Tyler Pruitt from SpectraCal, now part of Portrait Display, said that calibrating an HDR display is much harder than an SDR display. With HDR content, there is almost always a color volume remapping function in the TV that maps the luminance and colors of the content to the actual luminance range and color capabilities of the TV. Every company does this differently. Since the displays are still manufactured and tested with a gamma curve (not an HDR EOTF), additional adjustments need to be made to the signal. All this processing means it is really difficult to measure the actual native response of the panel instead of the combination of panel and processing.
To get around this, SpectraCal is working with LG Electronics and Dolby to develop a calibration procedure for HDR TVs specifically tailored for Dolby Vision content. The idea is to create a bypass mode that allows the native response of the panel to be measured and calibrated using a D65 white point and 2.2 Gamma. That then allows for the measurement of the maximum and minimum luminance measurements along with gamut primaries.
This, now specific, TV panel data can then be stored and used as input to the processing chain in the TV. Otherwise, a generic set of data is used from the factory floor instead of the actual performance of the specific panel being calibrated.
LG plans to store this reference file data on a USB stick, which must be inserted into the TV whenever Dolby Vision content is viewed.-CC
