High dynamic range (HDR), also known aswide dynamic range,extended dynamic range, orexpanded dynamic range, is asignal with a higherdynamic range than usual.
The term is often used in discussing the dynamic ranges ofimages,videos,audio orradio. It may also apply to the means of recording, processing, and reproducing such signals includinganalog anddigitized signals.[1]
In this context, the termhigh dynamic range means there is a large amount of variation in light levels within a scene or an image. Thedynamic range refers to the range ofluminosity between the brightest area and the darkest area of that scene or image.
High dynamic range imaging (HDRI) refers to the set of imaging technologies and techniques that allow the dynamic range of images or videos to be increased. It covers the acquisition, creation, storage, distribution and display of images and videos.[2]
Modern films have often been shot with cameras featuring a higher dynamic range, and legacy films can be post-converted even if manual intervention will be needed for some frames (as when black-and-white films are converted to color).[citation needed] Also, special effects, especially those that mix real and synthetic footage, require both HDR shooting andrendering.[citation needed] HDR video is also needed in applications that demand high accuracy for capturing temporal aspects of changes in the scene. This is important in monitoring of some industrial processes such as welding, in predictive driver assistance systems in automotive industry, insurveillance video systems, and other applications.
Inphotography andvideography, a technique, commonly namedhigh dynamic range (HDR) allows the dynamic range of photos and videos to be captured beyond the native capability of the camera. It consists of capturing multiple frames of the same scene but with differentexposures and then combining them into one, resulting into an image with a dynamic range higher than the individually captured frames.[3][4]
Some of the sensors on modern phones and cameras may even combine the two images on-chip. This also allows a wider dynamic range being directly available to the user for display or processing without in-pixel compression. Some cameras designed for use in security applications can capture HDR videos by automatically providing two or more images for each frame, with changing exposure. For example, a sensor for 30fps video will give out 60fps with the odd frames at a short exposure time and the even frames at a longer exposure time.[citation needed]
ModernCMOSimage sensors can often capture high dynamic range images from a single exposure.[5] This reduces the need to use the multi-exposure HDR capture technique.
High dynamic range images are used in extreme dynamic range applications like welding or automotive work. In security cameras the term used instead of HDR is "wide dynamic range".[citation needed]
Because of the nonlinearity of some sensors image artifacts can be common.[citation needed]
High-dynamic-range rendering (HDRR) is the real-time rendering and display of virtual environments using a dynamic range of 65,535:1 or higher (used in computer, gaming, and entertainment technology).[6] HDRR does not require aHDR display and originally usedtone mapping to display the rendering on astandard dynamic range display.
The technologies used to store, transmit, display and print images have limited dynamic range. When captured or created images have a higher dynamic range, they must betone mapped in order to reduce that dynamic range.[citation needed]
High-dynamic-range formats for image and video files are able to store more dynamic range than traditional 8-bitgamma formats. These formats include:
High dynamic range (HDR) is also the common name of a technology allowing to transmit high dynamic range videos and images to compatible displays. That technology also improves other aspects of transmitted images, such ascolor gamut.
In this context,
On January 4, 2016, the Ultra HD Alliance announced their certification requirements for an HDR display.[23][24] The HDR display must have either a peak brightness of over 1000cd/m2 and a black level less than 0.05 cd/m2 (acontrast ratio of at least 20,000:1) or a peak brightness of over 540 cd/m2 and a black level less than 0.0005 cd/m2 (a contrast ratio of at least 1,080,000:1).[23][24] The two options allow for different types of HDR displays such asLCD andOLED.[24]
Some options to use HDRtransfer functions that better match the humanvisual system other than a conventional gamma curve include the HLG andperceptual quantizer (PQ).[22][25][26] HLG and PQ require abit depth of 10-bits per sample.[22][25]
The dynamic range of a display refers to range ofluminosity the display can reproduce, from the black level to its peak brightness.[citation needed] Thecontrast of a display refers to theratio between the luminance of the brightest white and the darkest black that a monitor can produce.[27] Multiple technologies allowed to increase the dynamic range of displays.
In May 2003,BrightSide Technologies demonstrated the first HDR display at the Display Week Symposium of theSociety for Information Display. The display used an array of individually-controlled LEDs behind a conventional LCD panel in a configuration known as "local dimming". BrightSide later introduced a variety of related display and video technologies enabling visualization of HDR content.[28] In April 2007,BrightSide Technologies was acquired byDolby Laboratories.[29]
OLED displays have high contrast.MiniLED improves contrast.[citation needed]
In the 1970s and 1980s,Steve Mann invented the Generation-1 and Generation-2 "Digital Eye Glass" as a vision aid to help people see better with some versions being built into welding helmets for HDR vision.[30][31][32][33][34][35]
In Audio, the termhigh dynamic range means there is a lot of variation in the levels of the sound. Here, thedynamic range refers to the range between the highest volume and lowest volume of the sound.
XDR (audio) is used to provide higher-quality audio when using microphone sound systems or recording onto cassette tapes.
HDR Audio is a dynamic mixing technique used inEA Digital Illusions CEFrostbite Engine to allow relatively louder sounds to drown out softer sounds.[36]
Dynamic range compression is a set of techniques used in audio recording and communication to put high-dynamic-range material through channels or media of lower dynamic range. Optionally,dynamic range expansion is used to restore the original high dynamic range on playback.
In radio, high dynamic range is important especially when there are potentially interfering signals. Measures such asspurious-free dynamic range are used to quantify the dynamic range of various system components such as frequency synthesizers. HDR concepts are important in both conventional andsoftware-defined radio design.
In many fields, instruments need to have a very high dynamic range. For example, inseismology, HDR accelerometers are needed, as in theICEARRAY instruments.
The first report of digitally combining multiple pictures of the same scene to improve dynamic range appears to be Mann
Images that store a depiction of the scene in a range of intensities commensurate with the scene are what we call HDR, or "radiance maps". On the other hand, we call images suitable for display with current display technology LDR.