Hybrid Log-Gamma (HLG)

Hybrid Log-Gamma (HLG) delivers HDR resolution without the need for metadata. This allows HLG to display well on SDR and HDR monitors.

Background

NHK and the BBC developed HLG in a joint effort to create a more compatible signal for a wide variety of television sets.

Hybrid Log-Gamma is an open-source standard HDR (High Dynamic Range) video format. Video dynamic range is the measurement between the brightness between black and white (luminosity).

Many monitors offer HDR. However, unlike resolution parameters (1080p, 4K, etc.), HDR is related to luminosity. Luminosity can vary between how an image is captured on a camera and how the image is broadcast to a monitor.

HDR, using Perceptual Quantizer (PQ), sends a signal along with metadata. This metadata is read by the monitor which then displays the signal using the luminosity information supplied by the metadata.

HLG sends a combination (hybrid) of the normal Gamma curve for light coding and a logarithmic curve to deliver the HDR aspects of the signal.