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@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