EOTF — Electro-Optical Transfer Function
Definition
The EOTF (electro-optical transfer function) is the function that converts the code values of a video signal into light emitted by the display. For SDR, ITU-R BT.1886 defines a reference EOTF close to a 2.4 power law for studio displays, while displays for brighter environments and computers often use about 2.2. For HDR, ITU-R BT.2100 defines PQ (SMPTE ST 2084), which maps code values to absolute luminance up to 10,000 cd/m², and HLG, which is relative to the display's peak luminance and compatible with SDR. When the EOTF set on a display differs from the one used to master the content, the image looks washed out or crushed; it is a common HDR setup error.
In the field
HDR content that looks flat and grey usually means the display is still set to SDR gamma. The EOTF (PQ, HLG or gamma) is aligned across the source, each processor and the display before the picture is judged. Automatic detection relies on the HDR InfoFrame defined in CTA-861.3, which some matrices, extenders and scalers do not pass through.
Sources
- ITU-R BT.1886 : EOTF de référence des écrans plats de production HDTV, loi de puissance 2,4 · itu.int
- ITU-R BT.2100-3 : EOTF PQ (jusqu'à 10 000 cd/m²) et HLG · itu.int
- Wikipédia, Perceptual quantizer : PQ normalisé dans SMPTE ST 2084 (pointeur secondaire) · en.wikipedia.org
- Wikipédia, HDR10 : PQ, métadonnées statiques SMPTE ST 2086, MaxCLL et MaxFALL (pointeur secondaire) · en.wikipedia.org
- CTA-861.3, HDR Static Metadata Extensions : InfoFrame Dynamic Range and Mastering et bloc EDID de signalisation HDR · shop.cta.tech