Entering the era of 4K Ultra HD, many new terms have emerged, which I have gradually explained in an article the year before last. In particular, HDR has gradually been recognized by everyone. In fact, this term is not new. As early as the early 1990s, the first camera equipped with HDR was launched. In the field of photography, the development is still very fast. There are countless cameras and cameras equipped with HDR. Even in today’s mobile phones, HDR is not uncommon in lens sensitive elements. But in the field of TV and projection, with the development of 4K TV in recent years, it has gradually entered people’s field of vision.
Since 2016, the UHD alliance began to publish the specifications of 4K HDR home TV / projector, and the HDR standard has been set. At the CES exhibition in January of the same year, the announcement of UltraHD premium certification standard also indicates that 4K has really entered the era of standardization. Because of this, the relevant products of 4K HDR have also been published one after another, such as 4K HDR TV, 4K HDR projector 4K HDR Blu ray DVD and support 4K HDR power amplifier and so on.
UltraHD premium equipment certification standard:
1. Resolution: 3840 × 2160 pixels
2. Color depth: 10bit
3. Signal input: support bt.2020 (note that the current HdTV products can not completely cover the range of bt.2020 gamut, here only support bt.2020 signal input)
4. Color gamut: more than 90% dci-p3 color space
5. HDR: support SMPTE st2084 eotf high dynamic range image electro-optic conversion
6. Brightness dynamic range: (1) brightness above 1000 nit / Black bit below 0.05 nit (mainly for LCD)（ 2) Brightness above 540 nit / Black bit below 0.0005 nit (mainly for OLED)
But now HDR seems to have entered a period of confusion, because after the emergence of endless HDR standards, we are a bit confused. Hdr10 and Dolby vision HDR are well known by the public. However, it’s a bit confusing to know about HDR pro, hdr10 +, hdr400 / 600 / 1000 and so on. Therefore, I’d like to make a small topic here, so that you can really understand the things behind these standards from a deep level, so as not to be fooled when you buy HDR products.
What is HDR?
If you want to understand, you have to start with the basics. What is HDR? In short, HDR is the abbreviation of “high dynamic range”. Its full English name is “high dynamic range”. It belongs to a display technology. The corresponding display technology is SDR (standard dynamic range). The so-called dynamic range refers to the brightness difference in the image field. The larger the dynamic range is, the richer the bright and dark details are recorded simultaneously. HDR can express a wider dynamic range of brightness than SDR.
As can be seen from the above figure, HDR is closer to the actual image effect seen by human eyes, while SDR is lost in both the first and second images.
Generally, the range of brightness that the human eye can perceive is 10 ¹² cd/m ²， But the traditional display device can only display 10 ³ cd/m ²， However, HDR display devices can display a brightness width of 10 ⁵ CD / m ²， In other words, it can capture more than 100 times the brightness of traditional display devices.
As the next generation of high-quality image technology, HDR has attracted much attention. HDR related content has been seen in streaming media platforms such as Netflix and Hulu, as well as video services such as UHD Blu ray, such as the content of 4K UHD Blu ray discs provided by our website.
What are the terms of HDR?
In the environment of HDR display devices, there are many terms that need to be understood. Here is a summary:
1. Nits and stops
The brightness of the output light of the display device is measured in nits, 1nit = 1CD / m ²。 The brighter the brightness of the display device, the higher the nit number.
Taking the logarithm of 2 according to different brightness values, the value obtained in the image field is called stops. The figure below shows that from the darkest – 5 to the brightest + 5, it is said to have a dynamic range of 10 gears.
But the brightness of the display device is different from that of the real object you see. For example, the sun is photographed, and the real brightness of the sun is 10 ¹² Nit, but it’s impossible to really use 10 in a display device ¹² Nit to show, you see the brightness may be just outside the window brightness, about 10 ³ Nit.
2. What is dynamic range?
The so-called “dynamic range” is to display a bright range, so if you want to improve the “dynamic range” and be able to display it, the key point is to be able to achieve higher brightness.
As shown in the above figure, in the real natural environment, the brightness difference in a scene may be very large. For example, the brightest petal in the sun shining part can reach more than 10000 nits, while the brightness of the background is only 100 nits, which is 100 times different. In the past, in the traditional rec.709 display device, these colors and brightness can not be displayed normally, because the display range of rec.709 color and brightness is very small, so a broader color space is needed to accommodate more colors and brightness. At this time, rec.2020 is needed. So what are rec.709 and rec.2020? Now let’s talk about it in detail.
3、REC.709 、 REC.2020
In the previous display technology, the famous bt.709 (rec.709) standard defined the display range of brightness and color, while bt.709 (rec.709) defined the brightness according to the CRT cathode ray tube display at that time in the 1990s, from 0.1nit (CD / M) ²) To 100 nits (CD / M) ²)， The dynamic range is only 6.5.
When the display range of the image exceeds the range defined by bt.709, there will be highlight overflow and dark part cutting. In other words, it can not display more brightness details, such as high light dead white and dark dead black
Rec.2020 color space standard is the upgraded version of rec.709, which is also the color space of Ultra HD devices. For example, the current 4K display device and the future 8K display device can display more colors and a wider brightness range compared with rec.709.
In the figure above, the small triangle is rec.709, the large triangle is rec.2020, and the outermost part is the color range that the human eye can see. It can be seen that rec.2020 can present more colors and brightness than rec.709.
If you can’t understand the plane version, you can read the following three-dimensional version:
The brightness range of rec.709 is 0.1nit to 100nits, while the brightness range of rec.2020 is 0.0005nit to 10000nits. To put it simply, you can see almost endless black and almost the brightest light.
4. What is the peak brightness?
Today’s 4K HDR TV usually says “peak brightness”. So what is “peak brightness”? In fact, this is very easy to understand, that is, the maximum brightness that a TV can achieve, and this maximum brightness can determine the effect that HDR can present.
At present, for ultra high definition HdTV (uhdtv), the peak brightness of OLED panel must reach 500 nits, while that of LCD panel must reach 1000 nits. In fact, at present, many 4K HDR TVs with LCD panels have reached or exceeded 1000 nits, while OLED panels have not yet reached 1000 nits due to technical reasons (as mentioned in yesterday’s article on OLED, which will not be repeated). However, this does not mean that OLED brightness is very low, Actually, in the highest light part, it’s very eye-catching. Of course, it should be noted that any film and television work can not be presented with the highest brightness from the beginning to the end. At most, it is in some explosion and fire scenes that the highest brightness can be produced regionally (in theory, it can reach 4000 nits according to the requirements of hdr10, such as some scenes in bililyn’s midfield), which is basically harmless to the eyes.
Well, with so much basic knowledge about HDR, we will start to advance to a new knowledge point, which is also the most critical one.
What are the current HDR standards for home audio-visual equipment?
Home audio and video naturally includes HdTV, projector, monitor, player, power amplifier and other equipment. Let’s explain one by one.
The most basic standard is hdr10, which is the basis of HDR of all manufacturers. It is an open standard announced by the consumer Technology Association on August 27, 2015, and does not need to pay any copyright fee. This standard requires the use of wide gamut rec.2020 color space, 10bit color depth, and SMPTE St 2084 (PQ) image transmission function, but its data elements are all static, simply speaking, the output HDR image effect of each frame is the same. At present, all devices supporting 4K HDR must meet this standard, such as TV manufacturers such as LG, Samsung, sharp, Sony and Vizio, Microsoft’s Xbox one series game console, Sony’s Playstation 4 game console and Apple HdTV 4K. Of course, 4K UHD Blu ray and 4K UHD streaming media must support this most basic standard.
Here we need to explain that Sony’s Playstation 4 host does not support 4K UHD Blu ray video playback.
Dolby vision HDR
Dolby vision HDR is the most advanced HDR standard proposed and customized by Dolby laboratory. Different from hdr10, it is not an open standard and must pay a certain copyright fee (it is reported that it is $3 per device per year) to use it. Dolby horizon requires the use of wide color gamut rec.2020 color space, SMPTE St 2084 (PQ) image transmission function. Different from hdr10, it adopts 12 bit color depth and supports dynamic data element structure. Dolby horizon allows a maximum brightness of 10000 nits (currently only up to 4000 nits in the device).
At present, the HdTV that supports Dolby vision HDR includes some products of LG, Sony, TCL, Visio and other manufacturers, and the display and projector that support Dolby vision HDR have not appeared yet. Among the 4K UHD Blu ray machines, some products of LG, Sony, oppo, Philips, Panasonic and other manufacturers support Dolby vision HDR.
Hdr10 +, also known as hdr10 plus, was jointly announced by Samsung and Amazon video on April 20, 2017. Due to the extremely high copyright fees of Dolby vision HDR, Samsung and other manufacturers are unwilling to pay, so they have established hdr10 + alliance with Panasonic, Amazon and 20th century fox to promote hdr10 + standard. Hdr10 + updates hdr10 by adding dynamic metadata. Dynamic metadata can be used to adjust the brightness level of HDR more accurately on a scene by scene or frame by frame basis, similar to Dolby horizon HDR, but the color depth is still 10bit.
Hdr10 + video began to be provided by Amazon video on December 13, 2017. On January 5, 2018, Warner Bros. announced its support for hdr10 + standard and joined the hdr10 + alliance. On January 6, 2018, Panasonic announced the launch of 4K UHD Blu ray player supporting hdr10 +.
HLG is a HDR standard jointly developed by BBC and NHK. It is compatible with standard dynamic range (SDR) display, but it needs 10 bit color depth. HLG defines the nonlinear electro-optic transfer function (eotf), in which the lower half of the signal value uses gamma curve and the upper half of the signal value uses logarithmic curve. HLG standard is royalty free and compatible with SDR display. HLG is supported by HDMI 2.0B, hevc, VP9 and h.264/mpeg-4 AVC. HLG is mainly used in broadcasting and some streaming media, such as BBC iPlayer, DirecTV, Freeview play and Youtube.
The above four are currently the most mainstream HDR standards, which should end here. However, there are always so many accidents, because each manufacturer has made several customized logos, which makes people confused. For example
Anyone who uses this logo comes from the promotion logo of hdr10 given by LG. As early as 2016, when LG promoted its own products, such as the early 4K HDR HdTV such as LG 43uh6500, it would take this logo, but in fact it is still hdr10 in essence. Of course, now the new HDR TV will no longer appear this logo.
This logo belongs to Sony, which generally refers to their 4K HDR product line. All products marked with this logo support hdr10, or some products support Dolby vision HDR, such as Bravia a1e and a8f.
See here, dizzy, want to cry? Do you think it’s over here? did not! Because the monitor has created a new one