Calibrating HDR10

It’s been no secret up to now that calibrating a display for high dynamic range (HDR) is a work in progress. But the recent release of an HDR10 workflow for CalMAN 2016 (the newest software from SpectraCal) promises to change that. CalMAN is widely used by calibrators and reviewers to optimize display setup.

HDR10 is one of the two most prominent HDR formats (though there are others lurking around looking for a niche). Both of these formats require specialized, and different, calibration techniques. A CalMAN workflow for the other format, Dolby Vision, has been around for several months.

But most UHD/HDR sets offer HDR10, as do all UHD Blu-rays to date, making an HDR10 calibration perhaps even more significant—at least for now. Dolby Vision has, until recently, been used only by Vizio on the display side, and Dolby Vision content is available only from a few websites. LG’s new OLEDs, however, now offer both HDR10 and Dolby Vision and Dolby Vision might show up on UHD Blu-rays eventually. But HDR10 is mandatory for UHD Blu-ray; Dolby Vision is optional, but if it’s offered, HDR10 must also be included on the same disc.

The HDR10 workflow in CalMAN 2016 is still in Beta form, but Spectracal has informed us that it’s the organization of the workflow that’s subject to change, not the precision of the results it offers.

There are a few interesting results I’ve experienced so far, though they’re limited to calibrating a Samsung 65KS9800 SUHD set. A review of the latter is scheduled for an upcoming issue of Sound & Vision, so I won’t go into detail about it here. But a few points are worth mentioning.

With standard dynamic range on an LCD, at any useful average picture luminance, the peak white level doesn’t vary as the amount of screen space it occupies increases. We generally test for this with white window patterns, generally at 18% and 100%. But with a plasma, the peak brightness drops off as the signal fills more and more of the screen area. This is due to power supply limitations, as filling the screen with peak white demands more of the set’s power supply—and plasmas demanded a lot more juice than do LCDs. This “clamping” of the peak brightness, oddly, has no visible effect.

Why do I bring up plasmas, since they’re no longer part of the home video mix? Because with HDR, even an LCD’s power supply can be overtaxed as the brightness covers more and more of the screen. When fully calibrated, the Samsung’s white level measured 1351 nits (394 foot-lamberts) with a 100% white luminance window pattern covering 10% of the screen. Increasing the window size to 25% reduced this to 951 nits ( 278 ft-L), and increasing it to 100% dropped it further to 550 nits (161 ft-L).

As with SDR on a plasma, this has no obvious effect on the image. But it is significant because the size of the window pattern will affect the results of a calibration. CalMAN recommends using a 10% window for the test patterns, so this is the one that I used. I also calibrated the set’s HDR10 to the P3 D65 color gamut and selected SMPTE 2084 (these settings are found in the Source menu).

Calibrating HDR10 requires a special test pattern generator capable of producing HDR10 (and when needed, Dolby Vision) patterns. For my testing I used a Murideo Six-G (v1.77). The results of the tests will be published with our review, but for now I’ll only say that the set performed beautifully following calibration.

The default settings of the Standard Picture Mode, however, produced a poor result. For now I’ll only say, for the benefit of Samsung 65KS9800 owners who are hanging on my words here, that you can do worse in Standard Picture Mode if you set the Backlight to 19, the Brightness to 46, the Contrast to 92, and the Gamma to –1. The latter settings, at least on our sample, came very close to the proper luminance results at different levels. (The “gamma” for HDR is called the EOTF, for Electro Optical Transfer Function—there are people who make good money coming up with names like that!) I also turned the Color Tone from Standard to Warm2, turned Dynamic Contrast off, set Sharpness to 5, shifted Color Space from Native to Auto, and turned Auto Motion Plus Off.

But your best approach, especially for a flagship set such as this, would be to have a professional calibration. But check to be sure that your calibrator has experience in setting up a set for HDR. At this stage, not all calibrators have such experience. Like them, we are still stumbling a bit in the darkness when it comes to HDR. I believe I have a handle on it, but by my fingertips. As will all new formats, things do change.

WildGuy's picture

finally a new software that can show test patterns for HDR. its really cool that samsung flagship 65KS9800 led-lcd can output up to 1351 nits (394 ft-l) of brightness for 10% of screen area cover of a 100% white window.

its still amazing even at 100% of the screen covered, the brightness dropped off to 550 nits (161 ft-L).