Overview: Transfer functions

Transfer functions describe relationships between encoded signal values and light at different stages of image creation and display.

Camera encoding, display output and the overall picture transform describe different relationships. OETF, EOTF and OOTF identify those stages, while gamma, BT.1886 and PQ describe particular conventions within that vocabulary. Understanding the stage makes brightness signaling and HDR interpretation much easier to discuss precisely.

• Electro-optical transfer function (EOTF)
  An EOTF maps an encoded picture signal to the light a display should produce.

• Opto-electronic transfer function (OETF)
  An OETF maps scene light into the nonlinear signal used to represent a captured image.

• Opto-optical transfer function (OOTF)
  An OOTF describes the overall relationship between scene light and the light reproduced by a display.

• Video gamma
  Video gamma describes power-law relationships used to encode or display image brightness.

• ITU-R BT.1886
  ITU-R BT.1886 defines a reference SDR display response using a 2.4 exponent and the display black and white levels.

• Perceptual Quantizer (PQ): SMPTE ST 2084
  PQ is an HDR transfer function that assigns encoded signal values to absolute light levels up to 10,000 nits.

References

• SMPTE ST 2084: HDR reference display transfer function
• ITU-R BT.709-6: HDTV parameters
• ITU-R BT.2100-3: HDR television parameters
• ITU-R BT.1886: Reference display transfer function