HDR Reference White

In our blog post detailing the color correction workflow for HDR10, a reader asked where reference white and 18% gray should fall on the waveform monitor, and we incorrectly answered 100 nits for reference white and in the 40s for 18% gray. While typical white levels presently used in PQ production range anywhere from 145 – 250 nits, it is recommended that HDR Reference White (diffuse white) be 203 nits or 58% of the full PQ signal (input) level, as shown in the illustration below. It should be noted that 203 nits is only a recommendation for 1,000 nit peak brightness displays: that figure gets progressively higher for displays brighter than 1,000 nits.

If however, you’ve got graphics at 203 nits over a dark image, they may overpower the scene, whereas if the scene is very bright, the graphics may be difficult to see; larger areas of diffuse white may also appear brighter than a small area – which is why 203 nits is only a recommendation and not carved in stone!

“When creating text and graphics, it is important to prepare them for an HDR/PQ finish further downstream in the workflow as they can produce unexpected results. For example, white text/graphics created at code value 1023 (10bit) will appear as 100% white which is around 100 nits on a calibrated SDR display. This same text/graphic will again present itself at 100% white in PQ which would translate to 10,000 nits on a PQ display”. – Dolby