A 2014 standard fixed how bright HDR mastering could go

The image

The document is SMPTE ST 2084:2014, titled High Dynamic Range Electro-Optical Transfer Function of Mastering Reference Displays, approved by the Society of Motion Picture and Television Engineers on 16 August 2014 and later reaffirmed in 2017. It is a fifteen-page engineering standard, not an image: definitions, an equation, and normative requirements for a mastering display's transfer function. The related ITU-R Recommendation BT.2100, approved in 2016, sits alongside it as a broadcast-oriented document referencing the same class of transfer function.

What the documents show

ST 2084's introduction states its scope directly: an electro-optical transfer function with a high luminance range capability of 0 to 10,000 candelas per square metre, intended, in the standard's own words, to enable the creation of video images with an increased luminance range, not for creation of video images with overall higher luminance levels. The standard is explicit that it does not impart a preferred rendering appearance for any particular viewing environment; image decisions remain the mastering colorist's. BT.2100 documents a separate, later-formalized alternative for the same underlying problem: it specifies both the Perceptual Quantization method that ST 2084 defines and a second, independently defined Hybrid Log-Gamma method, without presenting them as interchangeable; both documents share the same 10,000 candela reference value in their PQ equations, a detail visible by comparing the two texts directly rather than asserted by either alone.

Production context

The following extends past the documents themselves. A transfer function able to encode luminance up to 10,000 candelas per square metre exists so that mastering decisions, how bright a highlight can go before clipping, are separated from how any individual consumer display will eventually render that signal, a distinct, later mapping problem handled by each display or delivery pipeline.

Reference versus imitation

Citing ST 2084 as evidence that an image was mastered at extreme brightness would overstate the standard, which fixes an encoding relationship, not a mastering choice; and describing Hybrid Log-Gamma as simply an alternate name for Perceptual Quantization would contradict BT.2100's own presentation of them as two distinct, separately specified methods addressing the same HDR problem.

• Is PQ or ST 2084 being cited for the transfer function it defines, or as a stand-in for a specific creative brightness decision?
• Does a source correctly separate the PQ method from the HLG method rather than treating the two as one?
• Is the reaffirmed 2017 status of ST 2084 noted where its currency as a standard matters?

Together, the two standards establish a documented, dated technical boundary, how a mastering signal can represent very high luminance, and nothing about the visual character any production chose to put inside that boundary.