The Truth and Hype on 4K, 8K, UHD and HDR

Transcription

1 The Truth and Hype on 4K, 8K, UHD and HDR For Television Engineers and Media Professionals A Telestream E-Book, by Paul Turner 1

2 In this E-Book, you ll learn about: The future of screen resolution The evolution of screen resolution 20/20 vision High Dynamic Range (HDR) The SDR/HDR problem About the author Paul Turner started his career as an engineer at the BBC, and since that time has held engineering and senior management positions both in the USA and the UK at a number of broadcast manufacturers. As VP of Product Management, Paul leads Telestream s global product and market strategy efforts for the company. 2

3 The Future of Resolution The talk on and around 4K/UHD video has increased considerably recently. Specifically, many TV manufacturers have been proclaiming that this will be the year in which higher resolution screens will become the norm. This is similar to what was said about higher frame rate sets a couple of years ago even though at that time, the only video that could be watched at higher frame rates came from video gaming consoles. Whether or not that turns out to be the case, both customers and some manufacturers are using the terms 4K and UHD (TV) Ultra- High Definition TV interchangeably, and this is invalid. Although similar in concept creating/ displaying an image that is approximately 4x the resolution of HD the two terms are not technically interchangeable. What is UHD? UHD is a term that s been coined by the consumer electronics industry for this new high-resolution imagery. The image size for UHD is 3840 pixels by 2160 lines exactly 4 times the size of an HD picture (which is ). Twice as many pixels horizontally and twice as many lines 4x the size. UHD 3840 pixels 2160 lines 3

4 What is 4K? 4K is the term used by the professional video market to denote this higher resolution as currently used in film and TV production work. The image size in this case is 4096 pixels wide by 2160 lines, so it is slightly more than 4x the image size for HD. 4K 2160 lines In many cases, this slight difference in horizontal resolution doesn t matter, but be aware that a UHD TV set cannot display a 4K image without either throwing away 256 pixels on each line, or rescaling the image to fit. Neither of these is a good solution for critical visual monitoring. To monitor 4K material in a critical professional environment, you need a 4K monitor pixels Key Takeaway: UHD and 4K are not the same thing. UHD is 3840 pixels by 2160 lines. 4K is 4096 pixels x 2160 lines. 4

5 Ch-ch-ch-changes One thing we know to be constant is that there is always going to be change. We ve moved from black and white to color to digital to HD, in the constant desire to bring higher and higher fidelity images to the home. Scarcely have we gotten used to hearing about 4K and UHD and already some broadcasters are talking about broadcasting in even higher resolutions -- like NHK s stated intention to broadcast the 2020 Olympics in 8K. to the image (aka spatial resolution ), then I believe we are heading in the wrong direction. It seems to me that it would be wiser for us to work on making better pixels, rather than simply having more of them, which may, in fact, not produce a better perceived image at all. B+W Do these 4K and 8K images look amazing? On the very large screens that they re shown on, yes. Is it practical for home use? It s hard to be sure. Even the most elaborate home theater is a different environment from a booth at NAB. And content needs to keep up with technological capabilities. The industry found that out the hard way with 3D. If all we do is add more pixels 4K HD 8K 5

6 The thing we need to talk about here is the relationship between the resolution on the screen and the capabilities of the human eye. But before we begin, lets remind ourselves that TV isn t real it s a representation of what you might see if you were actually at the camera s location. Key Takeaway: Image resolutions on screens are potentially unlimited, but human vision is not. Any discussion of the costs and benefits of higher TV resolutions needs to take into account the limitations of the human visual system. As media professionals, we want to deliver the highest fidelity image we can, which translates to the greatest amount of picture information. But there s no point in preserving data that can t be seen. Remember: in that scene you re looking at, there would be infrared and ultra violet light present. But you can t see it, so we don t bother to transmit it. So let s begin by getting a deeper understanding of the mechanics and limitations of the human visual system. 6

7 20/20 Vision 20/20 measurement is a frequently used term, but few of us know the true meaning. It s pretty important to understand, though, as visual perception is highly variable. In reality, most everything we do in our industry is targeted at the image quality perceived by the average human with 20/20 vision. The term was coined by a Dutch visual scientist in the mid 1800s. In a book on vision, Herman Snellen introduced the idea of the optician s eye chart, in which letters of a certain size could be read at a specific distance by a person with normal vision. This definition said that such a person could resolve features that subtended an angle of 1 arc minute (1/60th of a degree) on the subject s retina. The standard size of the letters was calculated so that a normal person could read the letters at a distance of 20 feet. So, a person with 20/20 vision is someone who can read at 20 feet (the second 20 ) what a person with normal vision could also read at 20 feet (the first 20 ). 20 feet 7

8 Most people understand intuitively the 20/20 vision concept, but what about the maximum visual resolution for the human eye of 1 arc minute? What this means when it come to TV is that there is a fixed maximum viewing distance that you can be away from your screen and still see all of the detail that the screen is providing. Move further away than that distance, and your eye is simply not capable of seeing all of that detail. So if you re at that maximum distance (as calculated for 4k, for example), and you replace the screen with one that is producing 8k images, all of that new detail is completely lost to you. It will probably come as no surprise that you actually need to be ½ of the 4K max distance in order to see all of the detail in the 8K. The maximum distance for 4k image viewing is 3 screen heights, or somewhere between 5 and 6 feet away from a typical large screen. That means you have to be sitting just 2.5 FEET away from the screen to resolve all of the detail in an 8K image (again, this is assuming a screen size of somewhere around 60 ). That s just not practical! To be seated anywhere close to typical viewing setups in most homes, the screen would have to be over 10 feet in size again, simply not practical in most homes. Key Takeaway: The higher the resolution on a TV screen, the closer you need to be in order to see all the detail. Beyond 4K, it would be hard for most viewers in homes to appreciate the detail in an 8K image. 8

9 High Dynamic Range Fortunately, higher resolutions aren t the only way to make images on screens more striking and realistic. Another opportunity for improvements is enabled by the sensitivity of human eye to variations in brightness. Our human eye can resolve the wide range of colors and brightness found in the natural world, but the existing TV systems limit the amount of light that the display can produce to the range of nits (a nit is a measurement of brightness) to 100 nits for full white. In comparison, the real world can produce high brightness colors and luminance levels. For example, a 100 watt light bulb produces approximately nits and the highlights of a sunny day can easily exceed 100,000 nits. Cinematographers and Directors of Photography have to adjust aperture on their cameras to allow those bright colors to still fit within the available range of TV transmission. The same is true for the range of colors that can be reproduced ( color gamut ), which is again limited to what is referred to as rec 709 colors. This results in what is now termed Standard Dynamic Range (or SDR) images. This standard range was largely determined by the CRT technology that was available when the specs were written. 9

10 In the years since, display technologies have advanced considerably. They can now produce a significantly wider black to white range and reproduce a much wider set of colors. Today s displays are capable of producing images which are much more vivid and true-to-life and this is what is now referred to as High Dynamic Range (HDR) images. The displays themselves are only part of the story, however. Cinematographers/DPs must now set up their cameras to capture a much wider dynamic range, and the transmission and processing technologies, including color correction equipment, need to be capable of handling it as well. crush the dynamic range of the image, which goes against the whole point of HDR in the worst case, they may throw away bits, which will result in significant contouring. Key Takeaway: The wider brightness and color range of HDR offers a way to improve picture quality independent of resolution. In particular, processing equipment needs to be able to work on signals of 12 bits. Generally speaking, this means that these processing devices must have an internal video pipeline of 16 bits. If not, the resultant processing will 10

11 The SDR/HDR problem Despite all the promise of HDR, there is no single standard as yet for the format to be used for delivery of HDR material. In fact, the CEA has just recently announced the industry definition for HDR compatible displays themselves. A major obstacle in HDR adoption has been figuring our how a legacy SDR set should display an HDR signal. There are several approaches, some of which separate the signal into SDR images with a sidecar transmission that provides the additional information needed to recreate the HDR signal in an HDR display. Others use metadata to tell the SDR set what to do with an HDR signal. HDR is unlikely to achieve widespread adoption until this standardization issue is resolved. One thing that is certain, though, is that HDR is very much at the forefront of everybody s mind when considering new television technologies. You only have to see the images produced by a properly sourced HDR display to understand the impact this technology is going to have on TV viewing. In fact, a well set up 1080p HDR image will blow away an SDR 4K image in almost every respect. The next step is to standardize on the delivery format and EOTF/PQ (the HDR equivalent of Gamma) so manufacturers know what to design to. Standard Color Gamut Wide Color Gamut 11

12 At Telestream, we re deeply engaged in the industry s effort to develop standards like HDR. It s just one way we re working to be sure our customers always have access to the latest technologies. Delivering solutions that anticipate forthcoming standards is another part of that commitment. For example, our Vantage Media Processing Platform is engineered with an award-winning 16-bit video processing system and pipeline, so its users are effectively HDR ready. And for certain input/output configurations, they can already process HDR material today. Would you like to see how? Please ask for a free demo. 12

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