Motion blur that you see on TVs influences how blurry fast movement appears to be on the screen. For the most part, motion blur manifests as a trail on moving objects, and is of particular importance for sports and video games. If you enjoy watching either of those things, it’s important to get a TV with minimal blur.
When evaluating motion blur, we photograph the appearance of blur on the TV, and then test for pixel response time and overshoot time.
When it matters
For the majority of TVs, motion blur is really only a potential problem with sports and video games, because of the quick movement inherent to both. With movies and regular TV, you will almost never perceive motion blur other than that which is included in the video, due to the low frame rate and the slow shutter speed of the camera.
Too much motion blur is very noticeable, and can ruin the look of movement on a TV – nobody wants a long trail following a moving object. Beyond those TVs that clearly have way too much blur, the amount of blur that a person will find acceptable is subjective. Some people are much more sensitive than others.
To provide an idea of the way motion looks on the TV, we use a rail-mounted pursuit camera to take a photo of our logo while it moves across the screen. The resulting photo represents what you can expect your eye would see while watching a moving object, and while it’s not a perfect representation, it’s at least a fairly useful example.
In the test, our logo moves across the screen at a speed of 960px per second, and at a frame rate of 60 fps. We slide our camera along the rail at the same speed as the logo, and take a picture with a shutter speed of 1/15 of a second, to capture all artifacts.
To validate that our camera goes at exactly the same speed as our logo, we are using temporal tick marks placed just below the logo. This technique was invented and proposed to us by Mark Rejhon of Blur Busters, a website dedicated to the reduction of motion blur.
You can test your own screen using our test pattern. If you follow our logo with your eyes, you will be able to compare it to our test results. Alternatively, you can find a wide variety of motion tests over at TestUFO.com.
Response time is the amount of time it takes a TV’s panel to change from one color to another, and it’s a pretty big part of the blur we see on TVs. With a long response time, the pixels can’t quite keep up with moving objects, and so you can see a lengthy trail of blur following behind them. Above, you can compare a long response time (left) to a short response time (right), and you can see that the difference is a pretty big one.
To test for response time, we use a Rigol DS1102E oscilloscope and a photodiode to record how quickly a TV is able to make transitions between different shades of gray. Every shade corresponds to a different level of luminance output, and so when a TV switches from one shade to another, the screen’s luminosity must also change. The amount of time it takes a TV to make this change in luminosity is the response time, which is measured in milliseconds.
Once we have performed this evaluation for each of the transitions we test, we take the times for each completed transition and average them out, which gets us our global response time number. Note that some transitions may have a lower response time than the average we list, meaning less blur for those changes, and others might take a good deal more time, creating more blur in those cases.
In the chart above, a transition between 20% gray (dark gray) and 80% gray (light gray) begins at the first vertical green line and is complete at the second vertical green line. The luminosity level of 20% gray is represented by the horizontal red line at the left, and that of 80% gray by the horizontal red line at the right. The time it takes the luminosity to change from the first to the second represents the length of the response time.
You can see that the transition between shades/luminosities is not a smooth line, but rather has leaps and dips, including a couple of jumps where the luminosity reaches (and even surpasses) the level required by the shade, and sooner than our response time measurement would indicate. However, those jumps are just temporary fluctuations; the transition is only considered complete when the luminosity is stable at the new level.
‘Overshoot’ means a TV went too far in a transition to a brighter color, surpassing its target. It then needs to bring itself back down to the target level, which will take at least a few milliseconds. A shorter overshoot time is better, and as with response time, longer overshoot times will result in lengthy trails on moving objects.
Overshoot exists because some manufacturers try to improve response time of transitions to lighter colors by applying ‘overdrive.’ This means that the TV’s panel tries to brighten at a really fast speed. If this is implemented well, the TV will use this boost to transition quickly, but will stop itself before it can surpass its target brightness. If it does not correct itself in time and passes its target brightness by, the TV has overshoot.
Our overshoot test is conducted in the same manner as our response time test.
The chart above illustrates overshoot on the 80% to 100% transition. The initial moment the TV exceeds the desired luminosity is marked by the first vertical red line, and the moment that it manages to return to and remain at the correct luminosity is marked by the second. The time (in milliseconds) that elapses between the two represents the length of the overshoot.
Elements of motion blur
Motion blur is created by several things:
- Response and overshoot times, which represent how long it takes a TV’s pixels to change from one color to another. Longer times equate to longer blur trails on moving objects.
- Frame time, which represents the amount of time for which a frame is displayed on the screen. The longer the frame time, the more blur you will see. See more information about this manifestation of motion blur here.
- Blur within the video itself. This results from the on-camera action outpacing the camera’s shutter speed. Cinematographers usually keep this kind of blur in mind, and will account for it when planning shots for the movie or show. The result will usually be that you don’t even register that the blur is there.
How to get the best results
Most elements of motion handling are static. For example, response and overshoot times can’t be changed through settings, and so those elements of motion blur cannot be improved.
If you have the option to do so, watching media with a higher frame rate will help you avoid blur. Some TVs may also have a couple of settings that can improve other elements of the motion blur, though you should be aware that they each have their own downsides. We list those setting below.
- Motion interpolation enhances the frame rate of video by creating and inserting transitional frames between the original video’s existing frames. This reduces frame time and creates a smoother look overall, but some find the result undesirably similar to the look of a soap opera. What’s more, since there is no improvement to the response time of the pixels, the length of the trail on moving objects doesn’t change. We talk more about the pros and cons of motion interpolation here.
- Some TVs have the option to introduce backlight flickering, or insert black frames, in order to shorten frame time and clarify movement. This also has the effect of dimming the maximum luminosity, though. As with motion interpolation, this does not affect response time, so the length of the trail on moving objects does not change. See more information about the effects of flicker here.
- By nature of the technologies, LCD panels (LCD and LED TVs) have relatively long response times, and OLED panels have much shorter ones.
- A video with a higher frame rate will only have less blur than an identical video with fewer frames if the TV’s refresh rate is capable of matching that frame rate (ex: a 120 hz video on a 120 hz TV, not on a 60 hz TV).
- Similarly, a TV with a 120 hz refresh rate will not have less blur than a 60 hz TV if the video’s frame rate is not also higher than 60 hz. With 60 hz video on a 120 hz TV, the video signal will still only be 60 fps, which means the frame time has not changed. The same applies for 24 hz and 30 hz on TVs with higher maximum frame rates.
- Refresh rate also does not have any effect on response time.
- It’s impossible to compare response times listed by different manufacturers and reviewers without knowing the testing methodology. We test several gray-to-gray transitions and present an average, but some manufacturers and reviewers will only list the shortest response time the screen is capable of, or they might test the time it takes to go from one shade to another, and then back. Unless you can compare the entire methodology, the results won’t match up in a fair way.
Motion blur makes fast movement look less clear, which can be an annoyance for sports fans and gamers. If you watch either of those things, it’s important to get a TV with minimal blur. To get a good idea of how much blur TVs have, we test them for their pixel response and overshoot times.
Your best bet for getting a TV with little blur is to find a model with low response time. You can also help reduce the amount of blur you perceive by watching higher-frame-rate video, or by enabling motion interpolation or backlight flickering features. Just remember that enabling these sorts of extra features can introduce other issues to the video.