User Manual

Finally, ST.2084 has been included inthe HDR 10 standard adopted by the Blu-ray Disc
Association (BDA) that covers Ultra HD Blu-ray. HDR 10 stipulates that Ultra HD Blu-ray discs
have the following characteristics:
 UHDresolution of 3840 x 2160
 Up to the Rec. 2020 gamut
 SMPTE ST.2084
 Mastered with a peak luminance of 1000 nits
The downside is that, by itself, an HDR10 mastered program is not backward compatible with
Rec. 709 displays using BT.1886 (although theemerging HDR10+ standard described later
addresses this). Furthermore, no provision is made to scale the above-100 nit portion of the
image to accommodate different displays with differing peak luminance levels. For example, if
you grade and masteran image to have peak luminance of 4000 nits, and you play that signal
on an HDR10-compatible television (using ST.2084) that’s only capable of 800 nits, then
everything above 800 nits will be clipped, while everything below 800 nits will look exactly as
it should relative to your grade.
This is because ST.2084 is referenced toabsolute luminance. If you grade an HDR image
referencinga 1000 nit peak luminance display, as is recommended by HDR10, then any display
using ST.2084 will respect and reproduce all levels from the HDR signal that it’s capable of
reproducing as you graded them, up to the maximum peak luminance level it can reproduce.
For example, on an HDR10-compatible television capable of outputting 500 nits, all mastered
levels from 501–1000 will be clipped, as seen in the screenshot below.
Comparing the original 1000 nit waveform representing the grading monitor
to a 500 nit clipped waveform representing the consumer television
How much of a problem this is really depends on how you choose to grade your HDR-strength
highlights. If you’re only raisingthe most extreme peak highlights to maximum HDR-strength
levels, then it’s entirely possible that the audience might not notice that the display is only
Chapter – 8 HDR Setup andGrading 253