Understanding HDTV Aspect Ratio
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.
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:
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:
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:
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:
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).
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:
Then the lens stretches it out to fill the screen:
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.
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:
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.
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:
And 4×3 looks like this:
Admittedly, that’s a bit more substantial.
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 moirÃƒÂ© 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*
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.
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