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.
HDR transfer functions that better match the human visual system 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.
- "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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