[RFC PATCH v3 1/6] drm/doc: Color Management and HDR10 RFC

[Harry Wentland]

On 2021-09-20 20:14, Harry Wentland wrote:
> On 2021-09-15 10:01, Pekka Paalanen wrote:> On Fri, 30 Jul 2021 16:41:29 -0400
>> Harry Wentland <harry.wentland at amd.com> wrote:
>>

<snip>

>>> +If a display's maximum HDR white level is correctly reported it is trivial
>>> +to convert between all of the above representations of SDR white level. If
>>> +it is not, defining SDR luminance as a nits value, or a ratio vs a fixed
>>> +nits value is preferred, assuming we are blending in linear space.
>>> +
>>> +It is our experience that many HDR displays do not report maximum white
>>> +level correctly
>>
>> Which value do you refer to as "maximum white", and how did you measure
>> it?
>>
> Good question. I haven't played with those displays myself but I'll try to
> find out a bit more background behind this statement.
> 


Some TVs report the EOTF but not the luminance values.
For an example edid-code capture of my eDP HDR panel:

  HDR Static Metadata Data Block:
    Electro optical transfer functions:
      Traditional gamma - SDR luminance range
      SMPTE ST2084
    Supported static metadata descriptors:
      Static metadata type 1
    Desired content max luminance: 115 (603.666 cd/m^2)
    Desired content max frame-average luminance: 109 (530.095 cd/m^2)
    Desired content min luminance: 7 (0.005 cd/m^2)

I suspect on those TVs it looks like this:

  HDR Static Metadata Data Block:
    Electro optical transfer functions:
      Traditional gamma - SDR luminance range
      SMPTE ST2084
    Supported static metadata descriptors:
      Static metadata type 1

Windows has some defaults in this case and our Windows driver also has
some defaults.

Using defaults in the 1000-2000 nits range would yield much better
tone-mapping results than assuming the monitor can support a full
10k nits.

As an aside, recently we've come across displays where the max
average luminance is higher than the max peak luminance. This is
not a mistake but due to how the display's dimming zones work.

Not sure what impact this might have on tone-mapping, other than
to keep in mind that we can assume that max_avg < max_peak.

Harry