’s your decision, but personally I don’t understand it. You’re trusting this director to entertain you for 2 hours, but not enough to assume he knows more than you what a shot is supposed to look like? *Shrug*

Conclusion

No matter what, you’re going to have black bars. If you’re the type of person who can’t handle this, well, constant height projection is really the only option. I can’t advocate zooming in on the image for the reasons listed above. Not only does it diminish the image, but it ruins the director’s intent.

I’ll end with this: I’ve had a 2.40:1 screen as my main “TV” for over a year. The VAST majority of what I watch on it is 16×9. In the dark, no one notices the “bars” on either side. For those big movies, though, having an uber-wide 10-foot screen is way cool.

 

—Geoff Morrison

 

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7 Comments so far ↓

  • Jan Andersen

    Thanks for this article.

    A tiny comment as to displaying 2:40 or 2:35 content on a 21:9 TV – this isnt really a problem on a proper 21:9 TV set, the picture is fit to the 21:9 screen automatically, and it cant be seen by the eye that a fit has been done.

    You hardly can see when 16:9 content has been fit to a 21:9 screen, using a combination of streach and zoom – but depends on the aspect ratio of the source – 1:85 content usually looks better.

    Having a proper TV ( a 21:9 ) you do notice that many films in 1:85 displayed on a 16:9 TV have horizontally been compressed to fit 1:78, by people look a tad skinny on a 16:9 TV.

    Having a 21:9 you would zoom and streach the 1:85 format, and actually most of the times get a more accurate picture in terms of all people not being on a diet – or you could say, either compress a little or streach a little.

  • Geneurônios

    Sorry, made a mistake … Jeff Beck is 1.78:1 , but looks different!!
    Can you explain me the difference between the Blu-rays I have mentioned?

  • Geneurônios

    HD Guru, I have an Infocus IN81 and project in 120″.
    1 – I have the Blu-ray “Jeff Beck at Ronni Scotts” and it is a perfect 1.85:1.
    2 – I have the Blu-ray “Joe Satriani in Montreal” and it is 1.77:1. Despite the excellent PQ, the aspect ratio looks more like a 1.33:1. Why the producers did this???
    It is very bad!!!

  • Jerome

    I clicked on narrative “How to Set Aspect Ratio etc” and get a disseration on “Understanding Aspect Ratio etc”. Not a word on How to set it!!!

  • John Bishop

    Geoff,
    Good topic that touched on a few interesting points. The aspect ratio of 16×9 is halfway between 1.33:1 and 2.35:1 which were the extreme most aspect ratios considered when SMPTE was determining what AR to recommend for HD. 1.33, 1.66, 1.85, 2.20, & 2.35 were all considered important for the new TV format to handle. Turned out that if all were layered atop each other in equal area form, they would be encompased by a 1.77:1 rectangle on the outside, and would cover a 1.77:1 rectangle on the inside. Good a reason as any I guess:)
    In cinema, widescreen came as resolution was improved, all with the goal of increasing the field of vision for the viewers. More immersive ment more impact for the art. Lowell Thomas said in an interview after the screening of This is Cinerama, the king of immersive formats, that even General Jim Doolittle, the WWII ace, clutched the arms of his theater seat when the aerial scenes dropped over the edge of the Grand Canyon. The greatest benefit of the anamorphic projection process is it upconverts the 800p on the disc to a 1080p image. Perceived resolution goes up because 33% more pixels are delivering the color and contrast information. Light levels increase by 1/3 while pixel dimension decreases by 1/3, improving edge detail and making them more invisible at the target viewing distances. The small trade-off of good processing to scale the image is well worth it, when the optics that do the widescreen expansion are also of the highest quality. A very few percent loss from the scaling and lens is traded for a 33% gain in the parameters mentioned. When done well, home theaters can be designed to a cinema standard for viewing geometry. That doesn’t necessarily mean a 146 degree field of view like Cinerama, a 3x35mm system, but it certainly does mean we can go well beyond TV standards with today’s sources. Think about it, back in the CRT days we rarely used screens under 100″ diagonal for a serious theater. That’s 60×80″ for the 4×3 screens typical of the day, and those of us designing Runco systems had the ARC-IV which allowed us to build 1.85:1 systems at 60×111″. Today, my circle of associates (Society of Personal Cinema Architects) call a 10′ wide screen small. That’s because its only about 4′ high. At 5, 6, & 7′ you begin to get cinematic scale in typical spaces, and that’s the experience we want to mirror from the best Hollywood has to offer. Row 9 at the Samuel Goldwyn Academy Theater is less than 2 screen heights away from the image, and is considered by many to be where the prime seat range begins. Setting that experience as the goal creates a series of decision points that lead to a best case home cinema experience and the anamorphic process you touched on is a key enabler of achieving that goal.
    Incedentally the non-anamorphic process a native 2.35 chip would enable is certainly a hope, but the 2560 models coming out may not be the answer. These are in fact re-issue commercial 16×10 chips of 2560×1600 pixels. There will be some dramatic non-linear scaling required for 2.35 and HD as well. They are the smaller TI chip and will have those image limitations as well. The geometry should be good, but I’m skeptical that the image quality and flat field uniformity will compete with the better scope technologies we’re using today. At some point TI might create the scope format chip for digital cinema, and then maybe we’ll get that and content that is 1080p anamorphic scope….now we’re really talking! Thanks for the nice article, I’ll stay tuned for more on the widescreen flat panels, they could be fun.
    Our motto is; wider and brighter is better.
    Best Regards,
    John Bishop – Personal Cinema Architect

  • Bryan

    Geoff, What 2.40:1 screen do you have as your main? Also how does the image quality compare to the kuro elites and the panasonic VT25/VT30? Also is there a upcoming ultra-widescreen TV that looks to be of good quality imagewise?

    Geoff: I use a projector and a 1.0 gain screen. The projector depends on what I’m reviewing. Right now I have a JVC DLA-X7 which sadly has to go back soon. Easily better than any plasma or LCD. Also, bigger.

    From what I’ve heard the new Panasonic plasmas will have near-KURO black levels. I’m sure Gary will be testing one and we’ll see.

    As far as the native widescreen displays go, they’ll likely perform about the same as their respective technologies. Adding pixels and width doesn’t fundamentally change the performance of a display in itself. The easiest way to think about it is that all TVs are cut out of a sheet of cookie dough (or motherglass or wafer). Ultra-widescreen sets just have a more rectangular cookie cutter.

  • cbono

    Is there a tolerable amount of cropping consumers/viewers should ever have to accept? Is there a tolerable amount of geometric distortion consumers/viewers should ever have to accept ? In particular, can you even begin to explain why some cable/satellite channels/providers persist in displaying some programming and commercials in improper aspect ratios? For example “Bones” reruns on TNT HD as viewed on Dish Network.

    Geoff: Sadly, a question for the ages. TNT has been the worst offender of stretched and upconverted SD since their inception. My only guess is that it’s cheaper to get the SD feeds and upconvert them.

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