HDR10, Active HDR, Dolby Vision and other HDR schemes

[Robert Zohn]

I'm starting this thread for three reasons.

First, it's among the hottest, most discussed, and somewhat misunderstood but highly relevant subject to the new TV System that we are all beginning to embrace with significant growth among novices and enthusiasts alike.

Second, we have several HDR protocols and even requests from some manufacturers for changes to the SMPTE base standard HDR10 to add dynamic metadata and others who want to make it active without a standards change.

Third, is the misunderstanding of how HDR capable TVs tone map the various HDR systems to their luminance abilities.

Here's a kick start to this complex and fascinating subject.

Samsung has proposed a change to the SMPTE ST.2086 base standard HDR10 by adding dynamic metadata so it can perform much like Dolby Vision. Another very similar method that measures each frame on the fly and tone map the display to it's brightness capability, which is commonly called "active HDR".

LG and Sony are doing "active HDR" with the current base standard HDR10 on all of the 2017 X1 Extreme processor TVs, like the A1E OLED, Z9D, X940E and X930E, and LG employs a very similar active HDR10 processing with their SJ9500, C7, E7, G7 and W7 OLED TVs.

As I am more familiar with how Sony's active HDR10 operates I'll keep my comments to Sony's 2017 X1 Extreme models. You might notice very little difference between Dolby Vision and HDR10 on Sony's X1E equipped TVs. Sony HDR TVs don’t use the static brightness metadata in HDR10 (MaxCLL, MaxFALL) they actually measured brightness frame by frame and generate dynamic metadata for HDR10 content.

MaxFALL, stands for "Maximum Frame/Average Light Level" and MaxFALL corresponds to the highest frame average brightness of one frame from the entire content.

MaxCLL, is the Maximum Content Light Level and is an additional static HDR metadata that represents and measures the brightest pixel of the entire content.

In part this explains why the standard 10% peak luminance window test pattern may measure a lower peak luminance than what the display is actually capable to deliver when we view actual HDR content that only use a far smaller area of the screen with the HDR specular highlights that typically occupy less than 1% of the display.

This HDR anomaly is most noticeable when the content is mastered at 4k nits. In Sony's new 2017 X1 Extreme processor TVs the HDR algorithms are tuned to apply tone mapping (which reduces screen brightness and accuracy) when the brightness of the frame exceeds the TV set’s capabilities. It is then applied to ensure HDR highlights are properly displayed.

Let the discussion begin!