120Hz HDTVs: The Secret to Making Movies Look as Smooth as Butter



Click to viewWhile the rest of the world is gawking at 108-inch LCDs and quad-resolution pixel counts, I'll let you in on a little secret: 120Hz HDTVs are going to help movies look better than ever on the little screen in your living room.

Here's how.

Film is 24 frames per second. That standard was the approximation of what was defined in the early 20th century by hand crank cameras. And just about every movie disc you can buy is encoded in this format. We're not just talking DVD. We're talking about HD DVD and Blu-ray, too.

The problem is, most TVs run at 30 frames per second. Fitting that 24-frame content onto a 30-frame screen isn't that easy; the math just doesn't compute cleanly. You can't divide 24 by 30 without filling in the gaps with some junk. That junk causes stuttering in the video. This is a jerky-looking phenomenon that's particularly noticeable when the camera pans across a scene. The conversion is better known by film and TV wonks as 2:3 pulldown. It spreads out 24 frames into 30 by placing one frame on the screen three times and the next one after that two times, and repeating this pattern ad infinitum.

How does this relate to an 120Hz HDTV showing frames at 120 frames per second? A bit of simple math tells you that 120 is a multiple of 24, because 24 x 5 = 120. So one of the claims of the purveyors of these sped-up monitors is that they can natively reproduce 24p programming, namely, just about every film has ever been shot.

These new HDTVs avoid this awkward 3:2 pulldown process altogether by changing their frame rate to something that's a multiple of 24 by using either frame doubling or interpolation (also called "tweening"). Then, their playback can be as close to native 24fps playback as you can get. That's why 72Hz (24 x 3 = 72) and 120Hz refresh rates are gaining traction. Native 24p playback: Yeah, sounds good. But how will it be implemented and which manufacturers are involved? And who does it best?

Next in our series: Which TVs and disc players are in on this nascent 72Hz/120Hz phenomenon, and which method of frame expansion does each use? Is this going to cost a lot? How much better will it look? Here's part 2.