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 the response time of the pixels. A slow response time leads to motion blur with fast-moving objects, black smearing in dark scenes, or ghosting when there's overshoot.
We test for the response time of monitors by taking a picture of a test pattern, then using a specialized tool that measures the response time for different transitions. We also check to see which overdrive setting is the best.
If you want to see our test for TVs, check our motion blur of TVs article.
The response time is the amount of time it takes for pixels to change from one color to the next. When there's constant movement on the screen, like in movies or games, the pixels are always changing colors, so having a slow response time results in motion blur. The faster the response time, the better motion should look.
A quick response time is helpful for most people using their monitor, especially for gaming and watching movies. It isn't as important if you're typing all day and there's less movement on the screen, but motion blur can also be noticeable while scrolling through documents or web pages. However, some people might dislike monitors with a quick response time when watching low-frame rate 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 video games that are too blurry to make out anything can be distracting, enough for some to stop watching the content altogether.
There are a few steps to measuring the response time of a monitor. First, we play a test video with a fast-moving object and take a picture of it. We then use a special tool that measures the response time while displaying different shades of gray, and software publishes the tables and graphs for it. Since most monitors have different overdrive settings, we check the response time and take a photo of each setting, and we publish the results of each, along with which is the best overdrive setting.
We measure the response time at the monitor's max refresh rate, including any overclock refresh rate, and at 60Hz. This gives us an idea of how it handles motion with a high-frame content versus a lower one.
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, and we take a picture at a shutter speed of 1/15th of a second. Part of the methodology is a validation system that 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.
Below you can see what good vs. bad motion handling looks like between the Gigabyte AORUS FO48U OLED on the left and the Lepow Z1 Gamut on the right. Keep in mind these are two very different types of monitors; the Gigabyte is a gaming monitor with an OLED screen, which are known for their near-instantaneous response time, and the Lepow is a portable monitor. We included the photos to show the obvious differences in motion handling between each.
The second part of our response time test is measuring the actual response time and publishing the tables. These tables are based on data 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 gray slides on the monitor and place our tool on the display. 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 pixels to transition from displaying one shade to another, thus giving us a response time measurement.
To produce a representative value, it measures 30 transitions between the 0% gray (black) to 100% gray (white) slides and other shades of gray in between, including transitions that go from light to dark. As you can see in the tables below, it starts with each of the gray values in the left column, and it transitions to the specified value in the top row to measure the rise/fall, response time, and overshoot error for each. The software calculates an average of each of the results to get the final result. Luckily, these tables are easy to read as they're color-coded, so you know what's good and what's bad. You can see below that the monitor on the left has a much better response time solely based on the fact that the tables are greener than the monitor on the right.
The rise/fall time tells us the response time from 10% into the transition until 90%. For example, if the screen is transitioning from pure black (0%) to pure white (100%), it's measuring the time it takes to go from 10% gray to 90% gray. The same concept is applied even if it's going from 60% to 80%; it's measuring from 62% to 78%. This response time is good when there are incomplete transitions, like when an object transitions from one color to the next so fast that it doesn't have time to make a full transition. In the tables above, the rise/fall time is represented in the top table, and you can see that the software automatically calculates the total average of all the transitions, which gives us our final result.
The total response time is the total amount of time it takes for the monitor to make a full transition. This number is also important for motion handling, but it's more important than the rise/fall time for slower-paced games because colors have the opportunity to make a full transition. This is represented by the middle table, and once again, we show the average time with the box on the right.
Overshoot error is the percentage of which the monitor goes past its target color, hence the name overshoot. So if the monitor has to transition from 20% to 80% gray, it overshoots if it goes past the 80% target. The percentage is a percentage of the target, not the difference, so if it goes to 85% for an 80% target, it overshoots by 6.25% and not 5%. Overshoot often happens when you set the monitor to its fastest overdrive settings because the pixels are trying to transition so quickly that they go past their target. In simple terms, if you're driving too fast, you'll likely stop past the stop sign.
You can see below an example of overshoot with the ASUS ROG Strix XG27AQ. In the chart on the left, you can see that the pixel transitions way past its target, with an overshoot error of 236%. This is because it's the strongest overdrive setting for this monitor, and you see in the motion photo that there's ghosting behind the logo because pixels are overshooting way too much.
We also measure the same rise/fall and total response time with just dark transitions. We consider dark colors between 0% and 40%, so we take six measurements into consideration here: 0-20%, 0-40%, 20-40%, 40-20%, 40-0%, and 20-0%. Like with the original rise/fall measurement, this one is also the time it takes from 10% to 90% of the transition. You can see the dark average rise/fall time next to the table. This result is important if you tend to play dark games or watch movies with dark scenes.
Once again, we measure the dark total response time using transitions between 0% to 40% gray. This is important if you play games with dark scenes.
We repeat the overshoot measurement for dark transitions. It may be easy for a monitor to overshoot dark transitions because there's room to overshoot, as you can see with the ASUS ROG Strix XG27AQ. However, this usually happens when you use the strongest overdrive setting.
If a monitor has multiple overdrive settings, we check to see which one is the best. We repeat the response time tests with all the overdrive settings, and we include a table in the text with links to all the tables, graphs, and motion photos. There are a few factors we consider when choosing the recommended overdrive setting, like the response time and overshoot error. We'll also compare the motion photos side-by-side if we're not sure which setting to recommend. Often, monitors of the same brand will have the same recommended setting because the companies make those settings the best, but it's not always the case. As with any recommendation, these are just guidelines, and you can choose any setting you prefer.
While we measure the response time at the max refresh rate, we also do it at 60Hz. This is important for some console gamers or if you have 60 fps games on your PC. Generally, motion looks worse at 60Hz because of the lower refresh rate, but it doesn't mean it has a worse response time. You can see in the photos below from the LG 27GP83B-B, whose 60Hz response time is one of the best we've tested, that motion still looks a bit more blurry than at its max refresh rate of 165Hz. We also check to see which is the best overdrive setting, and on many monitors, it's different than our recommended setting at the max refresh rate.
Although we don't publish the response time graphs as a photo like we do with the tables, we include a link to them in the text. The response time graph gives a visual representation of the response time and overshoot. Below are examples of the graphs from a monitor with a fantastic response time on the left (LG 27GN800-B) and one with a bad response time on the right (Samsung C27RG5). These are only for a few transitions, but you can see all their graphs by clicking the links below. The graphs are easy to read; the x-axis is the time, and the y-axis is the luminosity. All transitions start at 0 s, and the blue line shows how quickly it gets to the target or how much it overshoots it by. The LG is a lot quicker than the Samsung, especially with slow transitions, and even though it has a bit more overshoot, motion looks a lot better on the LG.
While our motion blur test is centered around the response time, the general cause of motion blur 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's greatly affected by other aspects of the screen, like its refresh rate and the monitor's ability to use a flickering backlight (also called black frame insertion), which reduces the time a frame is shown.
It's 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 that explain the different aspects that affect motion, which you can find on our YouTube channel.
The type of panel the monitor affects the response time and motion handling. OLEDs are known for their near-instantaneous response time because they can turn individual pixels on and off, but that may result in some stuttering because each frame is held on for longer. OLEDs are more common with TVs anyways, but they're becoming more common with monitors.
As for LCD panels, the TN and IPS types are considered the best with motion handling. TN panels were the king for that for many years, but as IPS panels have become more common in monitors, most of the monitors with the quickest response times that we've tested have an IPS panel. VA panels normally have slower response times in dark transitions than IPS and TN panels, leading to black smearing. However, some monitors with VA panels compensate for this with the overdrive settings, which improves the dark scene performance at the cost of overshooting in bright scenes. This doesn't mean that a monitor with an IPS panel is automatically better than one with a VA panel, but generally speaking, IPS panels have better motion handling than VA panels.
Motion blur is particular to every display panel, but there are a few settings that might help you get better results.
There are a few different factors that contribute to the motion handling of a monitor, and the response time is an important one. The response time is the amount of time it takes for pixels to transition from one color to the next, and a slow response time can lead to motion blur. It's also possible to have a response time that's too quick, so it overshoots its target color, creating a ghosting effect. We measure the response time using a special tool, and we check to see which overdrive setting is the best on a monitor, if it has one. This test is important if you watch content with many fast-moving objects or if you play video games.