HDR is an abbreviation for High Dynamic Range.We all know what the word high means, so to explain what HDR is, we should make it clear that DR is the concept of dynamic range.Dynamic range is a technical term that mathematically describes the range of levels of brightness in a given scene.HDR makes bright areas of the image brighter and dark areas darker.
Application of HDR technology
The brightness range that the human eye can perceive is about 10-3 -- 106nit, and the instantaneous contrast range can be up to 10,000:1. Currently, the brightness of consumer LCD is generally about 300-400nit, and its brightness range is generally 2000:1.Therefore, the brightness resolution of the human eye is much higher than the current mainstream display equipment.And the HDR display technology is to improve the brightness range of the display, so that we can see more colorful images.
The brightness resolution of the human eye is much higher than that of current display devices
The realization of HDR technology is accomplished through different gamma curves. In addition, there are two conversion functions of HDR at present. One is the perceptive quantization technology led by the institute of motion picture and television engineers, namely ST2084.The other is HLG, led by the international telecommunication union, which USES the conversion of optical signals to electrical signals (OETF).
The HDR format debate may not exist at all
In fact, the birth of HDR is not a long time ago. On August 27, 2015, the consumer technology association of America announced the HDR10 standard. In a strict sense, HDR came into our life from that day.
HDR image
But HDR10 is not the only standard. There are four HDR standards: Dolby Vision, HDR10, HLG and Prime/ sl-hdr1.There has also been a war of words over the four criteria.Today we're going to talk about the format wars that have been raging before.First of all, Prime/ sl-hdr1 is a set of standards cooperated by Technicolor and philips, which belongs to the definition of transmission. We won't discuss it too much.Today we are mainly talking about Dolby Vision, HDR10 and HLG. For the differences of the parameters of these three standards, you can see the following picture.
Comparison of three standards of HDR
Let's talk about HLG first. In fact, the purpose of HLG launch is very simple, which is to simplify the production process of HDR.Both Dolby Vision and HDR10 follow the conversion of electrical signals to optical signals, so later content needs to be reworked.However, for 24-hour TV programs, if all the signals are coded with HDR, it will be a huge amount of work, which is obviously not realistic.Compared with Dolby Vision and HDR10, HLG converts optical signals into electrical signals, which means that HDR coding can be completed directly when shooting, and it does not require a lot of energy in the later stage.So HLG is very suitable for TV programs.In addition, we can see from the figure above that the HLG does not clearly identify the brightness range, but USES the elastic percentage, which provides a dynamic range of 1200%.Because of this feature, it is very useful for both old and new TVS.In conclusion, HLG is likely to become the mainstream format of HDR TV broadcast signal in the future.
HLG may become the dominant format for television broadcast signals in the future
The first thing we need to know about Dolby Vision and HDR10 is that they both follow ST2084, so they are really the same brother.But the Dolby Vision version produces HDR10, not the other way around.HDR10 is a freely licensed generic version with a color depth of 10bits and USES static metadata that is not SDR compatible.So HDR10 is a compromise made by standard-setters to take care of the performance of most devices.Dolby Vision USES the double-layer coding technology and adds an enhanced layer supporting HDR on the basic layer of SDR content, so as to achieve the purpose of SDR compatibility.So here we can say that HDR10 is a subset contained in the Dolby Vision.Dolby Vision provides more functionality than HDR10.
Here we can conclude that all Dolby Vision enabled devices can support HDR10 and there is no compatibility problem between multiple HDR formats.HLG is more suitable for TV signals than Dolby Vision and HDR10.So the previously heated format wars may not exist at all.
Experience the HDR technology
We've talked enough about HDR technology, but how does it work in practice?Not long ago, we had a comprehensive experience of SONY's vpl-vz1000 laser TV.This product has the function of HDR. In the field demonstration, we saw that the screen of HDR had a qualitative leap in brightness and color performance compared with the ordinary lake.You can see the picture below.
In the field display, HDR technology has been added with a qualitative leap in the screen effect
Of course, our live experience is more than just watching his live presentation.The HDR picture effect of vpl-vz1000 laser TV was shot live.As can be seen from the picture below, the left is the screen after HDR function is turned on, while the right is the effect without HDR function turned on.It can be seen from the figure that when the HDR function is turned on, the contrast of the picture is stronger, the details of the bright part are more prominent, while the dark part is darker, and the picture is more infectious.
HDR function on and off effect comparison (above is on)
In addition, I would like to share with you my own movie-watching experience of HDR.Some time ago, I watched spider-man: the return of the hero at dolby cinema.In actual viewing, first of all, Dolby Vision's images are much brighter than ordinary 3D images. In addition, it has to be said that after HDR technology is integrated, there is a significant improvement in contrast.
Brightness and color HDR future development focus
In the future, HDR will certainly become a new selling point for TV and projector manufacturers, but if it is only technically compatible with HDR, and cannot meet the requirements of HDR in terms of brightness and color gamut, the actual improvement will be negligible.
The key points of HDR screen effect are brightness and color
The development of science and technology makes our life better
In essence, HDR is a large expansion of the overall brightness range of the picture, which is not only limited to white brightness, but also involves other colors.Just like the color gamut we often mentioned, it is actually a three-dimensional space. When the brightness of all colors is increased, the whole color space can be greatly increased, but if only to improve the brightness of a certain point of color, it is not enough to drive the brightness of the space to increase.This is called the truth that affects the whole body.In the future, whether it is a TV or a projector, the most critical point to obtain a good HDR picture effect is the brightness output and color performance.The wider and brighter the gamut, the greater the true potential of HDR high motion.