HD Guru’s Glossary Of Developing Terms
Video technologies and products are advancing so rapidly these days that it’s easy to find yourself swimming in a sea of alphabet soup trying to keep up with the latest terms and abbreviations.
In an effort to bring things down to basics, we’ve decided to start a glossary of terms that our readers can use to refer to any jargon they might find they had forgotten or missed altogether.
It’s our aim to keep this up to date as new names and references come along, and we invite readers to contact us with any terms they’d like to see added for greater clarity.
To get started, the following are some terms we’ve found ourselves using more and more in recent months:
See our glossary of terms after the break:
3D Look Up Tables (LUT) are used extensively by the motion picture industry in the movie production chain to map one color space to another. LUTs are commonly used to calculate preview colors for a monitor or digital projector to see how an image will be reproduced on another display device. A 3D LUT is a 3D lattice of output RGB color values that can be indexed by sets of input RGB color values. Each axis of the lattice represents one of the three input color components and the input color thus defines a point inside the lattice. The most common practice is to use RGB 10-bit/component log images as the input to the 3D LUT. Output is usually RGB values that are to be placed unchanged into a display device’s buffer.
4K Ultra High Definition TV is a display or video format with 3840×2160 picture resolution that is four times greater than the Full HD 1080p standard (1920×1080 pixels) for HDTVs. At the end of 2012, the first flat-panel 4K UHDTVs became available. Under characteristics established by the Consumer Electronics Association (CEA) 4K TVs must include video processing that upconverts lower-resolution sources to 4K.
8-Bit Color is a palette of 256 shades of possible colors that can be used by an 8-bit television display, which represents most HDTVs and Ultra HDTVs available now. The current HDTV broadcast system is 8-bit, meaning there nearly 256 shades possible for each color or 16.7 million potential colors (256 green x 256 blue x 256 red).
10-Bit Color is a palette of 1,024 shades per each primary color offering more than 1 billion colors. This fills in shades between the colors in 8-bit systems brining greater depth and a sense of reality. With 12-Bit Color 4,096 shades and over 68 billion colors are possible.
The Advanced Television Systems Committee 3.0 (ATSC 3.0) is a next-generation television broadcasting system under development by members of the ATSC for eventual use in transmitting digital television signals over the air in the United States. Eventually, the system will bring a wide range of features for television programming viewed both by stationary receivers in the home and on mobile devices. Among the benefits proposed are 4K UHD and eventually up to 8K resolution images, high-dynamic range, a wide color gamut, 3D video, 3D object-based immersive audio, high frame rates, interactivity and over-the-air broadcasting to mobile devices as well as to the home and office. The signal will also be more robust, overcoming multipath interference issues experienced today and will provide the ability to reach inside thick walled structures and be received by devices moving at a high rate of speed. Because ATSC 3.0 is likely to be incompatible with current broadcast systems, it must provide improvements in performance, functionality, and efficiency significant enough to warrant implementation of a non-backwards-compatible system.
Chroma subsampling is used to reduce the amount of data in a video signal with little visible impact on image quality. Video created with chroma subsampling includes brightness information, with no color information. Color information is shared among adjacent pixels. The number of pixels that share the same color information is determined by the type of chroma subsampling. To describe the extent of subsampling, video professionals use a numerical shorthand that references a block of 8 pixels, 4 across and 2 high.
This is expressed as three numbers separated by colons. The first number indicates how many pixels wide the sample is (usually 4). The second number indicates how many pixels in the top row will have color information, or chroma samples. And the third number represents the number of pixels in the bottom row with chroma samples. Common examples include: 4:4:4, where every pixel gets a chroma sample with no subsampling necessary; 4:2:2, where every two pixels in the top row have to share a chroma sample, and every two pixels in the bottom row have to share a chroma sample (50% compression of color); 4:2:0, where every two pixels in the top row share a chroma sample, while the bottom row has no color information of its own, and has to share the chroma samples of the top row. Approximately, 75 percent of the color information is dropped. Most TVs and next-generation Ultra HD Blu-ray players will use the 4:2:0 system.
Color Gamut is all the color that’s possible for a TV or TV signal to create. Currently the smallest amount of colors available on HDTV and Ultra HDTV screens is represented by a triangle covering about 35 percent of the visual color spectrum. The colors in this triangle are known as the “Rec. 709” color space. Expanding the color gamut brings more shades of colors to the display from the natural world. Spaces beyond the Rec. 709 color space, such as larger triangles known as Digital Cinema Initiative-P3, representing just over 50 percent of the visual color spectrum, and Rec. 2020, covering more than 70 percent of visual colors, are referred to as wide color gamut, because they are wider than the current Rec. 709 standard. New advanced TVs and source devices like Ultra HD Blu-ray players are now being developed to support a wide color gamut, many of which fall just short of the DCI-P3 standard.
Deep Color is a color resolution standard for HDTVs and video products that include HDMI 1.3 connections or later. Deep Color supports 10-bit, 12-bit and 16-bit color bit depths, up from 8-bit, which is the current standard for consumer video. A higher color bit depth enables finer gradations between different shades of the same color, for smoother gradients and reduced color banding. Deep Color offers TVs the potential to display billions colors, but will require content that has been specially produced through every link in the video production chain and special hardware on which to play it.
Electro Optical Transfer Function (EOTF) describes how to turn digital code words into visible light. EOTF was originally determined by cathode ray tube (CRT) technology. The EOTF must match the reference display used by the artist to create original program.
Frame rate is the rate at which video or film frames are displayed. The frame rate for movies on film is 24 frames per second (24 fps). Standard NTSC video has a frame rate of 30 fps.
Full-array LED backlighting is a back panel illumination system for LCD TVs that places light emitting diodes (LEDs) across the entire backside of the LCD panel. Full-array LED is the best system of illuminating an LCD TV because light is evenly dispersed across the picture, and limits the amount of blotchiness on screen where sections of the screen receive different amounts of light than others in edge-lit or direct-lit LED systems. Full-array LED TVs are usually also accompanied by a local dimming system that enables dimming or entirely shutting off LEDs in some areas of the picture to produce greater contrast and black levels, which serves as the foundation of producing richer colors.
“Green UHD” and “Green Plus UHD (G+UHD)” are new LED systems developed by Samsung and LG, respectively, that add a White subpixel to Red, Green and Blue LCD panels to create a lower-cost Ultra HD LCD TV, although the actual resolution is closer to 3K. Most such products have been marketed primarily in the China market to date, also some 55- and 65-inch models have appeared for sale online in the U.S. under LG’s UF6800 series.
HDCP (High-Bandwidth Digital Content Protection) encryption is used with high-resolution signals over DVI and HDMI connections, and through the latest HDCP 2.2 iteration for 4K Ultra HD content, also supports the HDMI 2.0 and HDMI 2.0a interfaces. HDCP 2.2 can also be used to protect other high bandwidth digital video connections including DisplayPort, superMHL. USB Type-C and others. HDCP is used on the input and output jacks of TV displays and source components to prevent illicit duplication or distribution of protected programs without securing the proper copyright permissions. In order to play HDCP 2.2 protected video on a 4K Ultra HDTV, every link in the home theater chain needs to support the standard.
High Dynamic Range (HDR) has been around for years in still photography to produce detail in settings using a wide range of light. Photography uses combined layers of several photos of a subject taken at different exposure settings to bring out details normally lost in areas of darkness and bright light. Only recently has it been possible in digital motion picture cameras capable of capturing up to 15 f stops of dynamic range, which is the range from the “blackest” blacks to the “whitest” whites. It was possible to capture HDR in film in the past, but not in digital production until recently. Digital display devices including TVs, monitors and projectors, have also lacked the ability to produce HDR until new technologies emerged including organic light emitting diode (OLED) panels and LED-LCDs using quantum dots (also called nanocrystals), LEDs coated with new phosphor combinations, laser backlighting and other approaches. These various technologies enable either the display of an infinite black level (OLED) and/or a boost in brightness (LED) to widen the contrast range. Standards are still being determined for the exact luminance range for HDR enabled televisions.
Local dimming is a feature found on some LED-backlit TVs enabling them to dim or even completely shut off different sections of the LED backlight to produce deeper levels of black. These TVs can accurately display both light and dark portions of an image at the same time, for greater contrast and a more lifelike picture, and are often used in next-generation LED TVs supporting high dynamic range (HDR) capability.
Organic Light Emitting Diode (OLED) is a display technology used in mobile devices by many manufacturers and select high-end flat and curved screen TV displays, currently only available from LG Electronics. An OLED panel employs a series of organic thin films placed between two transparent electrodes. An electric current causes these films to produce a bright light. A thin-film transistor layer contains the circuitry to turn each individual pixel on and off to form an image. The organic process (called that because compounds contain carbon molecules) is called electroluminescence, which means the display is self-illuminating, requiring no backlight. OLED panels are thinner and lighter than current LCD HDTVs and produce the deepest black levels available on a consumer display.
Orthogonal Frequency-Division Multiplexing (OFDM), which is used for TV broadcasts today in parts of Europe and elsewhere, is a frequency-division multiplexing (FDM) scheme used as a digital multi-carrier modulation method proposed for the next-generation ATSC 3.0 over-the-air TV broadcast system for the United States. It is optimal for mobile reception because it uses a large number of closely spaced orthogonal sub-carrier signals to carry data on several parallel data streams or channels. It’s also much better at penetrating buildings and being received with fewer interference issues, because it will involve placing multiple transmission towers in a given city or market instead of just one.
x.v.Color (xvYCC color space) is a high-definition video color space launched in 2007 that is supported by certain HDTVs. Most of these models also include HDMI 1.3 or newer inputs. The x.v.Color standard supports 1.8 times as many colors (a wider color gamut) as the Rec.709 color space selected for the HDTV standard. In order to see the benefits of x.v.Color specially encoded content is required in addition to both a display and a playback source device supporting the technology.
By Greg Tarr
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