The pixel response time (response times)
We now know that the response time should be at least on the level of the refresh window. It is better if the pixels finish their change from one color to the next faster than the next image comes. Otherwise there is the ghosting effect. If the pixels are very fast, thanks to the so-called overdrive (found in almost every monitor’s OSD), this does not immediately mean that there are no more artifacts. Pixel overdrive can lead to massive overshoot. And then you swap in the worst case: ghosting for inverse ghosting. That ultimately depends on whether the monitor manufacturer or display manufacturer manages the pixel overdrive well or only uses it to print the 1 ms response time on the packaging.
The picture illustrates what I have tried to explain to you. Inverse ghosting becomes noticeable from 15% average overshoot. Anything greater than 30% overshoot will be noticed even by a layman, and anything greater than 40% makes a game virtually unplayable. Maybe one or the other has already noticed it and thought that the monitor is broken. No, this is due to the overdrive setting or poor to no variable overdrive. But more about that later. First the question, what is the response time and where does the overshoot come from?
What is the shortest connection between two points? A straight line. In reality, the response time unfortunately looks different. For example, the start point is the color black (bottom) quasi parallel to the X axis (time in ms) and the end point would be the color white. In short, the response time is the time it takes a pixel to change from one color to the next. I think it is clear from the graphic and you can also see what exactly overshoot is. Here, the target color is overrun by x percent and this can be very noticeable under certain circumstances. If the overshoot only goes up for a very short time, then it is usually not so bad. The higher the peak and the longer it takes to get back to the actual target color, the more noticeable it becomes.
Here is an example measurement: Very fast response times, but an unbearable amount of overshoot = visible inverse ghosting! (Attention: This is the extreme case that should serve as an example here, the monitor from MSI can do better)
Example two: Not quite as fast response times, but still fast enough and you cannot notice any overshoot while gaming.
In this form you will be supplied with graphics from me in the future. How I do the whole fair, I explain to you in a separate article. I hope that the slides can be understood without explanation? Don’t forget, the response time of the pixels should be smaller than the refresh window and if possible – without significant overshoot!
Variable Refresh Rate (VRR) and Variable Overdrive
By now, everyone should know what VRR is. Most monitors and TVs support this via G-Sync or FreeSync. The frame rate is adjusted to the output FPS. Synchronized! We gamers find this very nice, because tearing is almost impossible with it. But image artifacts – mostly overshoot – can still occur in the form of inverse ghosting. Why? Because not every monitor supports variable overdrive. This ensures that the pixel overdrive is adapted to the FPS. As a rule, the response time is slower as the FPS decreases, since the frame rate also decreases.
The picture illustrates the whole thing quite well. The goal is for the gamer to set their monitor to the maximum refresh rate, enable adaptive sync, and set the best overdrive setting in the OSD. That would be the ideal state. This is exactly what I will always show you in my tests. Ex: A 165 Hz 1440p with FreeSync Premium and G-Sync Compatible
Is the monitor capable of variable overdrive or do you have to choose a different overdrive for 60 – 100 FPS games than for 100 – 165 FPS? Thus, for games that only reach up to 100 FPS on the screen – you might have to set the Normal setting in the OSD and everything above 100 FPS should then run with Setting Fast. Why? Yes, simply because otherwise you might get inverse ghosting in Fast Mode up to 100 FPS. Or you have blurr trails (ghosting) with Normal Mode at over 100 FPS. Nobody wants that…
Finally, the link to the panel types from the first part. Until about 2 years ago, only TN panels were able to implement 240 Hz with correspondingly fast response times in a really usable/gamable way. Today, however, there are a lot of IPS panels that can even do 360 Hz with really good response times. VA panels (currently only Samsung panels are known to me) are now also capable of 240 Hz in 1440p and 2160p. These Samsung VA panels are, in terms of response times, among the fastest LCD panels ever. But there is one type of panel that doesn’t even need the variable overdrive. An OLED panel doesn’t even know what overdrive is. They don’t need that, because they can actually do 1 ms response time and that without overshoot – no matter if 60 or 175 FPS are arriving!
So, now we know the response time and the frame rate. But what if the input lag is much larger than the pixel response time? What use is a 240 Hz display then? We will clarify this on the next page and send such statements into the realm of fables.
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