TV motion blur explained (and why all the 4K TV solutions fall short)
Unfortunately, a 120Hz refresh rate isn't going to save us. Here's everything to know about TV motion blur and four largely unsatisfying ways to fix it.
Geoffrey Morrison is a writer/photographer about tech and travel for CNET, The New York Times, and other web and print publications. He's also the Editor-at-Large for The Wirecutter. He has written for Sound&Vision magazine, Home Theater magazine, and was the Editor-in-Chief of Home Entertainment magazine. He is NIST and ISF trained, and has a degree in Television/Radio from Ithaca College. His bestselling novel, Undersea, and its sequel, Undersea Atrophia, are available in paperback and digitally on Amazon. He spends most of the year as a digital nomad, living and working while traveling around the world. You can follow his travels at BaldNomad.com and on his YouTube channel.
TV manufacturers have been trying to combat something called "motion blur" for years. You may have noticed the blur before and not been able to put your finger on what exactly was so bothersome about it. Or you may be enjoying watching television in blissful ignorance, never even realizing that your TV looks soft. Sorry in advance for ruining your viewing experience, but there are a few potential solutions to consider. However, these methods often have side effects that, for many people, are worse than the cure.
Take the soap opera effect. Along with many movie fans, Tom Cruise hates this "solution" to motion blur, which can make films look buttery-smooth in motion, kind of like soap operas. TV makers created this effect to combat motion blur and often associate it with 120Hz refresh rates.
High refresh rates and motion smoothing are just the beginning. Numerous other anti-blurring technologies, including LED backlight scanning and black frame insertion, can be found on today's
. Learning the pros and cons of each should help you get a TV image you're happier with. Or at least, happier than before I ruined TVs for you.
Watch this: Four great 4K TVs for every budget
What is TV motion blur?
Motion blur is when anything on-screen blurs, becoming fuzzy and less distinct, when it moves. This can be a single object, like a ball or car, or the entire screen, as when the camera pans across a landscape.
I always notice it when there's a closeup of a face, and then the person turns away. One second you're seeing every eyelash and wrinkle, the next it's a blurry mess.
Some of this can be attributed to the lower frame rate of movies and most TV shows, which can result in a blur caused by the camera. There's nothing you can do about that. There's also blur caused by the TV itself, which, to an extent, you -- actually, your TV -- can do something about.
In the early days of flat TVs and displays, the culprit was often the slow speed of the liquid crystal elements that create an image on LCD TV. These days most LCDs are able to change their states fast enough that motion blur is caused by something else: "sample and hold."
LCDs -- and modern OLED TVs -- configure their pixels to show an image and then hold that image until the screen refreshes. With most TVs this means that for a full one-sixtieth of a second, the image is stationary on screen. Then the screen refreshes and a new image is held there for another one-sixtieth of a second. Some TVs have faster refresh rates, and in some countries TV refresh every one-fiftieth of a second, but the process is the same.
Your brain on LCD TV motion: The blur is in your head
Sixty still images every second is fast enough to exceed your brain's flicker fusion threshold. You don't see still images, you see fluid motion. However, your brain is working fast enough that it's expecting to see motion during those hold times. The images are held long enough that your brain assumes anything in motion is going to continue being in motion… but it isn't. It's actually stationary and then jumps to the next position, which is also stationary.
Your brain and eyes, expecting smooth motion, blur the object by moving to follow where it should be. The physiological reasons behind this are beyond the scope of this article, but the key aspect is that motion blur is in your head (isn't everything?), which is important when it comes to discussing how we get rid of it.
Today's TVs have a number of solutions for reducing motion blur, none of which is quite satisfactory. But your mileage may vary. Here are the pros and cons of four potential motion blur solutions.
1. Higher refresh rates: 120Hz and beyond
TV manufacturers have known about the motion blur issue for years. It's the main reason for higher refresh rates. Modern
max out at 120Hz, but in the 1080p days, there were models up to 240Hz (or 100 and 200Hz, depending what country you live in).
Higher refresh rates don't, in and of themselves, fix the motion blur problem. The images are still being held, and if you just double the number of still images to fit 60 into 120 you haven't really changed anything. You need something to change to, and that's when things get interesting.
2. Motion interpolation: What causes the soap opera effect
The processing in modern TVs can determine, with a surprising amount of accuracy, what happens in between two frames of video. For instance, if a ball is on the left side of the screen in frame A, and the right side of the screen in frame B, the TV could safely assume that if there was a frame between A and B, the ball would be in the center of the screen.
A 120Hz TV determines what this "AB" frame would look like, then inserts it between frames A and B. This means there are more frames to switch between, and less time "held" on each frame. This is called frame or motion interpolation. With video content like sports, a new frame is inserted between every original frame, and the result is less motion blur and greater apparent detail. With movies and scripted TV shows, however, there's a problem.
Nearly every movie and nonreality TV show is recorded at a frame rate of 24 frames per second. This goes back to when nearly everything was shot on film. Though the early days had a variety of frame rates, Hollywood settled on 24, and it has been that way for decades.
These days very few movies or shows are "filmed," but the digital cameras are set to record at 24 frames per second. This is perceived by the vast majority of people as "fiction." Consciously or not, people equate higher frame rates with either low-budget or reality recordings. News, reality TV, sports and so on all use higher frame rates, usually 30 or 60fps.
Interpolating frames increases the apparent frame rate, so 24fps content no longer looks like 24fps content, because when shown on these TVs, it isn't 24fps content. The interpolation effectively increases the frame rate so 24fps content looks more like 30 or 60fps. More like sports, reality TV or the content that gives this effect its name: the soap opera effect. That's where our friend Tom comes in.
Many people don't notice, or don't care, about the soap opera effect. Others, like Tom and me, can't stand it. The ultrasmooth motion is not just artificial-looking, but can be distracting and unpleasant. Most Hollywood creators hate it, too, because it isn't what the director intended for his or her creative vision. If they wanted to record at 48fps, they'd have recorded at 48fps, like Peter Jackson did with The Hobbit.
Fortunately, most TVs not only give you the option to turn it off, but let you adjust how intense the frame interpolation is. So instead of a created frame that's halfway between A and B, maybe it's only slightly different from A or slightly different than B. If your TV has this adjustment, it's worth playing with to see if you can find a setting that reduces motion blur enough that you're not bothered by it, but isn't as intrusive as the more intense frame interpolation modes are. Some even separate out the processing to reduce the judder caused by putting 24fps content on a 60fps display.
3. Black frame insertion
Fortunately for people who hate the soap opera effect, there's another method to reduce motion blur. The general term is black frame insertion, but this broadly covers a lot of different ways to produce a similar effect. At its most basic, and where the technique gets its name, what happens is, a black frame is inserted between the real frames.
This, too, has its history in cinema. Though filmed at 24 frames per second, movies weren't shown at 24 frames per second. This was slow enough that some people saw the flicker. Instead, each film frame was shown twice, with a shutter blocking the light in between. Some cinemas went even further, showing each film frame three times. This blanking was a simple way to give some of the "performance" of a higher frame rate without the cost of additional film stock.
With black frame insertion, there's less "hold" in the sample-and-hold. It fools your brain better into thinking there's smooth motion. Once again, however, there are a couple downsides.
When the TV spends half of its time showing a black screen, its light output drops. In many cases this trade-off is acceptable, as modern TVs are exceptionally bright. In other cases, not as much. I have a front projector, for example, and the BFI mode can make the image look very dim.
There's also the potential for visible flicker, as the TV essentially flashes on and off with the inserted black frames. CNET's TV reviews often find that the flicker from BFI is too intense to be worth the improvement in motion blur.
Like frame interpolation, black frame insertion has different implementations. Rarely would a TV with a BFI mode show a black frame for the same length of time it shows a real frame. It's also not necessarily a "frame" at all. All LCDs create light with a backlight. This backlight can also turn off for only a portion of the time the frame is on screen, which is one of the ways companies can claim their 60Hz TVs have a "motion rate" higher than 60.
Another method is a rolling or scanning backlight, where parts of the image go dark in sequence. The backlight might darken first in the top quarter of the screen, then middle-top, middle-bottom and bottom quarter. Rinse and repeat.
There are also levels of how "black" the black frame is. A 120Hz TV could insert a frame that's a duplicate of the previous frame, but darker. Not "black," just dimmer. There are pros and cons to this method, too. Not as much light is lost, but perhaps the motion doesn't seem quite as sharp.
As with frame interpolation, if your TV has different settings, it's definitely worth reading up on what they do and testing them out.
The only two flat-panel TV technologies available today, LCD and OLED, both suffer from motion blur. However, there is still one display technology that doesn't: DLP.
Currently only found in front projectors, Digital Light Processing uses millions of tiny mirrors that rapidly flash on and off to build an image on a screen. Some movie theater projectors use this technology. At home they're not that expensive. You'll need a screen, too, but they're not that expensive either. Getting a 100-inch "TV" for under $1,000 is easy. Many models are even cheaper.
However, there are several trade-offs. While modern projectors are very bright compared to older models, they don't hold a foot-candle to the average television. In a room with dark curtains, or if you watch TV mostly at night, this isn't an issue. I've used a projector as my main TV for over 15 years. I use blackout curtains in that room, however.
The other aspect is the overall picture quality. The better DLP projectors' pictures look good and are exceptionally sharp, especially with motion compared to other display technologies. They don't have the color depth or contrast ratios of other technologies, however. So the image won't "pop" like it does on, say, an OLED TV. HDR is basically in name only. It can read the HDR data, but because they're not bright and the
is poor, it's not going to look much different than non-HDR content.
If you loathe motion blur, though, this is easily the best option. I am a projector proselytizer, but it's definitely a lifestyle choice. You'd really, really have to hate motion blur for this to be the reason you switch.
Many new TVs, especially midrange and high-end models, have some adjustability in how they handle motion blur. Hopefully, if motion blur bothers you, you can find a setting that works for you without annoying the rest of the family.
I have long loathed motion blur, being far more aware and annoyed by it than my peers. Since I also hate the soap opera effect, the only current option for reducing motion blur on my current projector is black frame insertion. And after a few months… I turned it off. The trade-off of a dimmer picture, and a just-noticeable flicker, was no longer worth the better apparent detail.
I'm not telling you to just give up, fellow blur haters. If you've had your TV for a while and just can't get past the motion blur, definitely try the various settings mentioned above. If you've gotten a new TV, perhaps upgrading from an old plasma or DLP rear-projection TV, see if any of the settings give you relief. If not, give it a bit of time and see if you get used to it. Hopefully you will.