600 Nits Seems To Be The Magic Number

We’ve remarked before how the figure 600 seems to crop up every time a colorist is asked about the peak nits of their projects. Here are a couple more data points.

Cullen Kelly: Do you impose a hard speed limit on your projects?

Corinne Bogdanowicz: I don’t have a hard rule or setting that I use. [It] depends on the project. I rarely peak things at 1000 nits. Most people don’t react well to things being that bright. I generally start with a roll off but I could still go up to 600 nits. If it’s a much softer show, we’ll maybe do 300 nits – maybe even less. But again, it might change scene to scene. There might be some brighter scenes, there might be some scenes that are softer, so it just kind of depends on what we’re doing.” Bogdanowicz uses Sony BVM-HX310 and BVM-X300 monitors and a PVM off to the side for Rec.709.

Or take this one:

“For the HDR, general peak brightness was 600 nits, with sporadic 1,000 nits sparks; Most of the show sits around 150-250 nits and was mastered on the Sony BVM-X300/2 monitor.” – Juan Cabrera on the color workflow and look development of the Netflix series “Mo”

While many streaming network shows are graded to around 600 nits, few colorists or cinematographers are able to articulate precisely why.

John Daro, Senior Colorist at Warner Bros, once wrote, “There is no set standard for what is considered HDR brightness. I consider anything over 600 nits HDR.”

There’s little question that where diffuse white sits plays a crucial role in deciding the peak luminance. The reason for this is hinted at in the following statement by SMPTE, the closest the organization ever got to defining what HDR is: “A High Dynamic Range System (HDR System) is specified and designed for capturing, processing, and reproducing a scene, conveying the full range of perceptible shadow and highlight detail, with sufficient precision and acceptable artifacts, including sufficient separation of diffuse white and specular highlights”. The key words are sufficient separation – but how much separation is sufficient? Charles Poynton once said that specular highlights ought to be 3x diffuse white, but we believe he later wisely revised that figure to 5-10x diffuse white.

Which brings us right back to diffuse white. Didn’t the International Telecommunications Union already establish standards for HDR Reference White? LG Electronics wrote that despite “ITU recommendations, most theatrical and episodic HDR content does not have a diffuse white level of 203 nits. The diffuse white level in such content usually changes from scene to scene, and is far closer to the typical diffuse white level of SDR content of between 80 and 100 nits at most.” So, if a show’s diffuse white falls around ~ 100 nits or so, then 600 nits – give or take – ought to be sufficiently bright to convincingly make emissives and speculars appear as highlights.