• Friday, August 23, 2019

Display refresh rate – what is it exactly?

Smartphone manufacturers are trying hard to improve the hardware of their phones, and fine-tune it as much as they possibly can to appeal to as many customers as possible. All hardware features are subject to these improvements, including displays. Display characteristics are measured in several different ways. We can talk about a display’s size, the resolution, type of a panel, but the thing that we’re the most interested in in this blog is the refresh rate.

What is the refresh rate?

The refresh rate, in its essence, signifies the number of images that are refreshed on the screen per second. The higher this number is, the smoother the image on the screen appears to be. The refresh rate is expressed in Hz (Hertz) units, which clearly means that it is basically just the frequency of changing the images on the screen.

In order to understand why the refresh rate is important, it is first necessary to understand the concept of refreshes per second. A digital panel, either LCD or AMOLED, works by firing up pixels. Movements on the display are perceived as shifts in the color of the pixels that fire up at any given time. The number of times per second that phone sends signals to pixels is exactly this refresh rate. This is how a screen displays an image. This is similar to the famous Mexican wave. The movement is seen only when people who were sitting down stand up, followed by the next group.

It is all fine and dandy until a screen is only displaying still images. But what happens to videos and other moving images, like rendered games?

Here it’s important to also understand the concept of frames per second. Similar to the refresh rate, it signifies the number of images sent to the screen. For example, videos are commonly recorded in 60 frames per second. This means that the refresh rate of the display that this video is shown on has to be at least 60 Hz in order for each frame to be sent to the display. This ensures the perception of a smooth image.

The most common refresh rate in modern phones is exactly 60 Hz. Sixty refreshes per second are plenty enough to ensure smooth transitions, and for the human eye not to really see these refreshes as they are happening too quickly.

Technology, as we know though, progresses at a fascinating pace. Camera sensors have become very capable, while smartphone games as well are becoming more and more graphically demanding. In this blog, we’ll use videos taken by a smartphone camera as an example in order to explain why companies are increasing the refresh rate of their screens as well.

Why is it important?

 

Cameras nowadays are well capable of recording slow-motion videos. These videos are recorded in 120 FPS, 240 FPS or even 960 FPS. The question arises, how to display more frames per second on a screen when the refresh rate is only 60 Hz? Slow-motion is realized by “stretching” the duration of the video in such a way to match each frame recorded by a camera over two refreshes of the screen. That way we can see fairly smooth slow-motion videos. This could be improved, though, by increasing the refresh rate of a display in order to once again have that 1:1 ratio – 1 frame to 1 screen refresh.

This is exactly what display manufacturers have tried to do! It is now becoming more and more common for phones to have displays with 90 Hz, or even 120 Hz refresh rate.

90 Hz displays

As we’ve said earlier, the refresh rate makes a huge difference in gaming and video displaying. It is no wonder that these displays are mostly implemented into gaming phones, but even some more mainstream ones have them implemented. Take for example the OnePlus 7 Pro. Its display has the refresh rate of 90 Hz, and virtually all contents look much smoother and much better than on a 60 Hz display. Obviously, this difference can only be seen when two displays are directly compared, however, it’s clear that the 90 Hz display simply reproduces the content much more nicely. Here is our review of the OnePlus 7 Pro, where you can learn more about this phenomenal phone and its display.

120 Hz displays

OnePlus has pushed the refresh rate of their flagship phone to 90 Hz, but ASUS has recently announced their new gaming flagship, the ROG Phone 2. This new phone’s display will have 120 Hz display, which means that it will be fully capable of displaying really smooth 120 FPS videos or game renders. In gaming, this is very important because each millisecond can be crucial.

A common question among smartphone fans is whether refresh rates of over 60 Hz even have a place on the market. We’ve already said that a naked eye can’t see beyond 60 Hz. There is an argument to be made for certain niche uses, like sporadic video editing on a phone, or competitive smartphone gaming that’s on the rise. Overall though, 60 Hz displays are good enough for an average user. Higher refresh rates are a nice feature to have, but they are definitely not a must as they don’t really do enough to justify the price difference that they cause.