Perceptual quantizer
The perceptual quantizer, published by Society of [Motion Picture and Television Engineers|SMPTE] as SMPTE ST 2084, is a transfer function that allows for HDR display by replacing the gamma curve used in SDR. Its 0–1 value range represents luminance levels from 0 to 10,000 Candela [per square metre|cd/m2]. It was developed by Dolby and standardized in 2014 by Society of Motion [Picture and Television Engineers|SMPTE] and also in 2016 by ITU in Rec. 2100. ITU specifies the use of PQ or HLG as transfer functions for HDR-TV. PQ is the basis of HDR video formats and is also used for HDR still picture formats. PQ is not backward compatible with the BT.1886 EOTF, while HLG is compatible.
PQ is a non-linear transfer function based on the human visual perception of banding and is able to produce no visible banding in 12 bits. A power function extended to 10000 cd/m2 would have required 15 bits.
Technical details
The PQ EOTF is as follows:The PQ inverse EOTF is as follows:
where
- is the non-linear signal value, in the range.
- is the displayed luminance in cd/m2
- is the normalized linear displayed value, in the range