Would a 120 or 240hz HDTV Produce a Better Picture?

Kevin's not satisfied with his 60hz HDTV's image quality. He asked if a 120 or 240hz HDTV would improve the picture.

It's hard to say whether a faster refresh rate really improves the quality of an LCD-based HDTV. In some cases, it can actually hurt.

While reviewing HDTVs for PC World, I've noticed that 120 and 240hz LCD sets generally outperformed 60hz sets (I put that in the past tense because I haven't reviewed a 60hz HDTV in a very long time). But there were always exceptions, and it's difficult to say to what degree the refresh rate was the cause. After all, the higher refresh rates came on the newer models that also sported other improvements.

I should note, however, that I never saw any evidence that 240hz sets generally look better than 120hz ones. The advantages of a fast refresh rate, at least with 2D HDTVs, seemed to top out at 120hz.

The faster refresh rates have one undeniable advantage, although it's one you're not likely to see very often. They fix one problem that turns up occasionally when viewing film-originated content off a Blu-ray disc.

Films are shot and meant to be projected at 24 frames per second (fps). But American television and home video usually runs at 60fps. Therefore, converting a movie to video requires turning every 24 frames into 60 frames. Since 60 doesn't evenly divide into 24, there's inevitable distortion. Fortunately, this distortion is minor and rarely a problem. (I'm simplifying things considerably here.)

The Blu-ray format offers a fix for this problem. The discs can be, and most are, mastered to play back at 24fps. But on a 60hz set, the video still has to be converted. On the other hand, since both 120 and 240 divide evenly into 24 and into 60, each standard frame rate can be displayed without distortion.

But HDTV manufacturers like to brag about another "advantage" of these high refresh rates, one that may do more harm than good. Every high-rate HDTV I've ever seen has the ability to extrapolate virtual frames in between the real ones, in theory producing smoother motion. The manufacturers like to advertise this trick with brand names like Motionflow and True240hz.

As a general rule (and this varies from one manufacturer and model to another), this seems to help only with lateral, already-smooth motion, like the crawling text under news and sports shows. With anything more complicated, these virtual frames can often make things worse.

Fortunately, all HDTVs allow you to turn this feature off, and many will let you turn it down a notch, as well. I recommend you look at a favorite action scene or sporting event, trying different settings, and pick the one that looks best.

Contributing Editor Lincoln Spector writes about technology and cinema. Email your tech questions to him at answer@pcworld.com, or post them to a community of helpful folks on the PCW Answer Line forum.

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