indessed roscivs

From SDTV to HDTV, from 480p to 1080i, millions are asking—what does it all mean? Here’s my attempt at a simple guide to help people through the confusing mish-mash of numbers and letters.

There are four basic parts to understanding different television formats: aspect ratio, resolution, frames-per-second, and interlacing. Let’s take a look at each of these different areas in turn.

Aspect Ratio

Different video formats have different aspect ratios—or, in other words, they differ in how wide the picture is compared to how tall it is. A perfect square has an aspect ratio of 1:1—the square is exactly as wide as it is tall. A rectangle that is exactly twice as wide as it is tall has an aspect ratio of 2:1.

Note that there’s nothing inherent to an aspect ratio that determines how good a picture looks—it just determines how square or rectangular a picture is. For example, you might have a 6″x4.5″ photo and a 40″x30″ poster—both have exactly the same aspect ratio (1.33:1, or more commonly 4:3), but obviously there are other important differences.

The time when it does make an important difference is when you’re viewing content that was originally a different aspect ratio. You can imagine taking your 6″x4.5″ photograph and putting it in a picture frame:

If your picture frame is also 4″x6.5″, then you have no problem. But if your picture frame was designed for a much wider 4″x8″ photograph (2:1), then you’ll have a little bit of empty space on either side of your picture. On the other hand, if your picture frame was designed for a square 6.5″x6.5″ photograph (1:1), then you’ll have a little bit of empty space on the top and bottom of your picture. Either way isn’t going to look very nice.

We have the same problem with different video formats. Movies are often shot in 2.35:1 or 1.85:1, a very rectangular or “wide screen” format. Standard television for the past few decades has been 1.33:1, which is nearly square-like. So when watching movies on television, you’d have empty space on the top and bottom of your picture (the infamous “black bars” or “letterboxing”), just like a photograph in a frame that doesn’t quite fit.

All different types of HDTV are standardized on 1.77:1 (or more commonly “16:9″), which is right in the middle. That means that watching movies on a 16:9 screen will result in a slight gap above and below the picture, but not much. And watching standard television on a 16:9 screen will result in a gap to the left and the right of the picture.

There are also other methods of getting mismatched aspect ratios to fit for people who dislike that empty space. These methods are usually considered bad, because they either distort the picture in some way or they crop out some of the picture. For example, “Stretch” mode, which is the default on many 16:9 TVs, will make people look short and fat if the original is 1.33:1, or tall and skinny if the original is 2.35:1. “Pan & Scan”, which cuts off the sides of 2.35:1, used to be popular in VHS releases of movies. And many widescreen TVs have a “Zoom” feature, which cuts off the top and bottom of 1.33:1.

I’d recommend just sticking with the black bars. That way you’re seeing 100% of the undistorted original.

Tomorrow, I’ll talk about resolution, and the role that plays in different video formats.

This entry was posted on Wednesday, May 16th, 2007 at 3:41 pm and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.