Higher Refresh Rates In LCD TVs: Do They Make A Difference?

Posted by: David Birch-Jones at 5:05 pm, August 12th, 2009

These days, most, if not all, of the latest LCD flat panel models in the middle and upper pricing tiers feature either 120 Hz (double) or 240 Hz (quadruple) screen refresh rates (480 Hz models are on the horizon). The marketing materials typically tout “greatly improved sharpness with fast-motion images,” but in the past I’ve opined more than once that with actual program material, the visible improvement isn’t all that much. It doesn’t help that many sets include a split-screen demo mode that usually feature a slowly panning high-resolution still image, which—naturally—does show a significant improvement on the processed side, but without showing how higher refresh rates will affect real-world program material. (In fairness, there are at least a few sets out there that feature split-screen demo modes that let you see the effects of higher refresh rates with actual program material—although they’re in the minority.).

With actual program material however, I’ve found there’s often little discernable improvement. With fast motion HD video such as live sports, images will almost always suffer from a certain amount of built-in camera smear, which can’t be processed away. For example, an HD image of a tee-off shot at a golf tourney will show the ball not as a round white object, but rather a smeared oval one as it finds its way sailing over the fairway. (I must give a shout-out to the HD camera operators who work their magic at golf tournaments and can uncannily follow the fast-moving ball as it soars through the air—these people are wizards in my opinion, and the same goes for cameramen who work their similar magic at hockey games).

Many of the high refresh video processors combine two functions into one, with only one of the two being desirable for some viewers. For fast motion HD video, these higher refresh rates employ “de-blur”, the technical term for the processing function that attempts to sharpen things up. For film-originated content, the video processor’s “de-judder” function attempts to smooth out the visual stuttering caused by the native 24 frames-per-second acquisition speed, almost always noticeable with any sort of horizontal or vertical camera pan. Some movie buffs object to the de-judder function’s post-processing visual result, which presents an image that many complain is too “video-y”.

And some of these schemes present noticeable artifacts as a result of the video processing in the form of occasional but noticeable picture breakup, including combing and tearing effects that are disconcerting. More than once, I’ve simply turned the high refresh function off and left it at that.

Fortunately, it appears that some of the newly-introduced LCD flat-panel models that feature high refresh rates are employing better-designed de-blur and de-judder video processing (a number of earlier models achieved their high refresh rate simply by inserting black frames in between the video frames). To do it right, sophisticated interpolation algorithms and suitably powerful processor chips are required to properly create new artifact-free inter-frames, and some recent LCD models appear to be superior with regards to the high refresh function, along with reduction of artifacts compared to past offerings.

An excellent example of who’s now doing it right would be the people at Samsung, who have recently developed their own in-house video processors. What sets the Samsung video processors apart is their ability to let users customize the amount of de-blur and de-judder processing separately, with individual controls for each function. With the Samsung approach, a viewer who wants sharper fast-motion video can adjust a dedicated de-blur control, while, if they prefer, they can turn down or even switch off the de-judder function entirely, if they’re put off by the film-smoothing effect.

Samsung is also to be credited for its new SD sharpening processor (a separate chip), which does a bang-up job of cleaning up SD video content that’s broadcast on a high definition channel. The processor actually has the ability to extract the original SD video signal from the HD video stream, and clean it up by improving the image sharpness and removing dot crawl and other SD video-related artifacts, and then re-scaling the image back to HD. I’ve seen it in action, both at a demo at Samsung’s LA lab as well as in my home, and I’m highly impressed.