UHD: In constant development
By Yeray Alfageme, Business Technology Manager Olympic Channel
About one year ago we at TM Broadcast reviewed the UHD environment and its situation back then. HDR, 4K, HFR, WCG were concepts that we examined. Now, a year later, we take a look at them once again and see how they have evolved.
We will begin by going over notions we reviewed last year.
Let us start with definition, namely 4K. It has been a while now living in an HD -1920 x 1080- world, but one of the components of UHD, albeit not a must, is 4K. UHD does not only entail a leap in definition, but it is indeed an important aspect in this sense. 4K means four times more definition as compared to HD, from 1920×1080 to 3840×2016, a whole quantitative leap.
Another important aspect is WCG (Wide Colour Gamut). We were in former times living within a limited colour space, Rec.709 o BT.709. Such space had been created based on the older CRT monitors, which were only able to display a very limited amount of colours. And nothing had changed ever since. UHD presents an expanded colour space, i.e. Rec.2020 o BT.2020, much wider in scope while still adopting the same “white point” concept for backward compatibility. Just in between both we have DCI-P3, oriented to current monitors.
A parameter that goes unnoticed until we watch a 4K image directly is frame speed, the so-called HFR (High Frame Rate). As definition increases, the human eye becomes more sensitive to noticing “errors”. One of these “errors” in a video picture is precisely that is not actually a video, but a sequence of frames. This becomes very noticeable in UHD if we keep a frame speed of 50-60 frames per second. That is why increasing the frame rate, normally doubling it, is a must, although the standard provides liberty in this aspect.
Screen size –permanently on the rise- also makes this defect visible, especially at the edges of the image.
And finally, we have the main character, HDR (High Dynamic Range). UHD’s great ‘Wow!’. Because we can quadruple definition, increase colour space, have more frames per second, but if we do not increase the luminance level of our image, the effort will not be worthwhile.
After some time -nearly 2 years- already with UHD images, we can definitely say that the real change is HDR. In fact, studies have been made in which both professionals and spectators prefer an HD HDR image over 4K SDR (Standard Dynamic Range). And this is something to bear in mind indeed. HDR is the feature that does make images more realistic, more similar to what we see in the real world, what makes us all prefer them.
In fact, this is the aspect in which the biggest progress has been made, more in particular in the home market. The ST-2110 standard sets a luminance range so wide that -as it happens with WCG- current monitors and TVs are not able to feature it in full. However, most cameras are able to capture the 14 diaphragm stops featured.
This has forced manufacturers of domestic appliances to “invent” standards aimed at unifying TV set offerings. A year ago we contemplated two standards: HDR 10 and Dolby Vision.
Dolby Vision, as its own name indicates, is the standard promoted by Dolby in the market. It is possibly the most advanced one but requires a specific chipset in both sides of the chain, which restricts its expansion.
Other manufacturers joined up in HDR10, a free standard setting minimum requirements that all TVs must meet to be regarded as HDR10 compatible. It has been gaining advocates, but as it is “worse” than Dolby Vision, it had to undergo a natural evolution: HDR10+.