Motion blur is a characteristic of displays that causes moving elements to appear blurry or to have a long trail following them (sometimes called smearing). There are a few elements of a monitor that cause motion blur, but one of the largest reasons is pixel response time.
The response time is the duration required for a pixel to change from showing one color to another. The slower the response time, the longer the trail following moving objects will be. Motion blur is important to consider if you use your monitor for watching sports or for playing video games since blurry motion can be quite distracting.
To test for motion blur, we take a picture to capture the appearance of the blur shown on screen as well as precisely measure the pixel response time using a specialized tool.
If you want to see our test for TVs, check our "Motion Blur of TVs" article.
Low motion blur is useful in almost all usages of a PC monitor since trails and blurry movements don't look natural and can often be distracting. However, some people might dislike monitors with low motion blur when watching 24p movies, since it can give the content a stuttery, jarring look.
While those users might prefer to have some motion blur, too much of it is an annoyance for most people. Long trails following football players or even video games that are too blurry to make out anything can be distracting enough to deter the user from enjoying that activity entirely.
To accurately capture the appearance of motion blur, we use the Pursuit Camera test methodology developed by Mark Rejhon of Blur Busters. It consists of a test pattern moving transversally and a camera placed on a rail that sits parallel to the screen.
While physically tracking the test pattern with the camera (the logo moves at a speed of 960 pixels per second), we take a picture at a shutter speed of 1/15th of a second.
Part of the methodology is also a validation system which uses a series of temporal tick marks positioned below the logo. This technique helps create consistent and representative pictures of the blur created by the monitor.
The second picture in our motion blur test is our response time graphs. These charts are based on data that is produced by our own multipurpose tool which uses an array of photodiodes and an Arduino Due connected to our test computer via USB. To test for response time, we display a series of grey slides on the monitor, and place on the display our photodiode tool. While the sequence of grey slides appears on-screen, the tool continuously captures the light intensity coming from the display. This allows us to calculate the time it takes for the pixel to transit from displaying one shade to another, thus giving us a response time measurement.
To produce a representative value, we measure 12 transitions in total. Going from 0% grey (absolute black) to 100% (absolute white) and a few steps in between, as well as an inverse for every step, since most displays take less time going down in intensity (100% to 0%, for example).
We then process the data and chart individual transitions, calculating the time to complete 80% of the transition as well as the time it takes to complete it entirely.
This test represents the average time in milliseconds required for the pixels of the monitor to complete 80% of a transition. This is one of the most important aspects of motion blur since it describes how long it takes for the majority of the image to appear which greatly affects the sharpness of moving images.
Our 100% response time test represents the average time it takes for a pixel to fully complete its transition from one frame to another. This helps determine the length of the trail left behind moving objects.
This test notes the monitor's setting which provides the best motion blur performance within our test without having too much overshoot. This is the setting at which our test results are captured.
While our motion blur test is centered around the response time, the general cause of motion blur is what is called "Persistence". Essentially, the longer a frame is kept on screen before switching to the next one, the blurrier a moving object will appear on-screen. While response time is a good way to reduce persistence, it is greatly affected by other aspects of the screen such as its refresh rate as well as the monitor's ability to use a flickering backlight (also called black frame insertion, BFI, or ULMB) which reduces the time a frame is shown.
This is why a screen that has an almost instant response time like an OLED TV can still look blurrier than a 120 Hz monitor that has a few milliseconds of average response time (if the content's framerate can match the refresh rate). While the transition time might be instant, the lower amount of "steps" for motion requires our brain to do additional compensation leads to blurrier movement. We've made a series of videos which explain the different aspects that affect motion which you can find on our Youtube channel.
Motion blur is particular to every display panel, but there are a few settings that might help you get better results.
Motion blur is a generally undesirable effect that causes motion to looks less sharp. It appears on essentially every monitor, but some have far less of it than others. It is generally best to have as little of it as possible. An important part of motion blur is the response time, which is the amount of time in ms necessary for a pixel to change from displaying one frame to another. However, other aspects such as refresh rate and image flicker can also affect the amount of blur that appears on-screen and are important to consider when shopping for a monitor that produces little motion blur.