A true PQ curve is an absolute cv-nit scale. The normalized CVs of a few different nit levels are:

100 nit = 0.5081
600 nit = 0.6963
1000 nit = 0.7518
4000 = 0.9026

Here's Steve Shaw's write-up on the matter which further backs up my concerns: https://www.lightillusion.com/uhdtv.html

This behavior is how reference displays should work (notwithstanding HDR metadata and consumer-grade secret-sauce), and I can confirm is the way the Dolby Pulsar, Sony x300, and x550 all work. When fed RGB(.5081, .5081, .5081) on all three displays set to D65 ST2084, you should measure 100 nits. If you feed a linear ramp to all the displays, you will see a hard clip of all values above the associated code value for that display's peak luminance.

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Apple's document 

HDR and Wide Color Gamut in Final Cut Pro 

White Paper November 2020

says:

====

Wide Color Gamut Displays that support wider color gamuts with a traditional luminance range are sometimes referred to as wide-gamut, standard-dynamicrange (SDR) displays. Current models of Mac, iPhone, and iPad support a wider-gamut SDR color space called Display P3. Display P3 uses the same color gamut as DCI P3, the standard for movie theater digital projectors, combined with a white point and gamma appropriate for typical viewing environments. The figure below shows that the P3 color gamut contains more colors than the Rec. 709 gamut, with notable improvements in the range of red and green areas of the color spectrum.

[..]

High Dynamic Range Displays that support both wider color gamuts and higher luminance ranges are referred to as high-dynamic-range (HDR) displays. HDR displays can produce not only high peak luminance values but also very low black levels, revealing more detail in both shadows and highlights. HDR displays typically reach peak brightness levels above 1000 nits while maintaining very high contrast ratios, much higher than the brightness levels and contrast ratios of SDR displays. These levels of brightness mean that images appear more true to life, with a dynamic range that more closely reflects what the eye sees in the real world. The figure below shows how increased brightness levels (measured in nits) combined with a wider color gamut greatly expand the range of reproducible color. 

HDR displays typically process video at 10 bits per color component rather than 8 bits. The additional color data lets HDR displays render more discrete steps from the minimum to maximum brightness value in each color. In order to encode and transmit HDR images more efficiently, new mathematical transfer functions are used instead of gamma. Two popular standards are the Perceptual Quantizer (PQ) function, defined in both SMPTE ST 2084 and ITU-R Recommendation BT.2100, and Hybrid Log-Gamma (HLG), also defined in Rec. 2100.

About Changing a Project’s Color Space After you set a library to wide-gamut HDR, any project with HD resolution or higher created in that library can be set to one of the following color spaces using the Modify command in the Project Properties inspector (described in step 3 above): 

• Standard - Rec. 709 

• Wide Gamut - Rec. 2020 

• Wide Gamut HDR - Rec. 2020 PQ 

• Wide Gamut HDR - Rec. 2020 HLG

[..]

When performing these adjustments, it may be helpful to show the Waveform video scope and set it to either RGB Parade or RGB Overlay view. In these views, the vertical axis of the waveform is labeled in units of cd/m2 (nits), which is a measure of the display’s output brightness level corresponding to the PQ signal level. Note that for the Luma and Chroma views, and for any non-PQ content, the vertical axis reverts to IRE (where 100 IRE represents 100% signal level). This is because the waveform signal in these cases does not correspond directly to  absolute cd/m2 values.

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So, it seems that we currently lack easy user choice between PQ/HLG variants of Wide Gamut bt 2020 color space, I think in ffmpeg/swscale they hide as "trc" (transfer curve) ... but I can be wrong.

Also tonemapper on cpu, at least on my potato,  tend to be slow, unless you downscale to like 1/4 out of 4k source?

So it will be helpful to look into vf_libplacebo, opencl_tonemap etc on machines where they work.

Sorry if it feels like too much of confusing info, I think while technically cingg currently  capable of *encoding* at least some variants of HDR -  more accurate displaying, easy user settings, waveform scope  display "morphing" to HDR mode, HDR10+ dynamic metadata calculations all missed, relative to FCP/Resolve.