BenQ Knowledge Center

How is Monitor Response Time Measured?

BenQ
2020/08/21

To get good gaming experiences on a monitor, you need fast response times. How can you tell? Look for GtG and MPRT specs. A really good gaming monitor will have 1ms or close to that in both. Here’s why. 

Response time represents one of the most vital specs for monitors and all displays. Working in tandem with human eyesight, response time determines primarily how coherent an image will appear to viewers, whether it will have artifacts like blur, ghosting, or “trailing”, and how responsive interaction will feel. The latter’s extremely vital for gaming. Poor response time piles up onto overall input lag and may make playing video games unbearable. While a fast monitor can’t control lag induced by controllers, cables, and sheer distance, at least it takes care of business on its end.
 

Manufacturers like BenQ measure monitor response times using two primary methods. The more popular and objective approach is GtG. The more nuanced method is known as MPRT. We’ll look at both and try to help you figure them out. If you want a TL; DR, you really should look for a monitor with under 4ms in both tests. The closer you get to 1ms, the better. A 0ms monitor is something that keeps getting mentioned, but with current understanding of physics is effectively impossible. Unless we learn how to exceed light speed, there has to be some lag. 

Grey to Grey: Here to Stay

You’ve been seeing GtG response times for two decades now. Grey to grey measurements offer the most accurate and closest to hardware level indication of monitor response time. They tell us how long it takes a pixel to change from one grey value to another grey value. This method is popular because pixels are actually transistors or processing elements with multiple layers. The basic layer controls greyscale and is closest to the monitor’s processing core and power delivery, so to speak. So grey to grey will be the fastest response, which of course looks good in marketing materials, but is also the most honest and simplest to measure – and thus the most accurate.

Why not red to green or blue to red? Because colors are handled by upper levels of pixel transistors and the ways of producing them vary greatly among monitors, even within the same brand or the same series. Some monitors handle color in groups of pixels, others add quantum dot layers to enhance colors. All of those throw off response times. A monitor may have 3ms red to green but 5ms green to green, depending on which values of red and green we’re talking about. That would make reporting a comprehensible response time nearly impossible, unless you want companies to give you a PDF longer than War and Peace.

 

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Conversely, greyscale changes are uniform, so if it’s 1ms from grey X to grey Y, it’ll also be 1ms from grey Y to grey Z. Importantly, GtG reporting doesn’t count any post-processing or enhancements and isn’t readily subject to framerate. It’s a measure of the monitor’s response time on a very basic level, hence the utility attached to GtG reporting. If we’re being completely honest, GtG offers the most reliable specification pertaining to response time. Good gaming monitors routinely go below 4ms GtG, and many approach 1ms.

MPRT: In the Eye of the Gamer

MPRT stands for moving picture response time or motion picture response time. The test measures how long a pixel remains apparent or visible on the screen. The longer a pixel stays visible, the more blur or trail a moving image creates. The famous flying saucer test you may have seen showcases this. As the craft moves across the screen, pixels turn on and off to pass it from the left of the display to the right and back again.
 

A fast monitor with good processing capabilities and power delivery handles pixel activation and deactivation quickly, making the saucer appear as if it’s moving very neatly on screen, with no residue left behind.
 

Note we said appear. Unlike GtG, MPRT is very subjective. Sensitivity to blur and ghosting differs tremendously among individual people, just like with light sensitivity or motion sickness. An MPRT figure of 5ms means the average pixel on the monitor remains active for 5ms each time it’s turned on. For some, that may be superfast. Others may notice some blurring.
 

Also, MPRT is almost entirely dependent on framerate, whereas GtG has far less to do with framerate. A 1ms GtG pixel works essentially the same on a 30Hz TV and a 144Hz gaming monitor. But with MPRT, technically the minimum time for pixel duration is determined by refresh rate. So a 144Hz monitor has a minimum MPRT of 6.9ms (1/144th of a second). Then how can the same monitor offer 1ms MPRT? Because MPRT is so subjective and malleable, it’s also possible to improve it with good technology.
 

Just like framerate or refresh rate, with effective enhancements the MPRT performance of a monitor goes well beyond basic physics. Black frame insertion, clear motion, overclocking, motion enhancement, framerate control…these are all ways to boost motion on a monitor and eliminate blur and ghosting.
 

When done right, it’s very possible to achieve low MPRT. That’s what separates regular monitors from really good gaming monitors. Remember that while subjective, MPRT is overall better than GtG when trying to anticipate ghosting and blur. GtG gives us a definite number for overall response time, but lacks subtlety, which is what MPRT is for. Subtlety, sadly, often comes at the cost of subjective experiences. 

So Which One?

If a manufacturer only provides GtG, that’s good enough. You should be at under 4ms for a good gaming experience. Ideally, look at monitors that offer MPRT measurements as well. A 1ms MPRT monitor from a good brand tells you that a lot of engineering has gone into motion control and image regulation on that model, so somebody there really cares about optimizing panels for gaming. It’s rare for non-gaming monitors to advertise MPRT. Its very presence in the specs says you’re dealing with gaming-minded designers, so that’s most assuredly a good sign. 

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