High dynamic range
High dynamic range (HDR) is a dynamic range higher than what is considered to be standard dynamic range. The term is often used in discussing display devices, photography, 3D rendering, and sound recording including digital imaging and digital audio production. The term may apply to an analog or digitized signal, or to the means of recording, processing, and reproducing such signals.
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).
On January 4, 2016, the Ultra HD Alliance announced their certification requirements for a HDR display. 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). The two options allow for different types of HDR displays such as LCD and OLED.
Some options to use HDR transfer functions that better match the human visual system other than a conventional gamma curve include the Hybrid Log-Gamma (HLG) and Perceptual Quantizer (PQ). HLG and PQ require a bit depth of 10-bits per sample.
XDR (audio) is used to provide higher-quality audio when using microphone sound systems or recording onto cassette tapes.
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 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.
Realtime HDR visionEdit
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  See also, IEEE Technology and Society Magazine 31(3) and the supplemental material entitled "GlassEyes". 
- 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. 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
- "Compositing Multiple Pictures of the Same Scene", by Steve Mann, in IS&T's 46th Annual Conference, Cambridge, Massachusetts, May 9–14, 1993
- 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.
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- Mann, Steve (Fall 2012). "Through the Glass, Lightly". IEEE Technology and Society Magazine. 31 (3): 10–14. doi:10.1109/MTS.2012.2216592.
- "'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.
- "High Dynamic Range (HDR) on Intel Graphics" (PDF). Intel Corporation. November 2017.