One of the demos at Samsung’s QLED/HDR10 Summit last week was presented by SpectraCal, which is now part of Portrait Displays. The company’s CalMan software was automatically calibrating a Samsung Q9 TV. As seen in the photo above, CalMan was running on a laptop and calling up test patterns from a Murideo Six-G generator. A Klein K10A colorimeter was taking readings, and CalMan made the appropriate adjustments to the TV’s controls via RS232 (USB-to-RS232 adaptor on the computer connected to the TV’s headphone jack/serial port using an RS232-to-3.5mm cable). The laptop’s HDMI output was sent to a larger display so more people could see it in action.
A SpectraCal rep told me that this functionality should be available in CalMan in a few weeks. It only works with Samsung TVs at this point, but others will follow later this year. (Actually, CalMan can also auto-calibrate the Panasonic EZ1000 OLED TV, but it’s not available to consumers in the US. It is available to consumers in Europe, and professional users can get it in the US.)
Tyler Pruitt, Technical Liaison for SpectraCal, also offered an interesting presentation during the summit. Among his points were tips for calibrating HDR. In addition to CalMan software (of course!), you need to use a spectroradiometer or colorimeter that can handle HDR luminance and a pattern generator that supports ST 2086 (HDR10) metadata and BT.2020. Use test-pattern windows that cover no more than 10% of the screen, and exit all on-screen menus before taking measurements. These menus will affect the measurement, even if they do not extend into the measurement area. Finally, use RGB signaling, since BT.2020 uses a new 3×3 matrix for YCbCr that is not yet widely supported in pattern generators.
Speaking of pattern generators, he listed those that support HDR10:
– Murideo Six-G
– AccuPel DGA-6000
– SpectraCal VideoForge Pro (coming soon)
– Quantum Data 780, 804, 980 series
– Astro Design VG-876/877
Tyler also talked about some of the challenges to calibrating HDR. For example, there is no standard for HDR tone mapping, and the behavior of a TV changes based on metadata or analyzing video frames. As mentioned earlier, on-screen menus can affect measurements. Plus, there are no low-cost, consumer-oriented HDR10 pattern generators available yet.
Interestingly, all current HDR TVs are still gamma-based at the panel level. The HDR EOTF—known as ST 2084 or PQ—is mapped to the native panel gamma, and the calibration controls in current HDR TVs operate after this mapping.
In the future, Tyler hopes that TVs will offer the ability to disable HDR tone mapping, allowing you to calibrate the underlying panel gamma to the expected power function. For example, the Dolby Vision processor expects a panel gamma of 2.2, which it maps to PQ. If the actual panel gamma is not 2.2 throughout the luminance range, it won’t behave as intended when it receives HDR content. Once you calibrate the panel gamma and enable the TV’s HDR tone mapping, the DV processor will work as the manufacturer intended, and any panel variability will be eliminated.