Some LCD panels – especially from 2nd tier manufacturers and older generation models - have a tendency to blur images particularly during fast moving scenes in movies, sports, and gaming events. This is due to LCD pixels that remain lit between frames - leading to a sort of a sample-and-hold effect as a result of the relatively long time required by the liquid crystals to align themselves i.e. twist or untwist - to represent a new pixel state.
This twisting action of liquid crystals acts as a light valve that allows or blocks light emitted by the backlight source, from reaching the glass surface of the display panel in response to the driving video signal.
Even some older generation plasma displays have a similar tendency to blur images. In the case of plasma televisions however, the reason is 'phosphor-lag'; this would normally manifest itself mostly when a bright object is moving fast against a dark background. However, phosphor-lag on the latest generation plasma TVs has practically become a non-issue.
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In contrast to LCD displays, plasma televisions and CRT TVs have a virtually instantaneous response time.
This is mainly limited by the speed of their video processing engine rather than by the time it takes to fire the display phosphor; this is in the order of nano-seconds as against the milliseconds required for the liquid crystals to change state in LCD panels. In this respect, LCD panels still have a long way to go.
Yet, there is a further technical difference between the two technologies that renders plasma superior when it comes to pixel response time. Control of pixel intensity in a plasma display does not rely on the same drive process used in an LCD panel. In an LCD display, a minor adjustment in pixel intensity level is brought about by altering the drive signal in very small steps to adjust the twisting action of the liquid crystals, and which in turn controls the amount of light reaching the surface.
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Irrespective of the way LCD response times are being reported by TV makers, it remains a fact that LCD display manufactures have moved a great way towards closing the performance gap with plasma and CRT displays to eliminate motion blur in LCD displays. The advancements in LCD display technology have been such that it is extremely unlikely you will ever experience motion blur with any of the latest 60Hz LCD HDTVs. Mind you, we do see a lot of blurring during fast action scenes but this is always inherent in the source. In other words, it would look the same irrespective of whether you are watching over a 60Hz LCD, a 120Hz LCD HDTV, or a plasma TV.
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Judder is the resultant visual artifact leading to a jerky movement when film is transferred to video since you cannot really repeat every single frame in 24-frames-per-sec film-based content to appear an equal number of times on 60Hz video. As a result, some frames are repeated twice while others three times during the 2:3 pulldown process, with the 'dirty' extra frame appearing every fifth frame. Judder is most noticeable in scenes that incorporate slow camera pans or in scenes shot with a handheld camera. 120Hz is the lowest refresh rate that simultaneously allows both 24Hz film-based and 30Hz video-based programs to be displayed without the need to kick in 3:2 pulldown.
This means that what you get with 120Hz - when done properly - is a smoother action by eliminating judder. We say done properly as some of the first LCD HDTVs using 120Hz did exhibit a number of video artifacts that could be annoying.
In other words, 120Hz technology alone has got nothing to do with motion blur and all to do with judder!
And of course there's also Judder that's film based that can only be removed with video processers that create extra frames like Sony's Motionflow.
07-11-2009, 09:49 PM
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