Manufacturers like to emphasize the refresh rate (Hz) when specifying a TV. But how important is this refresh rate really? What type of TV should you choose? We explain it briefly.
When you’re looking for a new TV, all kinds of terms and names come to mind. One specification that is often highlighted in TVs is the image refresh rate, also referred to as Hertz or Hertz. The higher the Hz, the better, you’d think. But is this really the case?
50Hz, 60Hz, 100Hz or 120Hz
Let’s clear up some confusion first. In Europe we mostly talk about 50Hz and 100Hz TVs, and in the US we talk about 60Hz and 120Hz TVs. The reason for this is simple: the European grid’s AC frequency is 50 Hz, and in the United States it is 60 Hz. In the past, TVs had a refresh rate that was specially adapted to avoid all kinds of problems with image display.
However, modern TVs can handle both standards and use 50Hz and 60Hz refresh rates. More expensive models can also handle 100 and 120 Hz. To avoid confusion, we will only talk about 60Hz and 120Hz in this article.
Blurry images on the TV screen
You know the phenomenon: In an action movie, everything happens so fast, but it’s hard to see any details. Not because it happens so quickly, but because you get the impression that everything has become a bit blurry. You can also see the same effect during a football match, when the ball flies across the screen and also appears a bit blurry. How does this actually happen? There are two reasons for this effect, the so-called pixel response time and the “sample and hold” mechanism. We explain both reasons:
Pixel response time
Pixel response time is the time it takes for a pixel to switch from one gray value to another color value. If this time is too long, you will see a faded afterimage of the previous image in the next image. This is especially important with LCD displays, because OLED displays have a very small pixel response time. However, OLED TVs also suffer from fast and blurry images.
Sample and contract
The second, and also more important, reason is the TV screen’s “sample and hold” mechanism. All current television sets use this mechanism. It means that the image is placed on the screen and remains on the screen until the next image is displayed. Let’s take the ball during a soccer match as an example. A quick pass sends the ball flying across the screen.
If the TV is displaying 60 frames per second (or 60 Hz), the ball is at the player’s feet in the first frame at the start of the pass. That image stays on the screen for 1/60 of a second. In the following image, the ball is a certain distance from the player’s feet. But our brain knows that the ball is moving and our eyes follow the expected path of the ball for 1/60 of a second. So we moved our eyes, while the ball was stationary on the screen. This makes the ball appear to have a vague outline. Are you still following? On the website www.testufo.com/eyetracking you can see a simple but clear demonstration of the problem and how it works.
Higher Hz for better performance
Now that we know the reason, it’s also easier to understand the solutions. The shorter the image on the TV screen, the less our eyes move between two frames and therefore the less clear it is. That’s why high refresh rates are important.
A TV with a 120Hz refresh rate is less affected by this effect than a 60Hz TV. You can compare this improvement to a camera capable of taking many pictures per second. This way he can freeze fast-moving objects in time.
Create more frames using frame interpolation
But if the incoming video signal has 60 frames per second, such as sports footage, or even 24 frames per second, such as movies, does it matter that the monitor can refresh the image at a higher frequency such as 120 Hz?
It depends. If you ask the TV to display movie images as accurately as possible, it will display each image five times. In this way it creates 120 images (5×24), which are then displayed at a rate of 120 Hz. But of course this does not improve the sample and keeps the problem described previously.
To take advantage of the 120Hz display, the TV must calculate and display four new images between each of the original 24 images. This technique is called frame interpolation or motion interpolation. This way you take advantage of the 120Hz display. However, when watching films, some find that kinetic interpolation detracts from the original atmosphere that the filmmaker wanted to create. The image can then resemble the so-called soap opera effect.
Choose what you like most. For sports, the TV only needs to generate one intermediate image to go from 60 fps to 120. For sports, always choose frame interpolation mode. You can turn this on or off separately on most TVs.
Are you looking for a new TV? You should pay attention to this
The longer the image remains on the screen, the blurrier the image becomes. Another solution might be to simply set the image to black for a certain period of time. This technique is called “black frame insertion”, which is a black screen insertion. This technology is still used, but it has the side effect that you may see image flickering, especially if that black image is inserted at 60Hz. This can be very annoying. If inserted on a 120Hz monitor, the flicker is barely visible or invisible and looks as if you are making the image less bright.
What is the best option?
If you mainly watch sports and want to play flashy action games, choose a 120Hz TV. If you mainly watch TV series and movies, it depends on your preferences. If you hate motion interpolation, you’re better off using a 60Hz display. A 120Hz display can make your movie watching experience smoother and more detailed, but it may have the drawback that some movies look different than the filmmaker intended. Not everyone is happy about that.
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