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Limit Range - A unique approach to PQ HDR Calibration

Author Steve

#1 | Posted: 15 Apr 2021 22:40 | Edited by: Steve 
One of the issues with PQ HDR is Display Calibration...

The present default approach is to disable the PQ EOTF, resorting to a 2.2 Power Law Gamma, and profile from scratch, in what is effectively super bright SDR mode.
And the very large EOTF change from gamma 2.2 to the PQ EOTF often makes for inaccurate calibration, especially with inferior calibration systems.
(ColourSpace actually doesn't suffer this issue.)

Additionally, some PQ HRD displays respond very differently when set to a 2.2 power law gamma in super bright mode, vs. using a PQ HDR EOTF...

But, traditionally, trying to calibrate PQ HDR display without removing the PQ EOTF means a lot of the profile data is thrown away, as it is above the peak nits limit of the display, as PQ HDR is an Absolute standard.

So, working with or friends at Flanders Scientific, we developed a PQ HDR calibration method that can be applied to a display with a fixed/burnt-in PQ EOTF, effectively calibration on-top of it, as we do with SDR calibration already.
(All SDR displays have a default 2.2 gamma EOTF, on-top of which the final accurate calibration is applied.)

This means the displays is actually profiled and calibrated while being in PQ HDR mode.

FSI have actually been using this approach for a while, using a slightly complicated manual workflow,
With the next release of ColourSpace we have introduced the first stage of a more simplified procedure.
After some user feedback, a second stage will be implemented, making the calibration approach even simpler.

The benefit is all profile data - the measured patches - are used in the final calibration LUT, and the display responds consistently throughout profiling and calibration..

The Interactive User Manual, and the Patch Scale & Resolution pages of the website have already been updated with overview info/instructions on the new Limit Range capabilities.


The same approach can also be used with standard SDR/HLG calibration, should there be a need to limit the patch range...

Steve Shaw
Mob Boss at Light Illusion

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 Limit Range - A unique approach to PQ HDR Calibration

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