240Hz vs 120Hz LCDs – Are they worth it?

240Hz vs 120Hz LCDs – Are they worth it?

With the ever growing demand of flat panel TVs, manufacturers are coming up with new ‘improvements’ by the handful to keep prices high.  One of the most recent of these is the advent of higher refresh rate LCDs, promising the most ‘fluid’ motion yet as well as decreasing the appearance of strobing and blurring ‘problems’ slower panels produce.  The first improvement was bumping the rate from 72Hz to 120Hz.  Now they’ve gone a step further and have introduced 240Hz sets.  What the manufacturers aren’t telling you is how little this $200-$400 premium improves upon your viewing experience.  When it comes to 120Hz vs. 240Hz, the following can help you understand why it’s not going to make that much difference to your human eyes.

Without getting too technical, it’s important to explain a few fundamentals of motion photography, all of which affect whatever it is you’re watching (TV programs, DVDs, Video games, etc).

Shutter Speed
Motion pictures start with a single frame, a photograph, which is captured buy a shutter opening for a brief moment to allow light to land on a medium that exposes the image.  The medium can be film, a digital sensor, etc.  There’s much more going on, but what’s important to understand with shutter speed is that the time the shutter is open (usually a fraction of a second) directly affects the way it captures motion.  Slower shutter speeds will introduce blur, faster shutter speeds will create sharper clarity.

Frame Rate
This is the speed at which each frame is captured and is noted by ‘frames per second’ (fps).  As expected, this is the number of  still photographs that are taken in one second.  Most movies are shot at 24 fps.  Some at 30fps.  Most news, sports, and things that look like ‘video’ are shot at 60 fps.  A higher frame rate give a crisper detail while the cinematic 24fps gives a smoother more ‘movie like’ experience.  Even if that does not make sense to you, what’s important to understand is that anything you are watching on your TV is first and foremost affected by the way it was captured to begin with.  This is where TV manufactures mislead you the most.  Just as in the 720p vs 1080p HD arguments, it doesn’t make any difference what your TV can output, if the source material can’t deliver.

Refresh/Redraw Rate
So how does refresh rate come into play?  LCDs function by redrawing the screen a certain number of times per second.  This rate is is expressed in hertz (Hz). Hertz simply refers to the frequency or cycles per second.  Most initial LCDs performed at 60Hz.  This was undoubtedly due to the standard that CRTs have delivered for years.  Why 60Hz?  Basically, at the advent of television, manufactures and filmmakers determined through series of tests that most humans eyes and brains process visual information at a plateau of 60-70Hz (similarly frames per second).  Because much of the content original created for TV delivery was shot at 30fps or 60fps, it made sense to claim 60Hz as a standard as both divide equally into 60.  When 60fps source material is played, your 60Hz TV displays each frame once – 30fps footage has each frame displayed twice, one after the other.

Strobing
A problem, however, arose with this standard: how to display movies which are almost exclusively shot at 24fps ?  The solution was 3:2 pull down, the TV displays one frame 3 times, the next frame 2 times, the next frame 3 times, etc.  With 60Hz playback, this happens so fast that you can’t tell it’s happening in most cases.  The exception is when there is a lot of action going on in a scene which causes a phenomenon known as judder.  This judder or ’strobing’ effect is more a result of the source footage than that of the TVs refresh rate.  The reason being that the film you are watching was captured at 24 fps, and even though it is slight, the series of frames are often shot at a higher shutter speed (1/48 of a second is standard) than the matching 24fps (which would be using 1/24 shutter speed).  This means that there is a brief moment of time that the subject being photographed is not being recorded to the media.  In slower moving scenes and, more importantly, slower moving focal subjects this is hard to notice, but in faster moving subjects it’s more obvious.  With the large size of LCDs panels and their increased resolution, this problem became more apparent to image quality enthusiasts.

Motion Blur
The second perceived problem with motion video is blurring.  The visual aspect is pretty self explanatory – when subjects are moving fast (a running quarterback) or the camera is panning quickly the image’s clarity becomes smeared or blurred.  Theoretically, if the TV’s redraw rate is slower than the source materials frame rate, this would blur frames together – this, however, is not the most common cause of blur.  Most blur results from the shutter speed that the camera is using, as mentioned above.  If you’ve ever used your point and shoot camera with the flash turned off in a dark scene, you know this first hand as lights and subjects are smeared out of recognition.  This is an extreme example, but shooting at shutter speeds like 1/24 and 1/48 (very typical for film) and even 1/60 will create this effect, albeit at a lesser extent.  Without going into it too deeply, it’s mainly important to realize that once again it’s the source material (how the footage was captured) that’s going to introduce most cases of blur that the viewer is going to notice and has very little, if anything, to do with the redraw rate of the TV they’re viewing.

These issues, but mainly the issue of strobing, created the need for the first Hz bump to improve the playback of 24fps material:  72Hz LCDs.  This new rate was termed ‘native’ because it properly handled 24fps footage by displaying all 24 frames 3 times each (24×3=72).  These sets automatically determined the format of the source material and switched between 60Hz and 72Hz automatically and showed reasonable improvement when it came to displaying 24fps material vs 30fps or 60fps material.  This was a welcomed and worthwhile advance.

So as the pattern goes in commercial electronics, TV manufacturers started upping rates even further.  Next came 120Hz, essentially doubling the rate of original 60Hz models.  As you probably guessed, these sets display source material in the following rate/frame relations:  60fps – each frame displayed twice, 30fps – each frame displayed 4 times, 24fps – each frame displayed 5 times!  120Hz was the obvious next step because 120 divides so nicely for all frame formats, but as you can see – it’s really just displaying static frames more often.  The source frame itself is not improved upon, just redrawn.  And now we have 240Hz sets coming to market, which basically means you take the above relations and multiply them by 2.

You may finally be asking yourself, what does the redrawing of the same frame do to improve our two problems, judder and blur.  The answer is pretty simple – hardly anything if the source material is not improved upon.  You may see demos of text charts and shapes gliding across screens in your local B&M electronics store comparing the difference in performance of the various refresh rates.  While these may be visually convincing, they’re most likely running source material that is created (digitally, read: artificially) at higher frame rates and therefore will take advantage of the higher refresh rates these sets offer.  What they’re not doing is showing you material that 95% of consumers will be playing on their sets (DVDs, analog TV, Digital TV, etc).

So what does this mean?  It’s really a waste of money to pay the premiums on these TVs.  They offer such little improvement that you’re just wasting your money.  It’s like buying a car because it can reach speeds of 240 mph when you’re legally limited to 70mph.  The technology may be beneficial in the future(possibly down the road 2-5 years), but by then newer technologies will be available (don’t be surprised to hear of 480Hz next year) and 120Hz and 240Hz will be standard in even the value priced TVs.  Just as with HD video (720p, 1080p, 1440p), if your source content isn’t taking advantage of these new technologies, you’re not really gaining the benefits they can provide.  Until recording/delivery standards are raised to meet 120fps, or 240fps – you’re just not going to see the difference.  I have heard that some gaming consoles will be heading that direction (not surprising), but I can promise you that film & TV wont be there anytime soon.  The technology is certainly there, but broadcasting standards take far too long to make these transitions as we’ve seen so clearly with the 2 decade transition to digital broadcasting.

Save your money, buy a 72Hz LCD (or a plasma – another discussion all together) and be done with it.

Related posts:

1. 120Hz vs 240Hz – more info An article recently written over at displaymate.com provides more evidence...

Related posts brought to you by Yet Another Related Posts Plugin.

Tags: 120 hz, 240 hz, 60 hz, 72 hz, lcd, plasma, television

This entry was posted on Tuesday, August 18th, 2009 at 3:47 pm and is filed under General. You can follow any responses to this entry through the RSS 2.0 feed.