Every year it seems there's a new catchy spec in the HDTV realm everybody likes to talk about. A few years back it was 1080p resolution. Then we heard about 120Hz, which is supposed to reduce motion blur in fast-moving images on LCD TVs. Well, this year, the latest and greatest spec is 240Hz, which is supposed to do what 120Hz does, but better.
Not too long ago, our video guru David Katzmaier gave his initial impressions on 240Hz in a post titled "Is 240Hz worth waiting for?" When he wrote that piece, he'd just seen his first 240Hz TV in action and wasn't sold on the new technology. Now that he's reviewed four 240Hz HDTVs and has a fifth review (the LG 47LH55) in the works, he's still not sold, but he admits the verdict isn't totally clear-cut.
Part of the problem is that there's a difference between what your eye sees in everyday material you watch and objective testing done with test patterns. As Katzmaier notes in his post, "Standard LCD and plasma TVs refresh the screen 60 times per second, or 60Hz, which is plenty fast enough to eliminate flicker and create the illusion of motion from a series of still images. In fact, most sources sent to your display arrive at the nominal rate of 30 frames per second, and each frame is repeated once by the television to achieve 60 total fps."
For most people, including me and Mr. Katzmaier, it's very difficult to see the impact that "faster" LCD sets have on picture quality. We spent some time in our AV lab watching various source material from 120Hz TVs and 240Hz models and it's really hard to detect any difference (it's hard to detect any difference between 120Hz and 60Hz models, too). To be clear, I'm referring here to motion-blur reduction because of faster refresh rates, not to dejudder processing, which smooths out motion and makes film-based material shot at 24fps look more video-like. When dejudder is engaged, you can easily spot its impact on the picture. (It's also worth mentioning that the dejudder processing on the 240Hz TVs we tested so far wasn't any better--or worse--than than the dejudder on 120Hz TVs).
All that said, when it comes to motion blur, not every set of eyes and every brain is created equally and, as Katzmaier points out, "Some viewers can perceive motion blur in fast-moving objects on standard 60Hz [LCD] models (motion blur like this isn't an issue with plasma or other display types, whether 60Hz or otherwise, because they use different methods to create the illusion of motion)."
To reduce blurring, most 120Hz LCD displays use a system called MEMC (motion estimation and motion compensation) to slip in a new frame between each of the original frames. The end result is one extra frame for every true frame.
You'd think, then, that a 240Hz TV would just double up to achieve an even more blur-free picture. Alas, it's a little more complicated than that. The problem is there are actually two different types of 240Hz, including one that doesn't bill itself as true 240Hz but rather as a "240 effect." Here's a breakdown of the two versions and which companies employ them.
- MEMC (motion estimation-motion compensation): Both Sony and Samsung 240Hz sets use MEMC to basically double the 120Hz process described above. However, instead of getting one extra frame for each "true" frame, you actually get three extra frames. (See reviews of the Sony KDL-52XBR7, the Sony KDL-XBR9 series and the Samsung LNB750 series).
- Scanning backlight (240 effect): LG, Toshiba, and Vizio use what's called "scanning backlight" technology. Such TVs use MEMC once to get to 120Hz, but instead of doubling the interpolation, a backlight flashes on and off very quickly to achieve what Toshiba calls a "240Hz effect." LG, for its part, fails to make that distinction and uses the 240Hz term without qualification to describe its scanning-backlight models
After having reviewed three 240Hz TVs that use MEMC and one, the Toshiba 47ZV650U, using the scanning backlight, Katzmaier reports that the MEMC version of 240Hz is slightly superior at reducing blur. But when he says that, he's referring to test patterns where models from Sony and Samsung scored slightly better than the Toshiba. MEMC displays delivered between 900 and 1,000 lines of motion resolution, which matches the result of a typical plasma, while the Toshiba scored between 800 and 900. But again, watching everyday material, whether it be from a Blu-ray movie or HDTV content from your cable or satellite provider, he and I both maintain that the difference between having a 120Hz LCD TV and a 240Hz TV is virtually imperceptible. In other words, superiority is a very relative term in this instance.
In terms of what kind of premium you'll pay for a 240Hz TV over a 120Hz model, you're currently looking at somewhere between $200 and $400, and we expect that by next year the gap will be even smaller. So, is it worth the premium?
At this point, the answer is probably no. Objectively, in lab tests, you can't dispute the fact that 240Hz does seem to reduce motion blur. But in real-world terms it doesn't amount to much, if anything. But as I always say, if you want the latest and greatest spec--and don't mind paying a little extra--go for it.
Feel free to comment.
David Carnoy
[reviews.cnet.com]
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