The HD Channels Mystery
You’re finally able to fully enjoy HD channels because you purchased that 60-inch plasma TV you’ve wanted for a couple of years. You get it home, mount it properly and hook it up. You turn it on and “HEY! What’s this!?! There are black boxes on the TV!” The picture doesn’t fill the whole screen. You’re confused. You’re upset. I know. I was, too. At least until I began understanding the technology behind why about a third of my screen was blank.
Letterbox Format on HD Channels
When you see video on those HD channels where there are black areas above and below the video image (these are mattes), you’re watching video that was shot in a widescreen aspect ratio and then transferred to a standard-width (TV) video format. All of the original video image data is preserved when this transfer occurs. The original aspect ratio is also preserved. The term letterbox came about because it looks like an old fashioned letter slot; in other words rectangular versus a square, like we’re used to with TV. It’s also called the widescreen format.
Compare It to a Movie Theater
If you’re good at math, next time you go to a theater to watch a movie, do some quick mental calculations. What you’ll see is that the new movie format is close to a 2.35:1 ratio, or 2.35 units of width for every one unit of height. Your big-screen plasma TV, if you measure it, has a ratio somewhere closer to 16:9, or 4:3, or, 1.33:1.
What these differences in aspect ratios mean is that when the movie is formatted for viewing on a television, it’s going to appear stretched horizontally to fit properly. Thus, the mattes are purposely placed in as part of the video image to make up the difference. Many times these mattes are used to place enhanced data, such as subtitles without having to overlay the video image, detracting from your enjoyment of the movie. I’m old enough to remember the days of the Beta and VHS video tape where the subtitles were placed directly over the video image, usually at the bottom. It was very distracting.
Video Aspect Ratios
Today’s high-definition, widescreen TVs are usually designed to be large rectangles instead of squares. However, not everyone is lucky enough to have one of them — yet. So, most non-HDTV video is broadcast to fit the smaller, square-ish TV screens still in use. So, when you watch HD channels on a regular TV, you’re going to see mattes.
Where we run into problems is when we get to HDTV video formats. Most of them are shot in widescreen aspect ratios (usually 2.35:1), instead of the square-ish format that most of us have been used to for years. When the video is shot in an HDTV format (usually Panavision) they normally just cut part of the width off and broadcast it, causing you to lose part of what the director wanted you to see. So how do they make all of the widescreen image fit on your square TV? They have three options, but normally only use two.
The first option is by using compression. This where they shrink the width of the video image so that it fits into the square of your TV. However, when this happens, you get a pretty distorted video image, that’s not all that enjoyable to watch. You get a Roseanne Barr that looks almost like Paris Hilton — tall and skinny, instead of short, and, uh, not skinny.
The second option is to “letterbox” the video. This is where they shrink BOTH the width AND the height equally. However, when this happens, the height of the video image doesn’t completely fill the screen, while the width usually does. This maintains the correct dimensions of the video image, so Roseanne looks like Roseanne. And you don’t end up laughing through a drama because everybody looks funny.
The third option is called “pan and scan.” This is where the editor just chops the edges of the original film so it fits the square box of your older TV. You can tell when this has been done because they’ll tell you, “This video/movie has been modified from its original version. It has been formatted to fit your screen.” But doing this kinda messes things up for the credits, because it usually tends to chop off parts of names and titles. So they’ll revert it to the original format for the intro and exit titles.
That’s right. I said blame Hollywood. This is because back in the early days of the silver screen, Hollywood directors and filmographers got together and decided on the screen dimensions. They wanted a wider format video image to “wrap around and engulf the viewer in the video imagery of the movie and provide an awe-inspiring movie experience.” Remember, TV was almost unheard of back then, so they had no idea what they were doing to us home viewers several decades later.
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