High dynamic range

High dynamic range (HDR), also known as wide dynamic range, extended dynamic range, or expanded dynamic range, is a dynamic range higher than usual.

The term is often used in discussing the dynamic range of various signals such as images, videos, audio or radio. It may apply to the means of recording, processing, and reproducing such signals including analog and digitized signals.<ref>Robertson, Mark A.; Borman, Sean; Stevenson, Robert L. (April 2003). "Estimation-theoretic approach to dynamic range enhancement using multiple exposures". Journal of Electronic Imaging. 12 (2): 220, right column, line 26219–228. Bibcode:2003JEI....12..219R. doi:10.1117/1.1557695. The first report of digitally combining multiple pictures of the same scene to improve dynamic range appears to be Mann</ref>

The term is also the name of some of the technologies or techniques allowing to achieve high dynamic range images, videos, or audio.

Imaging

In this context, the term high dynamic range means there is a lot of variation in light levels within a scene or an image. The dynamic range refers to the range of luminosity 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.<ref>Dufaux, Frédéric; Le Callet, Patrick; Mantiuk, Rafal; Mrak, Marta (2016). High Dynamic Range Video – From Acquisition to Display and Applications. Elsevier. doi:10.1016/C2014-0-03232-7. ISBN 978-0-08-100412-8.</ref>

Modern movies have often been filmed with cameras featuring a higher dynamic range, and legacy movies can be converted even if manual intervention would be needed for some frames (as when black-and-white films are converted to color). Also, special effects, especially those that mix real and synthetic footage, require both HDR shooting and rendering. 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, in surveillance video systems, and other applications.

Capture

Main article: Multi-exposure HDR capture

In photography and videography, a technique, commonly named high dynamic range (HDR), allows to increase the dynamic range of captured photos and videos beyond the native capability of the camera. It consists of capturing multiple frames of the same scene but with different exposures and then combining them into one, resulting into an image with a dynamic range higher than those of individually captured frames.<ref name="mann1993">"Compositing Multiple Pictures of the Same Scene", by Steve Mann, in IS&T's 46th Annual Conference, Cambridge, Massachusetts, May 9–14, 1993</ref><ref name=":0">Reinhard, Erik; Ward, Greg; Pattanaik, Sumanta; Debevec, Paul (2005). High dynamic range imaging: acquisition, display, and image-based lighting. Amsterdam: Elsevier/Morgan Kaufmann. p. 7. ISBN 978-0-12-585263-0. 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.</ref>

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.

Modern CMOS image sensors can often capture a high dynamic range images from a single exposure.<ref name=":1">Arnaud Darmont (2012). High Dynamic Range Imaging: Sensors and Architectures (First ed.). SPIE press. ISBN 978-0-81948-830-5.</ref> This reduces the need to use the multi-exposure HDR capture technique.

High dynamic range captured 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".

Because of the nonlinearity of some sensors image artifacts can be common.

Rendering

Main article: High-dynamic-range rendering

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).<ref name="6800_Leagues_HDR">Simon Green and Cem Cebenoyan (2004). "High Dynamic Range Rendering (on the GeForce 6800)" (PDF). GeForce 6 Series. nVidia. p. 3.</ref>

Dynamic range compression or expansion

Main article: Tone mapping

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 be tone mapped in order to reduce that dynamic range.

Storage

High-dynamic-range formats for image and video files are able to store more dynamic range than traditional 8-bit gamma formats. These formats include:

• Formats that are only used for storage purpose, such as:
  • Raw image formats
  • Formats that use a linear transfer function with high bit-depth
  • Formats that use a logarithmic transfer function
  • OpenEXR
  • ACES
• HDR formats that can be used for both storage and transmission to displays, such as:
  • HDR10
  • HDR10+
  • Dolby Vision
  • HLG
  • ISO/AWI 21496 Gain map, a layer built on top of SDR formats<ref>Chan, Eric (Adobe); Hubel, Paul M. (Apple) (January 2023). Embedded Gain Maps for Adaptive Display of High Dynamic Range Images. Stereoscopic Displays and Applications XXXIV.</ref> – formerly Apple EDR<ref>"Apple's "EDR" Brings High Dynamic Range to Non-HDR Displays". Prolost. 4 December 2020.</ref>
  • Ultra HDR, a gain map image in a JPEG image file, and backwards compatible with SDR displays<ref>"Ultra HDR Image Format v1.0". Android Developers. Retrieved 2023-12-19.</ref>

OpenEXR was created in 1999 by Industrial Light & Magic (ILM) and released in 2003 as an open source software library.<ref>"Industrial Light & Magic Releases Proprietary Extended Dynamic Range Image File Format OpenEXR to Open Source Community" (PDF) (Press release). 22 January 2003. Archived from the original (PDF) on 21 July 2017. Retrieved 27 July 2016.</ref><ref name="OpenEXRdotCom">"Main OpenEXR web site". Archived from the original on 16 January 2013. Retrieved 27 July 2016.</ref> OpenEXR is used for film and television production.<ref name="OpenEXRdotCom" />

Academy Color Encoding System (ACES) was created by the Academy of Motion Picture Arts and Sciences and released in December 2014.<ref name="ACESOverviewDecember2014ACES">"ACES". Academy of Motion Picture Arts and Sciences. Archived from the original on 1 August 2016. Retrieved 29 July 2016.</ref> ACES is a complete color and file management system that works with almost any professional workflow and it supports both HDR and wide color gamut.<ref name="ACESOverviewDecember2014ACES" />

Transmission to displays

Main article: High-dynamic-range video

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 as color gamut.

In this context,

• HDR displays refers to displays compatible with that technology.
• HDR formats refers to formats such as HDR10, HDR10+, Dolby Vision and HLG.
• HDR video refers to a video encoded in an HDR format. Thoses HDR video have a greater bit depth, luminance and color volume than standard dynamic range (SDR) video which uses a conventional gamma curve.<ref name="DisplayHDR2015BBC">T. Borer; A. Cotton. "A "Display Independent" High Dynamic Range Television System" (PDF). BBC. Retrieved 2015-11-01.</ref>

On January 4, 2016, the Ultra HD Alliance announced their certification requirements for an HDR display.<ref name="UltraHDRJanuary2016BusinessWire">"UHD Alliance Defines Premium Home Entertainment Experience". Business Wire. 2016-01-04. Retrieved 2016-07-24.</ref><ref name="UltraHDRJanuary2016CNet">"What is UHD Alliance Premium Certified?". CNET. 2016-03-11. Retrieved 2016-07-24.</ref> The HDR display must have either a peak brightness of over 1000 cd/m² and a black level less than 0.05 cd/m² (a contrast 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).<ref name="UltraHDRJanuary2016BusinessWire" /><ref name="UltraHDRJanuary2016CNet" /> The two options allow for different types of HDR displays such as LCD and OLED.<ref name="UltraHDRJanuary2016CNet" />

Some options to use HDR transfer functions that better match the human visual system other than a conventional gamma curve include the HLG and perceptual quantizer (PQ).<ref name="DisplayHDR2015BBC" /><ref name="HPATechFebruary2014">Adam Wilt (2014-02-20). "HPA Tech Retreat 2014 – Day 4". DV Info Net. Retrieved 2014-11-05.</ref><ref name="GradingHDR2015studiodaily">Bryant Frazer (2015-06-09). "Colorist Stephen Nakamura on Grading Tomorrowland in HDR". studiodaily. Retrieved 2015-09-21.</ref> HLG and PQ require a bit depth of 10-bits per sample.<ref name="DisplayHDR2015BBC" /><ref name="HPATechFebruary2014" />

Display

See also: History of display technology, Backlight § Backlight dimming, OLED, and High-dynamic-range television

The dynamic range of a display refers to range of luminosity the display can reproduce, from the black level to its peak brightness. The contrast of a display refers to the ratio between the luminance of the brightest white and the darkest black that a monitor can produce.<ref>"Our Monitor Picture Quality Tests: Contrast". RTINGS.com. Retrieved 2021-12-29.</ref> 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 the Society 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.<ref>Seetzen, Helge; Whitehead, Lorne A.; Ward, Greg (2003). "54.2: A High Dynamic Range Display Using Low and High Resolution Modulators". SID Symposium Digest of Technical Papers. 34 (1): 1450–1453. doi:10.1889/1.1832558. ISSN 2168-0159. S2CID 15359222.</ref> In April 2007, BrightSide Technologies was acquired by Dolby Laboratories.<ref>"Dolby Laboratories (DLB) Acquires BrightSide for $28M". StreetInsider.com. Retrieved 2021-08-17..</ref>

OLED displays have high contrast. MiniLED improves contrast.

Realtime HDR vision

Mann's HDR (high-dynamic-range) welding helmet augments the image in dark areas and diminishes it in bright areas, thus implementing computer-mediated reality.

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.<ref>Quantigraphic camera promises HDR eyesight from Father of AR, by Chris Davies, SlashGear, Sep 12th 2012</ref><ref name=IEEE-Spectrum>Ackerman, Elise (31 Dec 2012). "Why Smart Glasses Might Not Make You Smarter". IEEE Spectrum. Retrieved 1 Jan 2017.</ref><ref>Mann, Steve (February 1997). "Wearable Computing: A First Step Toward Personal Imaging". IEEE Computer. 30 (2): 25–32. doi:10.1109/2.566147. S2CID 28001657.</ref><ref>"A magical welding helmet that lets you see the world in HDR–in real-time". Archived from the original on 2016-03-28. Retrieved 2018-03-24.</ref><ref>Mann, Steve (Fall 2012). "Through the Glass, Lightly". IEEE Technology and Society Magazine. 31 (3): 10–14. doi:10.1109/MTS.2012.2216592.</ref><ref>"'GlassEyes': The Theory of EyeTap Digital Eye Glass, supplemental material for 'Through the Glass, Lightly'" (PDF). IEEE Technology and Society Magazine. 31 (3). Fall 2012.</ref>

Non-imaging

Audio

In Audio, the term high dynamic range means there is a lot of variation in the levels of the sound. Here, the dynamic 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 in EA Digital Illusions CE Frostbite Engine to allow relatively louder sounds to drown out softer sounds.<ref name=FrostbiteEngineTrailer>EA DICE/Electronic Arts (2007). "Battlefield: Bad Company - Frostbite Engine Trailer" (video). Electronic Arts. Archived from the original on 2021-12-22.</ref>

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.

Radio

In radio, high dynamic range is important especially when there are potentially interfering signals. Measures such as spurious-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 and software-defined radio design.

Instrumentation

In many fields, instruments need to have a very high dynamic range. For example, in seismology, HDR accelerometers are needed, as in the ICEARRAY instruments.

See also

• Rec. 2100 – ITU-R Recommendation for HDR
• Ultra HD Forum – Organization that has created standards for HDR
• Color space
• Color grading

External links

• "High Dynamic Range (HDR) on Intel Graphics" (PDF). Intel Corporation. November 2017.