Update Frequency
This term refers to the number of times per second that a video screen renews the displayed image. The higher the refresh rate, the more fluid and natural the movement. The basic standard for this reference was established in the last century with film projectors showing 24 frames per second (expressed in frequency in Hertz or Hz) and televisions with a frequency of 60 Hz in the United States and 50 Hz in many other countries. The 4k 60fps demo videos in this section have 60 real frames.
But with the advent of high definition, TV manufacturers have embarked on a race for refresh frequencies to go up to 120 Hz and even 240 Hz. There was even a period when some plasma TVs announced 600 Hz.
Following this logic, in the era of Ultra HD TVs, one would have expected 480 or even 960 Hz to flourish! However, most Ultra HD / 4K TVs sold over €1,000 operate at best at 120 Hz and achieve this by using 4K 60fps or more software techniques making the movements much smoother. The cheapest models do not exceed 60 Hz.
What about TVs with a refresh rate of 240 Hz or more?
Does this mean that those who traded in a Full HD 1080p 240 Hz TV for an Ultra HD model lost in terms of picture quality? As always, the answer is not so simple and straightforward.
Actual 4K 60fps update rate
The actual refresh rate quantifies the number of times the TV changes the picture on the screen. Traditional TVs do this 60/50 times per second, hence the expression “60 Hz / 50 Hz”. Some TV models can operate at a higher frequency, typically 120 Hz (120 frames per second) and 240 Hz.
Are higher rates synonymous with better picture quality?
This is the case with LCD and Oled TVs, which are the two dominant technologies. A high refresh rate can help reduce “motion blur” or kinetic blur.
What is kinetic blur?
All LCD and Oled TVs are affected. This occurs when an object that moves across the entire screen or image becomes blurred and softer than it was when it was set. In fact, this blurring effect is mainly the result of our brain. The latter detects motion and deduces where the object (or overall image) will be in the next fraction of a second. The problem with today's LCD and Oled TVs is that they fix each frame for sixty-fifty percent of a second when the brain thinks it should move. It creates motion where it is actually a series of still images.
The kinetic blur is caused by television, in addition to the blur created by the camera itself. Some viewers are not disturbed by this effect, others don't even notice it. But some are sensitive to it. The refresh rate is only part of the solution
However, doubling or even quadrupling the same images does not significantly reduce kinetic blur. We need something else.
Methods to reduce kinetic blur.
The first is interpolation. Television creates new images that are hybrids between two consecutive images. This can attract the brain efficiently enough not to erase the image. But depending on the intensity of the interpolation, this makes the image much more fluid. So much so that movies can look like TV movies. Film lovers tend to hate this effect. On the other hand, it is quite effective for retransmission.
The second option is the BFI (black frame insertion). This method turns off all or part of the TV's backlight. This has the effect of not freezing the image in such a way that the brain does not jam it. Inserting a black screen between two images allows the eye to refresh its vision. If not done correctly, this subterfuge can result in a shaken image.
The following is required to perform interpolation or CIB:
At least a 120 Hz refresh rate. A rate of 240 Hz is even better, because the backlight may flash faster and you may have more fineness for interpolation, as you have three new images to create instead of just one at 120 Hz.
But the 120 Hz refresh rate is really a minimum to counteract kinetic blur. All Ultra HD TVs on the market today are compatible with the 4k 60fps demo format and have values of 60 or 120 Hz. If this statement surprises you, especially if you've just bought an Ultra HD TV, it's because manufacturers are very “creative” about the terms of the refresh rate, as they were with Full HD TVs.
If the high-tech world is used to ambiguous specifications, that doesn't justify it. The update frequency is something specific, measurable. If a mark announces 120 Hz, the TV is legitimately expected to show 120 different pictures per second. If this is not the case, then it is for example a TV compatible with 4K 60fps can offer a movement effect similar to that of 120 Hz TVs, but it is not real 120 Hz.
As many, if not most, of the refresh frequencies seen on Ultra HD TVs are somewhat misleading. Despite the announced figures, no TV exceeds 120 Hz and many are only 60 Hz.
If you see elaborate nomenclatures such as “TruMotion 240 Hz” or if the technical data sheet does not explicitly mention the update of the screen, the figure announced does not correspond to reality. The few manufacturers who talk about soft drinks on their websites are very specific about what the screen does, the role of backlighting and image processing.
