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| PQ (electro‑optical transfer function) | |
|---|---|
| Name | PQ (electro‑optical transfer function) |
| Introduced | 2014 |
| Author | Dolby Laboratories |
| Standard | SMPTE ST 2084 |
| Domain | Imaging, Display technology, High Dynamic Range |
PQ (electro‑optical transfer function)
PQ (electro‑optical transfer function) is an electro‑optical transfer function developed for high dynamic range imaging and display systems. It maps encoded signal values to display luminance using a perceptually motivated nonlinear curve designed to match human visual sensitivity and to support wide color gamut and extended luminance ranges. The function was specified to enable consistent mastering, distribution, and display of HDR content across professional and consumer ecosystems.
PQ was specified by Dolby Laboratories and standardized in SMPTE ST 2084 to provide a perceptual curve for HDR mastering used in workflows associated with High Dynamic Range television, Digital Cinema, Ultra HD Blu-ray, and streaming services such as Netflix, Amazon Prime Video and Apple TV+. The transfer function is employed alongside color spaces and container formats defined by organizations like International Telecommunication Union and EBU, and it interacts with metadata frameworks from CTA and ISO. PQ is used in production chains including hardware from manufacturers such as Sony Corporation, Samsung Electronics, LG Electronics, Panasonic Corporation, and in post‑production tools from Avid Technology, Blackmagic Design, and Adobe Systems. Broad adoption by broadcasters and platforms such as BBC, NHK, Hulu, and YouTube has driven interoperability efforts among standards bodies including ITU-R, SMPTE, and ISO/IEC.
Technically, PQ is an electro‑optical transfer function that defines the relationship between an electrical signal level and resulting luminance output for displays and mastering monitors. It differs from earlier curves used by entities like Rec. 709 and ITU-R BT.2020 by focusing on perceptual uniformity across a much larger luminance span. The definition was formalized in SMPTE documents and implemented in device profiles influenced by work at Dolby Laboratories and validation studies by institutions such as Fraunhofer Society and Nokia. PQ supports metadata paradigms like SMPTE ST 2094 and dynamic metadata approaches compatible with manufacturers including Technicolor and Philips (company).
PQ's mathematical form is a static, parametric nonlinear mapping derived from models of human vision research including psychophysical experiments by teams associated with Stanford University, Massachusetts Institute of Technology, and Rochester Institute of Technology. The formal expression in SMPTE ST 2084 uses constants and rational exponents to map a normalized signal value to absolute luminance in cd/m², enabling targets up to 10,000 cd/m². The curve is expressed using parameters similar to modeling approaches in publications from Johnston et al. and work cited by Dolby Laboratories. Implementations rely on fixed‑point or floating‑point arithmetic optimized for platforms from Intel Corporation, AMD, ARM Holdings and GPUs from NVIDIA and AMD (company).
Implementations of PQ are found in professional mastering suites from Dolby Laboratories and in display firmware by Samsung Display, LG Display, and Sharp Corporation. PQ is used in signal chains compatible with transport formats such as MPEG‑TS, ISOBMFF, and delivery systems used by HBO, Disney+, and Sky (United Kingdom). In camera and capture workflows, manufacturers like RED Digital Cinema, ARRI, and Blackmagic Design provide LUTs and output options that interface with PQ‑based grading in tools from Blackmagic Design and Avid Technology. Display mapping often combines PQ with tone mapping algorithms developed by research groups at MIT Media Lab and University of California, Berkeley to adapt content to consumer panels by Samsung Electronics and Sony Corporation.
Performance characterization of PQ includes measurements of perceptual uniformity, peak luminance handling, quantization efficiency, and compatibility with metadata‑driven tone mapping. Metrics used by laboratories like NIST, Fraunhofer IIS, and CEA include just noticeable difference (JND) analyses, bit‑depth allocation efficiency, electrical to optical response linearity, and colorimetric stability across luminance ranges. Evaluations compare PQ performance on displays from LG Electronics, Sony Corporation, and Samsung Electronics using test patterns standardized by SMPTE and test labs such as UL.
PQ is frequently contrasted with alternatives including the perceptual approaches behind Hybrid Log‑Gamma (HLG) standardized by ITU‑R and joint efforts from BBC and NHK, as well as legacy EOTFs like those in Rec. 709 and SMPTE ST 274. Unlike HLG, PQ is absolute‑luminance oriented, which supports mastering for fixed peak luminance targets used by studios such as Warner Bros., Universal Pictures, and Paramount Pictures. Industry adoption choices often involve streaming platforms like Netflix and broadcasters like BT Group and DirecTV, which weigh PQ's deterministic mapping against HLG's backward‑compatible approach.
PQ's standardization via Society of Motion Picture and Television Engineers (SMPTE) as SMPTE ST 2084 and its inclusion in ecosystem profiles such as ULTRA HD Forum recommendations, CTA‑861.3, and ISO/IEC JTC 1 outputs has driven wide industry adoption. Major standards organizations including IEEE, IETF, and EBU have referenced PQ in technical reports and interoperability guidelines, and certification programs by entities like Dolby Laboratories and CTA verify implementations in consumer electronics certified by manufacturers including Samsung Electronics, Sony Corporation, LG Electronics, and Amazon.com devices.
Category:Imaging standards