Ultra High Definition: More Pixels, Better Pixels and Why It Isn t Just a Fad

Transcription

1 : More Pixels, Better Pixels and Why It Isn t Just a Fad A Technology Insight Paper

2 Ultra High Definition (Ultra HD) video will be here soon. What do you know about it, and what do you need to know? Most people know that Ultra HD has a higher resolution than High Definition (HD), with roughly four times as many pixels. That s why the terms Ultra HD and 4K are often used interchangeably. Many people think that Ultra HD is just another term for 4K, but resolution is only one part of what makes Ultra HD such an impressive technology. Resolution is only one part of what makes Ultra HD such an impressive technology. Resolution matters, but other components of Ultra HD matter more- -especially for small screens or viewing distances where increased resolution might be less important. Here are the four Ultra HD technologies that you need to know about: More Pixels High Dynamic Range Wide Color Gamut High Frame Rate MORE PIXELS HIGH DYNAMIC RANGE WIDE COLOR GAMUT HIGH FRAME RATE 1

3 Technology Cycles in AV More pixels mean better definition. The resolution of a display is the number of pixels it contains. Historically, we referred to displays by their vertical resolutions (e.g. 480p, 1080p). With Ultra HD that is changing. Ultra HD incorporates 4K resolution, which refers to the horizontal resolution of a display instead. 4K displays have horizontal resolutions of roughly 4000 pixels. For the highestquality video, you don t just need more pixels you need better pixels. 480px 720px 1080px 2160px 720px DVD 1280px 720p 1920px 1080p 3840px Ultra HD (4K) The actual resolution of 4K screens varies. There are three main standards related to 4K and Ultra HD resolution. ULTRA HIGH DEFINITION 4K (UHD-4K) DIGITAL CINEMA INITIATIVE (DCI-4K) CONSUMER ELECTRONICS ASSOCIATION UHD Resolution 3840 x x x Aspect ratio 16:9 19:10 16:9 + Screens with more pixels can display more discrete pieces of information. All other things being equal, higher resolution screens can provide a better image with more clearly defined objects. Resolution on its own is not enough to guarantee the highest quality picture, however. For the highest-quality video, you don t just need more pixels you need better pixels. That s why Ultra HD is about more than just resolution. 2

4 High Dynamic Range shows details in high-contrast scenes. Have you ever been watching a movie like Batman Returns and noticed that for many scenes the majority of the screen just looks black? That s because you re not watching in High Dynamic Range (HDR), which would actually show detail in those big expanses of black. HDR combines different exposure levels, so dark areas of the scene can use low exposure and bright areas rely on high exposure. This prevents details from being washed out or lost in shadow, as would happen with traditional processing. HDR will be the most important-- and immediately noticeable--feature of Ultra HD. Here s an example of the same photo shot at six different exposure levels. Notice that each exposure highlights certain details while completely erasing others: (continued) 3

5 High Dynamic Range (continued) Compare those washed-out and shadowed exposures to the same photo using HDR: With HDR image processing and bright displays, screen images will look incredibly lifelike. (HDR and source images courtesy of Dean S. Pemberton) The HDR photo shows detail in the bright cathedral windows, just like a traditional low exposure shot would. Simultaneously, it shows detail in the dark rafters, which would be completely black in low exposure. Conversely, if the traditional exposure were set to capture detail in dark areas, the windows would be washed out. HDR corrects both of those problems by blending separate shots using different levels of exposure. HDR video is very similar to HDR photography, with multiple images captured simultaneously to illuminate dark portions of the shot while dimming bright areas. Pair this technology with a higher-brightness screen, and you can see the details in everything you watch. With HDR image processing and bright displays, screen images will look incredibly lifelike. In fact, these changes will make a much more visible difference than a simple change in resolution, and they will apply to any screen size. 4

6 Wide Color Gamut builds better pixels. Not all pixels are created equal. Even at high resolution, pixel color quality makes the difference between a clear and muddy image. To understand how pixel color works, we ll need to take a brief trip back to high school biology. The human eye contains cells called rods, which detect brightness, and cones, which detect color. For now we re concerned with color, so we ll focus on cones. There are three types of cone. Each is most sensitive to a specific range of light wavelengths (i.e. colors). They re called S, M and L cones because they respond best to small, medium and large wavelength light. Any given color of light will activate one type of cone more than the other types. A blue tone will activate S-cones far more than M- and L-cones, while a red tone will activate L-cones the most, M-cones somewhat and S-cones barely at all. No display is advanced enough to show all of the possible colors perceived by the human eye. Human color vision is made up of the possible blends of activation levels from these three types of cone. It s often represented on a graph like this: This is the CIE 1931 color space, and it s standard for defining the range of color values that the average human eye can see (continued) 5

7 Wide Color Gamut (continued) No display is advanced enough to show each one of these possible colors. (In fact, if you re reading this on a computer the colors you see in the colorspace are limited by your monitor s settings, and if you re reading it in print they re limited by the toner colors.) Each pixel in a display has a maximum value for its red, blue and green subpixels. When those are graphed on the color space, they create a triangle. Inside the triangle are all the color values that the display can show. This is referred to as the display s color gamut. Outside the gamut are colors that people can perceive in real life, but that cannot be shown on the display. Outside the gamut are colors that people can perceive in real life, but that cannot be shown on a display This is the srgb color gamut (standardized as BT.709), which is standard for CRT monitors and Blu-ray Discs The example above shows the srgb color gamut (standardized as BT.709), which is standard for CRT monitors and Blu-ray Discs. It covers about 35% of the spectrum of possible colors. In other words, your Blu-ray can only show 35% of the possible colors that your eyes can see. Dolby colorist Shane Ruggieri has a great analogy for working within the color limitations of current TVs: he says it s like writing a story using only part of the alphabet. (continued) 6

8 Wide Color Gamut (continued) Next generation technology will overcome this limitation. Ultra HD Blu-ray will use the BT.2020 color space. This is a significant improvement, displaying over 75% of all possible colors. Many Ultra HD TVs will adopt this wide color gamut, too. 0.9 It s hard to overestimate the added quality that comes with widegamut color This is the Ultra HD Blu-ray color gamut (standardized as BT.2020), which is is a significant improvement, displaying over 75% of all possible colors It s hard to overestimate the added quality that comes with wide-gamut color, and unfortunately it s impossible to display on screen or in print. While 4K resolution may only be visibly better on a large screen or at an unusually close viewing distance, wide color gamut is immediately recognizable and impressive. Seeing it demonstrated at trade shows, we thought this is why people will buy Ultra HD TVs: for the color, not the resolution. 7

9 High frame rate keeps images sharp. With more pixels, higher dynamic range, and more colorful pixels, Ultra HD is already an enormous improvement over today s HD displays. There s one final feature that will make a dramatic, visible improvement to the technology, though: High Frame Rate. High Frame Rate is what it sounds like. Rather than the film standard of 24 frames per second (FPS), HFR film uses about 48 FPS. For video, the numbers increase from about 60 FPS to at least 120 FPS. In still or slow-moving shots, it s hard to see a difference. In action sequences, the difference can be dramatic. Rather than the film standard 24 frames per second (FPS), HFR video supports much higher rates. It s often assumed that HFR reduces flickering. That s a misunderstanding based in problems associated with old film projectors, whose shutters physically blocked light between frames. Newer technologies like digital projectors use mirrors rather than shutters, and the light is nearly constant. Similarly, the backlight or sidelight on an LCD screen or the light of an LED is extremely high frequency and does not have perceptible flicker. What HFR does improve is the ability to show crisp images in motion without judder. Anyone who s taken a photograph knows that if your subject is moving and your shutter speed is slow, the picture will be blurry. That s why high-action shots often use extremely fast shutter speeds to maintain sharp images. When shown at a low frame rate, these sharp images can look juddery. This is where high frame rate comes in: it allows the use of extremely short shutter speeds while maintaining the look of smooth motion. You get sharply defined details without the jumpiness. Like the better pixels described above, this fast-pixel technology will look good on any size of screen. 8

10 Tying It All Together: The Full Ultra HD Package When customers buy Ultra HD, what they ll really be buying is this enhanced image package. Displays won t be replaced solely for the upgrade to 4K resolution, they ll be replaced for better color, more detail, and smoother motion. Ultra HD Blu-ray has released specs and is already setting the bar for other Ultra HD technologies. Content is here, and the entire market is poised to make the step to Ultra HD. Here s the question: does your Ultra HD solution have what it needs to get better pixels, not just more? Sandy Drive State College, PA videon-central.com9