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103-523: Rec. 2020 is extended for high-dynamic-range (HDR) by Rec. 2100 , which uses the same color primaries as Rec. 2020. Rec. 2020 defines two standard image formats of 3840 × 2160 ("4K") and 7680 × 4320 ("8K"). These both have an aspect ratio of 16:9 and use square pixels . Rec. 2020 specifies the following frame rates: 120p, 119.88p, 100p, 60p, 59.94p, 50p, 30p, 29.97p, 25p, 24p, 23.976p. Only progressive scan frame rates are allowed. Rec. 2020 defines

206-496: A tristimulus colorimeter . Often a 6bit plus FRC panel is sold as 8bit and a 8bit plus FRC panel is sold as 10bit. FRC is no true replacement for more bits. The 24-bit and 32-bit color depth formats have 8 bits per primary color. With Microsoft Windows 7 and above the user can set the gamma correction through the display color calibration tool dccw.exe or other programs. These programs create an ICC profile file and load it as default. This makes color management easy. Increase

309-504: A "your scaling software sucks/rules" image based on this principle. In addition to scaling, the problem also applies to other forms of downsampling (scaling down), such as chroma subsampling in JPEG 's gamma-enabled Y′CbCr . WebP solves this problem by calculating the chroma averages in linear space then converting back to a gamma-enabled space; an iterative solution is used for larger images. The same sharp YUV (formerly smart YUV ) code

412-473: A WCG is used. The color dynamism and wider range of colors frequently attributed to HDR video is actually a consequence of a WCG. This has become a point of significant confusion among consumers, whereby HDR and WCG are either confused for each other or treated as interchangeable. While HDR displays typically have WCGs and displays with WCGs are usually capable of HDR, one does not imply the other; there are SDR displays with WCGs. Some HDR standards specify WCG as

515-467: A better match to the output device gamma is required. The sRGB color space standard used with most cameras, PCs, and printers does not use a simple power-law nonlinearity as above, but has a decoding gamma value near 2.2 over much of its range, as shown in the plot to the right/above. Below a compressed value of 0.04045 or a linear intensity of 0.00313, the curve is linear (encoded value proportional to intensity), so γ = 1 . The dashed black curve behind

618-409: A bit depth of 8 or 10 bits, HDR uses 10 or 12 bits, which when combined with the use of more efficient transfer function like PQ or HLG, is enough to avoid banding. Gamma correction Gamma correction or gamma is a nonlinear operation used to encode and decode luminance or tristimulus values in video or still image systems. Gamma correction is, in the simplest cases, defined by

721-399: A bit depth of either 10 bits per sample or 12 bits per sample. 10 bits per sample Rec. 2020 uses video levels where the black level is defined as code 64 and the nominal peak is defined as code 940. Codes 0–3 and 1,020–1,023 are used for the timing reference. Codes 4 through 63 provide video data below the black level while codes 941 through 1,019 provide video data above

824-412: A correctly calibrated system, each component will have a specified gamma for its input and/or output encodings. Stages may change the gamma to correct for different requirements, and finally the output device will do gamma decoding or correction as needed, to get to a linear intensity domain. All the encoding and correction methods can be arbitrarily superimposed, without mutual knowledge of this fact among

927-416: A default gamma to PNG images with metadata omitted. This made it impossible for PNG images to simultaneously match HTML or untagged JPG colors on every device. This situation has since improved, as most major browsers now support the gamma setting (or lack of it). A gamma characteristic is a power-law relationship that approximates the relationship between the encoded luma in a television system and

1030-465: A display’s capabilities are insufficient to reproduce all the brightness, contrast and colors that are represented in the HDR content, the image needs to be adjusted to fit the display’s capabilities. Some HDR formats (such as Dolby Vision and HDR10+) allow the content creator to choose how the adjustment will be done. Other HDR formats, such as HDR10 and hybrid log–gamma (HLG), do not offer this possibility, so

1133-521: A firmware upgrade that added support for the Rec. 2020 color space to their EOS C500 and EOS C500 PL camera models and their DP-V3010 4K display. On September 5, 2014, the Blu-ray Disc Association revealed that the future 4K Blu-ray Disc format will support 4K UHD (3840 x 2160 resolution) video at frame rates up to 60 fps. The standard will encode videos under

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1236-453: A gamma between 3 and 4 depending on lighting conditions. In LCDs such as those on laptop computers, the relation between the signal voltage V s and the intensity I is very nonlinear and cannot be described with gamma value. However, such displays apply a correction onto the signal voltage in order to approximately get a standard γ = 2.5 behavior. In NTSC television recording, γ = 2.2 . The power-law function, or its inverse, has

1339-591: A gamma of about 0.45 and decoded with the reciprocal gamma of 2.2. A notable exception, until the release of Mac OS X 10.6 (Snow Leopard) in September 2009, were Macintosh computers, which encoded with a gamma of 0.55 and decoded with a gamma of 1.8. In any case, binary data in still image files (such as JPEG ) are explicitly encoded (that is, they carry gamma-encoded values, not linear intensities), as are motion picture files (such as MPEG ). The system can optionally further manage both cases, through color management , if

1442-406: A higher-quality image source. It does not improve a display's intrinsic properties (brightness, contrast, and color capabilities). Not all HDR displays have the same capabilities, and HDR content will look different depending on the display used, and the standards specify the required conversion depending on display capabilities. HDR-TV is a part of HDR imaging , an end-to-end process of increasing

1545-426: A larger color space increases the difference between colors, an increase of 1 bit per sample is needed for Rec. 2020 to equal or exceed the color precision of Rec. 709. The NHK measured contrast sensitivity for the Rec. 2020 color space using Barten's equation which had previously been used to determine the bit depth for digital cinema. 11 bits per sample for the Rec. 2020 color space

1648-493: A laser allows for generating almost monochromatic light. The NHK stated that at the time it was announced this 4K LCD has the widest color gamut of any display in the world. On June 17, 2015, Digital Projection International presented a 4K LED projector with support for the Rec. 2020 color space. On January 4, 2016, the UHD Alliance announced their specifications for Ultra HD Premium which includes support for

1751-438: A license. The formats vary in their capabilities. Dolby Vision and HDR10+ include dynamic metadata while HDR10 and HLG do not. The dynamic metadata are used to improve image quality on limited displays that are not capable of reproducing an HDR video to its fullest intended extent. Dynamic metadata allows content creators to control and choose the way the image is adjusted. The HDR10 Media Profile, more commonly known as HDR10,

1854-416: A prerequisite of compliance. Regardless, when a WCG is available on an HDR display, the image as a whole can be more colorful due to the wider range of colors. More subjective, practical benefits of HDR video include more realistic luminance variation between scenes (such as sunlit, indoor, and night scenes), better surface material identification, and better in-depth perception, even with 2D imagery. When

1957-466: A slope of infinity at zero. This leads to problems in converting from and to a gamma colorspace. For this reason most formally defined colorspaces such as sRGB will define a straight-line segment near zero and add raising x + K (where K is a constant) to a power so the curve has continuous slope. This straight line does not represent what the CRT does, but does make the rest of the curve more closely match

2060-418: A voltage. In our CRT example 1/ γ is 1/2.2 ≈ 0.45. A color CRT receives three video signals (red, green, and blue) and in general each color has its own value of gamma, denoted γ R , γ G or γ B . However, in simple display systems, a single value of γ is used for all three colors. Other display devices have different values of gamma: for example, a Game Boy Advance display has

2163-519: Is DisplayHDR 1400, which was introduced in September 2019, with monitors supporting it released in 2020. DisplayHDR 1000 and DisplayHDR 1400 are primarily used in professional work like video editing. Monitors with DisplayHDR 500 or DisplayHDR 600 certification provide a noticeable improvement over SDR displays, and are more often used for general computing and gaming. (Brightness in cd/m ) (Color gamut) Color depth (Brightness in cd/m ) (Number of video frames) UHD Alliance certifications: HDR

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2266-409: Is a newer format that is similar to Dolby Vision, but is royalty-free. HLG is a broadcast HDR format that is used by some TV broadcasters. Before HDR, improvements in display fidelity were typically achieved by increasing the pixel quantity, density (resolution) and the display's frame rate. By contrast, HDR improves the perceived fidelity of the existing individual pixels. Standard dynamic range (SDR)

2369-403: Is a straight line, with slope everywhere equal to gamma (slope is represented here by the derivative operator): That is, gamma can be visualized as the slope of the input–output curve when plotted on logarithmic axes. For a power-law curve, this slope is constant, but the idea can be extended to any type of curve, in which case gamma (strictly speaking, "point gamma" ) is defined as the slope of

2472-501: Is a technical recommendation by ITU-R for production and distribution of HDR content using 1080p or UHD resolution, 10-bit or 12-bit color, HLG or PQ transfer functions, full or limited range, the Rec. 2020 wide color gamut and YC B C R or IC T C P as color space . SDR uses a gamma curve transfer function that is based on CRT characteristics, and is used to represent luminance levels up to around 100 nits. HDR uses newly developed PQ or HLG transfer functions instead of

2575-439: Is a technology that uses high dynamic range (HDR) to improve the quality of display signals. It is contrasted with the retroactively-named standard dynamic range (SDR). HDR changes the way the luminance and colors of videos and images are represented in the signal, and allows brighter and more detailed highlight representation, darker and more detailed shadows, and more intense colors. HDR allows compatible displays to receive

2678-429: Is an HDR video format announced on 20 April 2017. It is the same as HDR10 but with the addition of a system of dynamic metadata developed by Samsung. It is free to use for content creators and has a maximum $ 10,000 annual license for some manufacturers. It has been positioned as an alternative to Dolby Vision without the same expenses. HLG format is an HDR format that can be used for video and still images. It uses

2781-525: Is an ITU-R Recommendation released in July 2016 that defines high dynamic range (HDR) formats for both HDTV 1080p and 4K/8K UHDTV resolutions. These formats use the same color primaries as Rec. 2020, but with different transfer functions for HDR use. Rec. 2100 does not support the YcCbcCrc scheme of Rec. 2020. High-dynamic-range television High-dynamic-range television ( HDR-TV )

2884-409: Is an attempt to make the differences in HDR specifications easier to understand for consumers, with standards mainly used in computer monitors and laptops. VESA defines a set of HDR levels; all of them must support HDR10, but not all are required to support 10-bit displays. DisplayHDR is not an HDR format, but a tool to verify HDR formats and their performance on a given monitor. The most recent standard

2987-516: Is an open HDR standard announced on 27 August 2015 by the Consumer Technology Association . It is the most widespread of the HDR formats, and is not backward compatible with SDR displays. It is technically limited to a maximum peak brightness of 10,000 nits; however, HDR10 content is commonly mastered with a peak brightness between 1000 and 4000 nits. HDR10 lacks dynamic metadata. On HDR10 displays that have lower color volume than

3090-987: Is below the visual modulation threshold, the ability to discern a one-value difference in luminance , for the entire luminance range. The NHK is planning for their UHDTV system, Super Hi-Vision , to use 12 bits per sample RGB . Rec. 2020 defines a nonlinear transfer function for gamma correction that is the same nonlinear transfer function that is used by Rec. 709 , except that its parameters are (for 12 bit only) given with higher precision: E ′ = { 4.5 E 0 ≤ E < β α E 0.45 − ( α − 1 ) β ≤ E ≤ 1 {\displaystyle E^{\prime }={\begin{cases}4.5E&0\leq E<\beta \,\!\\\alpha \,\!E^{0.45}-(\alpha \,\!-1)&\beta \,\!\leq E\leq 1\end{cases}}} The standard says that for practical purposes,

3193-492: Is commonly associated to a WCG (a system chromaticity wider than BT.709 ). Rec. 2100 (HDR-TV) uses the same system chromaticity that is used in Rec. 2020 (UHDTV). HDR formats such as HDR10, HDR10+, Dolby Vision and HLG also use Rec. 2020 chromaticities. HDR contents are commonly graded on a P3-D65 display. Because of the increased dynamic range , HDR contents need to use more bit depth than SDR to avoid banding. While SDR uses

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3296-439: Is completed. The top two bars of the test image help to set correct contrast and brightness values. There are eight three-digit numbers in each bar. A good monitor with proper calibration shows the six numbers on the right in both bars, a cheap monitor shows only four numbers. Given a desired display-system gamma, if the observer sees the same brightness in the checkered part and in the homogeneous part of every colored area, then

3399-400: Is mainly achieved by the use of PQ or HLG transfer function . WCGs are also commonly used along HDR up to Rec. 2020 color primaries . A bit depth of 10 or 12 bits is used to not see banding across the extended brightness range. In some cases, additional metadata are used to handle the variety in displays brightness , contrast and colors. HDR video is defined in Rec. 2100. Rec. 2100

3502-455: Is non-linear and better approximated by gamma. (Emulating "stepping back," which motivates downsampling in linear light (gamma=1), does not apply when upsampling.) A related method of reducing the visibility of ringing artifacts consists of using a sigmoidal light transfer function as pioneered by ImageMagick and GIMP 's LoHalo filter and adapted to video upsampling by madVR , AviSynth and Mpv . The term intensity refers strictly to

3605-471: Is sometimes applied to various measures, including light levels, though it more properly applies to a subjective visual attribute. Gamma correction is a type of power law function whose exponent is the Greek letter gamma ( γ ). It should not be confused with the mathematical Gamma function . The lower case gamma, γ , is a parameter of the former; the upper case letter, Γ, is the name of (and symbol used for)

3708-435: Is still based on and limited by the characteristics of older cathode-ray tubes (CRTs), despite the huge advances in screen and display technologies since CRT's obsolescence. SDR formats are able to represent a maximum luminance level of around 100 nits . For HDR, this number increases to around 1,000–10,000 nits. HDR can represent darker black levels and more saturated colors. The most common SDR formats are limited to

3811-428: Is the Greek letter gamma . For a CRT, the gamma that relates brightness to voltage is usually in the range 2.35 to 2.55; video look-up tables in computers usually adjust the system gamma to the range 1.8 to 2.2, which is in the region that makes a uniform encoding difference give approximately uniform perceptual brightness difference, as illustrated in the diagram at the top of this section. For simplicity, consider

3914-578: Is used in sjpeg and optionally in AVIF . Kornelski provides a simpler approximation by luma-based weighted average. Alpha compositing , color gradients , and 3D rendering are also affected by this issue. Paradoxically, when upsampling (scaling up) an image, the result processed in a "wrong" (non-physical) gamma color space is often more aesthetically pleasing. This is because resampling filters with negative lobes like Mitchell–Netravali and Lanczos create ringing artifacts linearly even though human perception

4017-476: Is useful for making a monitor display images approximately correctly, on systems in which profiles are not used (for example, the Firefox browser prior to version 3.0 and many others) or in systems that assume untagged source images are in the sRGB colorspace. In the test pattern, the intensity of each solid color bar is intended to be the average of the intensities in the surrounding striped dither; therefore, ideally,

4120-508: The Adobe RGB color space covers 52.1%, the DCI-P3 digital cinema color space covers 45.5%, and the Rec. 709 color space covers 35.9%. During the development of the Rec. 2020 color space it was decided that it would use real colors, instead of imaginary colors , so that it would be possible to show the Rec. 2020 color space on a display without the need for conversion circuitry. Since

4223-579: The DNxHD codec . On January 6, 2015, the MHL Consortium announced the release of the superMHL specification which will support 8K resolution at 120 fps, 48-bit video, the Rec. 2020 color space, high dynamic range support, a 32-pin reversible superMHL connector, and power charging of up to 40 watts. On January 7, 2015, Ateme added support for the Rec. 2020 color space to their TITAN File video platform. On March 18, 2015, Arri announced

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4326-647: The High Efficiency Video Coding standard. 4K Blu-ray Discs support both a higher color precision by increasing the color depth to 10 bits per color, and a greater color gamut by using the Rec. 2020 color space. The 4K Blu-ray specification allows for three disc sizes: 50 gb, 66 gb and 100 gb. Depending on the disc size and physical configuration, the data rate can reach up to 128 Mbit/s. The first Ultra HD Blu-ray titles were officially released from four studios on March 1, 2016. On November 6, 2014, Google added support for

4429-419: The Rec. 709 / sRGB gamut, while common HDR formats use Rec. 2100, which is a wide color gamut (WCG). In practice, HDR is not always used at its limits. HDR contents are often limited to a peak brightness of 1,000 or 4,000 nits and P3-D65 colors, even if they are stored in formats capable of more. Content creators can choose to what extent they make use of HDR capabilities. They can constrain themselves to

4532-478: The Rec. 709 (HDTV) color space. The RGB primaries used by Rec. 2020 are equivalent to monochromatic light sources on the CIE 1931 spectral locus . The wavelength of the Rec. 2020 primary colors is 630  nm for the red primary color, 532 nm for the green primary color, and 467 nm for the blue primary color. In coverage of the CIE 1931 color space , the Rec. 2020 color space covers 75.8%,

4635-504: The gamma function ), with greater sensitivity to relative differences between darker tones than between lighter tones, consistent with the Stevens power law for brightness perception. If images are not gamma-encoded, they allocate too many bits or too much bandwidth to highlights that humans cannot differentiate, and too few bits or too little bandwidth to shadow values that humans are sensitive to and would require more bits/bandwidth to maintain

4738-482: The HDR10 and HLG formats of Rec. 2100, which are supposed to start by 2017. At SID display week 2018, various companies showcased displays that are able to cover over 90% of the Rec. 2020 color space. JDI showcased an improvement of their 17.3" LCD 8k broadcast monitor that is powered by an RGB laser backlight system. This allows the display to reproduce 97% of the Rec. 2020 color space. Rec. 2100

4841-406: The HDR10 content (such as lower peak brightness capability), the HDR10 metadata provides information to help the display adjust to the video. The metadata is static and constant with respect to each individual video, and does not inform the display exactly how the content should be adjusted. The interaction between display capabilities, video metadata, and the ultimate output (i.e. the presentation of

4944-816: The HDR10 format without any metadata. It uses the perceptual quantizer (PQ) transfer function, Rec. 2020 color primaries and a bit depth of 10-bits. HDR Vivid is an HDR format developed by the China Ultra HD Video Alliance (CUVA) and released in March 2021. It uses dynamic metadata standardized in CUVA 005-2020. Yearly license (for manufacturer) 1,000 - 4,000 nits (common) 1,000 - 4,000 nits (common) 4,000 nits common TV sets with enhanced dynamic range and upscaling of existing SDR/LDR video/broadcast content with reverse tone mapping have been anticipated since early 2000s. In 2016, HDR conversion of SDR video

5047-495: The HLG transfer function, Rec. 2020 color primaries, and a bit depth of 10 bits. The format is backwards compatible with SDR UHDTV , but not with older SDR displays that do not implement the Rec. 2020 color standards. It does not use metadata and is royalty-free. PQ10 , sometimes referred to as the PQ format, is an HDR format that can be used for video and still images. It is the same as

5150-449: The Rec. 2020 color space to VP9 . On November 7, 2014, DivX developers announced that DivX265 version 1.4.21 had added support for the Main 10 profile of HEVC and the Rec. 2020 color space. On December 22, 2014, Avid Technology released an update for Media Composer that added support for 4K resolution, the Rec. 2020 color space, and a bit rate of up to 3,730 Mbit/s with

5253-463: The Rec. 2020 color space. At SID display week 2017, AUO displayed a 5" foldable 720p HD AMOLED display able to display 95% of the Rec. 2020 colorspace. Although 720p is not specified by Rec. 2020, the color space coverage is of note. The Ultra HD Forum guidelines for UHD Phase A include support for SDR formats with 10 bits of color bit depth based on both Rec. 709 and Rec. 2020 color gamuts and also both

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5356-453: The Rec. 2020 color space. On January 27, 2016, VESA announced that DisplayPort version 1.4 will support the Rec. 2020 color space. On April 17, 2016, Sony presented a 55 in (140 cm) 4K  OLED display with the support of Rec. 2020 color space. On April 18, 2016, the Ultra ;HD Forum announced industry guidelines for UHD Phase A which includes support for

5459-407: The Rec. 2020 color space. On May 22, 2014, Nanosys announced that using a quantum dot enhancement film (QDEF) a current LCD TV was modified so that it could cover 91% of the Rec. 2020 color space. Nanosys engineers believe that with improved LCD color filters it is possible to make a LCD that covers 97% of the Rec. 2020 color space. On September 4, 2014, Canon Inc. released

5562-468: The Rec. 2020 color space. HDMI 2.0 can transmit 12 bits per sample RGB at a resolution of 2160p and a frame rate of 24/25/30 fps or it can transmit 12 bits per sample 4:2:2/4:2:0 YCbCr at a resolution of 2160p and a frame rate of 50/60 fps. The Rec. 2020 color space is supported by H.264/MPEG-4 AVC and H.265/ High Efficiency Video Coding (HEVC). The Main 10 profile in HEVC

5665-572: The SXT line of Arri Alexa cameras which will support Apple ProRes recording at 4K resolution and the Rec. 2020 color space. On April 8, 2015, Canon Inc. announced the DP-V2410 4K display and EOS C300 Mark II camera with support for the Rec. 2020 color space. On May 26, 2015, the NHK announced a 4K LCD with a laser diode backlight that covers 98% of the Rec. 2020 color space. Using

5768-533: The System Preferences. Generally, operations on pixel values should be performed in "linear light" (gamma 1). Eric Brasseur discusses the issue at length and provides test images. They serve to point out a widespread problem: Many programs perform scaling in a color space with gamma, instead of a physically correct linear space. The test images are constructed so as to have a drastically different appearance when downsampled incorrectly. Jonas Berlin has created

5871-536: The Y′, B′, and R′ signals with equations that depend on the range of values of B′−Y′ and R′−Y′. Just like standard definition content that uses SMPTE C or NTSC 1953 , BT.2020 primaries should be color managed to primaries of display. That is different from changing YCbCr matrix. HD content is color managed to BT.709 primaries on linear values. BT.2020 and BT.2100 are usually color managed to P3-D65. The reference color bars for BT.2020 are ARIB STD-B66. HDMI 2.0 supports

5974-492: The actual desired image luminance. With this nonlinear relationship, equal steps in encoded luminance correspond roughly to subjectively equal steps in brightness. Ebner and Fairchild used an exponent of 0.43 to convert linear intensity into lightness (luma) for neutrals; the reciprocal, approximately 2.33 (quite close to the 2.2 figure cited for a typical display subsystem), was found to provide approximately optimal perceptual encoding of grays. The following illustration shows

6077-453: The amount of light that is emitted per unit of time and per unit of surface, in units of lux . Note, however, that in many fields of science this quantity is called luminous exitance , as opposed to luminous intensity , which is a different quantity. These distinctions, however, are largely irrelevant to gamma compression, which is applicable to any sort of normalized linear intensity-like scale. "Luminance" can mean several things even within

6180-411: The brightness of small areas without increasing the overall image's brightness, resulting in, for example, bright reflections from shiny objects, bright stars in a dark night scene, and bright and colorful light-emissive objects (e.g. fire, and sunset). The shadows or lowlights—the darkest parts of an image—can be darker and more detailed. The colorful parts of the image can be even more colorful if

6283-469: The chroma components in YCbCr are calculated as C′ B  = 0.5⋅(B′−Y′)/(1−K B ) = (B'−Y′)/1.8814 and C′ R  = 0.5⋅(R′−Y′)/(1−K R ) = (R′−Y′)/1.4746, and for digital representation the Y′, C′ B , and C′ R signals are scaled, offset by constants, and rounded to integers. The YcCbcCrc scheme is a "constant luminance" luma-chroma representation. YcCbcCrc may be used when

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6386-438: The content creator's intents are not ensured to be preserved on less capable displays. For optimal quality, standards require video to be created and viewed in a relatively dark environment. Dolby Vision IQ and HDR10+ Adaptive adjust the content according to the ambient light. Since 2014, multiple HDR formats have emerged including HDR10 , HDR10+ , Dolby Vision , and HLG. Some formats are royalty-free and others require

6489-440: The context of video and imaging: One contrasts relative luminance in the sense of color (no gamma compression) with luma in the sense of video (with gamma compression), and denote relative luminance by Y and luma by Y ′, the prime symbol (′) denoting gamma compression. Note that luma is not directly calculated from luminance, it is the (somewhat arbitrary) weighted sum of gamma compressed RGB components. Likewise, brightness

6592-421: The curve in any particular region. When a photographic film is exposed to light, the result of the exposure can be represented on a graph showing log of exposure on the horizontal axis, and density, or negative log of transmittance, on the vertical axis. For a given film formulation and processing method, this curve is its characteristic or Hurter–Driffield curve . Since both axes use logarithmic units,

6695-399: The difference between a scale with linearly-increasing encoded luminance signal (linear gamma-compressed luma input) and a scale with linearly-increasing intensity scale (linear luminance output). On most displays (those with gamma of about 2.2), one can observe that the linear-intensity scale has a large jump in perceived brightness between the intensity values 0.0 and 0.1, while the steps at

6798-472: The different elements; if done incorrectly, these conversions can lead to highly distorted results, but if done correctly as dictated by standards and conventions will lead to a properly functioning system. In a typical system, for example from camera through JPEG file to display, the role of gamma correction will involve several cooperating parts. The camera encodes its rendered image into the JPEG file using one of

6901-535: The dynamic range of images and videos from their capture and creation to their storage, distribution and display. Often, HDR is used with wide color gamut (WCG) technology. WCG increases the gamut and number of distinct colors available. HDR increases the range of luminance available for each color. HDR and WCG are separable but complementary technologies. Standards-compliant HDR display also has WCG capabilities, as mandated by Rec. 2100 and other common HDR specifications. The use of HDR in television sets began in

7004-413: The effect of ambient light on the CRT. In such expressions the exponent is not the gamma; for instance, the sRGB function uses a power of 2.4 in it, but more closely resembles a power-law function with an exponent of 2.2, without a linear portion. Up to four elements can be manipulated in order to achieve gamma encoding to correct the image to be shown on a typical 2.2- or 1.8-gamma computer display: In

7107-419: The example of a monochrome CRT. In this case, when a video signal of 0.5 (representing a mid-gray) is fed to the display, the intensity or brightness is about 0.22 (resulting in a mid-gray, about 22% the intensity of white). Pure black (0.0) and pure white (1.0) are the only shades that are unaffected by gamma. To compensate for this effect, the inverse transfer function (gamma correction) is sometimes applied to

7210-481: The expansive power-law nonlinearity is called gamma expansion . Gamma encoding of images is used to optimize the usage of bits when encoding an image, or bandwidth used to transport an image, by taking advantage of the non-linear manner in which humans perceive light and color. The human perception of brightness ( lightness ), under common illumination conditions (neither pitch black nor blindingly bright), follows an approximate power function (which has no relation to

7313-437: The following power-law expression: where the non-negative real input value V in {\displaystyle V_{\text{in}}} is raised to the power γ {\displaystyle \gamma } and multiplied by the constant A to get the output value V out {\displaystyle V_{\text{out}}} . In the common case of A = 1 , inputs and outputs are typically in

7416-729: The following values of α and β can be used: While the Rec. 2020 transfer function can be used for encoding, it is expected that most productions will use a reference monitor that has an appearance of using equivalent of gamma 2.4 transfer function as defined in ITU-R BT.1886 and that the reference monitor will be evaluated under viewing conditions as defined in Rec. ITU-R BT.2035. Rec. 2020 allows for RGB and luma-chroma signal formats with 4:4:4 full-resolution sampling and luma-chroma signal formats with 4:2:2 and 4:2:0 chroma subsampling . It supports two types of luma-chroma signals, called YCbCr and YcCbcCrc. YCbCr may be used when

7519-576: The full range of brightness and color of HDR formats. A display is called an HDR display if it can accept HDR content and map them to its display characteristics, so the HDR logo only provides information about content compatibility and not display capability. Displays that use global dimming, such as most edge-lit LED displays, cannot display the advanced contrast of HDR content. Some displays implement local dimming technologies, such as OLED and full-array LED-backlighting , to more properly display advanced contrast. The DisplayHDR standard from VESA

7622-720: The gAMA chunk for this purpose and with formats such as JPEG and TIFF the Exif Gamma tag can be used. Some formats can specify the ICC profile which includes a transfer function. These features have historically caused problems, especially on the web. For HTML and CSS colors and JPG or GIF images without attached color profile metadata, popular browsers passed numerical color values to the display without color management, resulting in substantially different appearance between devices; however those same browsers sent images with gamma explicitly set in metadata through color management, and also applied

7725-444: The gamma characteristics of the display device. The similarity of CRT physics to the inverse of gamma encoding needed for video transmission was a combination of coincidence and engineering, which simplified the electronics in early television sets. Photographic film has a much greater ability to record fine differences in shade than can be reproduced on photographic paper . Similarly, most video screens are not capable of displaying

7828-531: The gamma correction is approximately correct. In many cases the gamma correction values for the primary colors are slightly different. Setting the color temperature or white point is the next step in monitor adjustment. Before gamma correction the desired gamma and color temperature should be set using the monitor controls. Using the controls for gamma, contrast and brightness, the gamma correction on an LCD can only be done for one specific vertical viewing angle, which implies one specific horizontal line on

7931-400: The gamma expansion of the CRT (although it is not the exact inverse). For television signals, gamma values are fixed and defined by the analog video standards. CCIR System M and N , associated with NTSC color, use gamma 2.2; systems B / G , H , I , D / K , K1 , L and M associated with PAL or SECAM color use gamma 2.8. In most computer display systems, images are encoded with

8034-448: The gamma slider in the dccw program until the last colored area, often the green color, has the same brightness in checkered and homogeneous area. Use the color balance or individual colors gamma correction sliders in the gamma correction programs to adjust the two other colors. Some old graphics card drivers do not load the color Look Up Table correctly after waking up from standby or hibernate mode and show wrong gamma. In this case update

8137-415: The graphics card driver. On some operating systems running the X Window System , one can set the gamma correction factor (applied to the existing gamma value) by issuing the command xgamma -gamma 0.9 for setting gamma correction factor to 0.9, and xgamma for querying current value of that factor (the default is 1.0). In macOS systems, the gamma and other related screen calibrations are made through

8240-448: The higher end of the scale are hardly perceptible. The gamma-encoded scale, which has a nonlinearly-increasing intensity, will show much more even steps in perceived brightness. A CRT, for example, converts a video signal to light in a nonlinear way, because the electron gun's intensity (brightness) as a function of applied video voltage is nonlinear. The light intensity I is related to the source voltage V s according to where γ

8343-408: The intended reproduction is almost always nonlinearly related to the measured scene intensities, via a tone reproduction nonlinearity. The concept of gamma can be applied to any nonlinear relationship. For the power-law relationship V out = V in γ {\displaystyle V_{\text{out}}=V_{\text{in}}^{\gamma }} , the curve on a log–log plot

8446-449: The late 2010s. By 2020, most high-end and mid-range TVs supported HDR, and some budget models did as well. HDR-TVs are now the standard for most new televisions. There are a number of different HDR formats, including HDR10 , HDR10+ , Dolby Vision , and HLG . HDR10 is the most common format, and is supported by all HDR-TVs. Dolby Vision is a more advanced format that offers some additional features, such as scene-by-scene mastering. HDR10+

8549-427: The latter (as in Γ( x )). To use the word "function" in conjunction with gamma correction, one may avoid confusion by saying "generalized power law function". Without context, a value labeled gamma might be either the encoding or the decoding value. Caution must be taken to correctly interpret the value as that to be applied-to-compensate or to be compensated-by-applying its inverse. In common parlance, in many occasions

8652-409: The light intensity varies nonlinearly with the electron-gun voltage. Altering the input signal by gamma compression can cancel this nonlinearity, such that the output picture has the intended luminance. However, the gamma characteristics of the display device do not play a factor in the gamma encoding of images and video. They need gamma encoding to maximize the visual quality of the signal, regardless of

8755-422: The limits of SDR even if the content is delivered in an HDR format. The benefits of HDR depend on the display capabilities, which vary. No current display is able to reproduce the maximal range of brightness and colors that can be represented in HDR formats. The highlights—the brightest parts of an image—can be brighter, more colorful, and more detailed. The larger capacity for brightness can be used to increase

8858-563: The monitor, at one specific brightness and contrast level. An ICC profile allows one to adjust the monitor for several brightness levels. The quality (and price) of the monitor determines how much deviation of this operating point still gives a satisfactory gamma correction. Twisted nematic (TN) displays with 6-bit color depth per primary color have lowest quality. In-plane switching (IPS) displays with typically 8-bit color depth are better. Good monitors have 10-bit color depth, have hardware color management and allow hardware calibration with

8961-466: The nominal peak. 12 bits per sample Rec. 2020 uses video levels where the black level is defined as code 256 and the nominal peak is defined as code 3760. Codes 0–15 and 4,080–4,095 are used for the timing reference. Codes 16 through 255 provide video data below the black level while codes 3,761 through 4,079 provide video data above the nominal peak. The Rec. 2020 (UHDTV/UHD-1/UHD-2) color space can reproduce colors that cannot be shown with

9064-407: The process of rendering linear raw data to conventional RGB data (e.g. for storage into JPEG image format), color space transformations and rendering transformations will be performed. In particular, almost all standard RGB color spaces and file formats use a non-linear encoding (a gamma compression) of the intended intensities of the primary colors of the photographic reproduction. In addition,

9167-410: The range 0–1. A gamma value γ < 1 {\displaystyle \gamma <1} is sometimes called an encoding gamma , and the process of encoding with this compressive power-law nonlinearity is called gamma compression ; conversely, a gamma value γ > 1 {\displaystyle \gamma >1} is called a decoding gamma , and the application of

9270-454: The range of brightnesses (dynamic range) that can be captured by typical electronic cameras. For this reason, considerable artistic effort is invested in choosing the reduced form in which the original image should be presented. The gamma correction, or contrast selection, is part of the photographic repertoire used to adjust the reproduced image. Analogously, digital cameras record light using electronic sensors that usually respond linearly. In

9373-562: The red curve is a standard γ = 2.2 power-law curve, for comparison. Gamma correction in computers is used, for example, to display a gamma = 1.8 Apple picture correctly on a gamma = 2.2 PC monitor by changing the image gamma. Another usage is equalizing of the individual color-channel gammas to correct for monitor discrepancies. Some picture formats allow an image's intended gamma (of transformations between encoded image samples and light output) to be stored as metadata , facilitating automatic gamma correction. The PNG specification includes

9476-442: The same visual quality. Gamma encoding of floating-point images is not required (and may be counterproductive), because the floating-point format already provides a piecewise linear approximation of a logarithmic curve. Although gamma encoding was developed originally to compensate for the brightness characteristics of cathode-ray tube (CRT) displays, that is not its main purpose or advantage in modern systems. In CRT displays,

9579-448: The slope of the linear section of the curve is called the gamma of the film. Negative film typically has a gamma less than 1; positive film (slide film, reversal film) typically has a gamma with absolute value greater than 1. Output to CRT-based television receivers and monitors does not usually require further gamma correction. The standard video signals that are transmitted or stored in image files incorporate gamma compression matching

9682-399: The solid areas and the dithers should appear equally bright in a system properly adjusted to the indicated gamma. Normally a graphics card has contrast and brightness control and a transmissive LCD monitor has contrast, brightness, and backlight control. Graphics card and monitor contrast and brightness have an influence on effective gamma, and should not be changed after gamma correction

9785-529: The standard gamma values such as 2.2, for storage and transmission. The display computer may use a color management engine to convert to a different color space (such as older Macintosh's γ = 1.8 color space) before putting pixel values into its video memory. The monitor may do its own gamma correction to match the CRT gamma to that used by the video system. Coordinating the components via standard interfaces with default standard gamma values makes it possible to get such system properly configured. This procedure

9888-451: The top priority is compatibility with existing SDTV and HDTV operating practices. The luma (Y′) signal for YCbCr is calculated as the weighted average Y′ = K R ⋅R′ + K G ⋅G′ + K B ⋅B′, using the gamma-corrected RGB values (denoted R′G′B′) and the weighting coefficients K R  = 0.2627, K G  = 1−K R −K B  = 0.678, and K B  = 0.0593. As in similar schemes ,

9991-434: The top priority is the most accurate retention of luminance information. The luma component in YcCbcCrc is calculated using the same coefficient values as for YCbCr, but it is calculated from linear RGB and then gamma corrected, rather than being calculated from gamma-corrected R′G′B′ and is done as follows: Y′ = (K R ⋅R + K G ⋅G + K B ⋅B)′. The chroma components in YcCbcCrc are calculated from

10094-460: The traditional gamma curve. If the gamma curve would have been extended to 10,000 nits, it would have required a bit-depth of 15 bits to avoid banding. HDR transfer functions: SDR for HD video uses a system chromaticity ( chromaticity of color primaries and white point ) specified in Rec. 709 (same as sRGB ). SDR for SD used many different primaries, as said in BT.601, SMPTE 170M and BT.470. HDR

10197-420: The video signal so that the end-to-end response is linear. In other words, the transmitted signal is deliberately distorted so that, after it has been distorted again by the display device, the viewer sees the correct brightness. The inverse of the function above is where V c is the corrected voltage, and V s is the source voltage, for example, from an image sensor that converts photocharge linearly to

10300-476: The video) is mediated by the display, with the result that the original producer's intent may not be preserved. Dolby Vision is an end-to-end ecosystem for HDR video, and covers content creation, distribution, and playback. It uses dynamic metadata and is capable of representing luminance levels of up to 10,000 nits. Dolby Vision certification requires displays for content creators to have a peak luminance of at least 1,000 nits. HDR10+, also known as HDR10 Plus,

10403-459: Was added based on proposal JCTVC-K0109 which proposed that a 10-bit profile be added to HEVC for consumer applications. The proposal stated that this was to allow for improved video quality and to support the Rec. 2020 color space that will be used by UHDTV. On September 11, 2013, ViXS Systems announced the XCode 6400 SoC which supports 4K resolution at 60 fps, the Main 10 profile of HEVC, and

10506-501: Was released in April 2015 and DisplayPort 1.4, which was released in March 2016. On 12 December 2016, HDMI announced that HLG support had been added to the HDMI 2.0b standard. HDMI 2.1 was officially announced on 4 January 2017, and added support for Dynamic HDR, which is dynamic metadata that supports changes scene-by-scene or frame-by-frame. As of 2020, no display is capable of rendering

10609-472: Was released to market as Samsung 's HDR+ (in LCD TV sets) and Technicolor SA's HDR Intelligent Tone Management. As of 2018, high-end consumer-grade HDR displays can achieve 1,000 cd/m of luminance, at least for a short duration or over a small portion of the screen, compared to 250-300 cd/m for a typical SDR display. Video interfaces that support at least one HDR Format include HDMI 2.0a, which

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