Ok i think i figured out why positive trim offset is ignored in TV-LED HDMI source. That value is the ''lift'' control in Resolve and unlike slope(gamma?) and power(gain?) , offset(lift) metadata will raise black bars if higher than 0.025(2100 in 12bit pq) and if the device doesn't use L5. So this means HDMI source will have worse quality than TVs internal player but lift is rarely used higher than 0.005. The positive offset metadata is 100% ignored, even values under 0.025 have no effect.
It doesn't make sense that the metadata is not ignored in LLDV though and I just tested on my LLDV devices and it does indeed raise letterbox black levels. Fake TV-LED devices also don't ignore positive lift.
test file without L5:
https://drive.google.com/file/d/1NgG1Zp ... drive_link
test file with L5:
https://drive.google.com/file/d/18eNbkD ... drive_link
https://www.youtube.com/watch?v=AVZ7xcgeEAM
NO L5:
PROPER L5 on device that use it:
Lift/Gamma/Gain: These controls function similarly to the Y-only Lift, Gamma, and Gain master
wheels of the Color Wheels palette, to let you trim the overall contrast levels of the image. The
Dolby Best Practices Guide recommends to limit positive Lift to no more than 0.025, and mostly
restrict yourself to using Gamma and Gain if necessary to lighten the image.
— Saturation Gain: Lets you trim the saturation of the most highly saturated areas within a scene.
Lesser saturated values will be less affected.
— Chroma Weight: Darkens saturated parts of the image to preserve colorfulness in areas of
the image that are clipped by smaller gamuts that don’t have enough headroom for saturation
in the highlights.
— Tone Detail: Lets you preserve contrast detail in the highlights that might otherwise be lost when
the highlights are mapped to lower dynamic ranges, usually due to clipping. Increasing Tone
Detail Weight increases the amount of highlight detail that’s preserved. When used, can have the
effect of sharpening highlight detail.
You can use Gamma to elevate the blacks/shadows as required and use the Gain trim control to restore any highlights that may have been elevated or clipped.
For example, if a program were graded relative to a 4000 nit display, along with a single 100 nit
BT.709 trim pass, then a Dolby Vision-compatible television with 750 nit peak output will reference
the 100 nit trim pass metadata in order to come up with the best way of “splitting the difference” to
output the signal correctly. On the other hand, were the colorist to do three trim passes, the first
at 100 nits, -cond at 600 nits, and a third at 1000 nits, then a 750 nit-capable Dolby Vision television
would be able to use the 600 and 1000 nit trim metadata to output more accurately scaled color
volume and HDR-strength highlights, relative to the colorist’s adjustments, that take better advantage
of the 750 nit output of that television.
