The Video Electronics Standards Association (VESA) has defined the display industry’s first fully open standard specifying high dynamic range (HDR) quality, including luminance, color gamut, bit depth and rise time, through the release of a test specification. Note the word open – a jab at the Ultra High Definition Alliance’s (UHDA) Premium specification that discloses the top level specifications, but not guidance on how those metrics are measured for independent validation. VESA has addressed this by creating three classes of HDR display with minimum specifications and the detailed test methodology to validate performance. We believe such transparency is good for the industry.
The new VESA High-Performance Monitor and Display Compliance Test Specification (DisplayHDR) initially addresses the needs of laptop displays and PC desktop monitors where HDR is gaining interest for a wide range of applications including movie viewing, gaming, and creation of photo and video content. DisplayHDR v1.0 focuses on LCDs, which represent more than 99 percent of displays in the PC market. VESA anticipates future releases to address organic light emitting diode (OLED) and other display technologies as they become more common, as well as the addition of higher levels of HDR performance.
VESA developed the DisplayHDR specification with the input of more than two dozen active member companies. These members include major OEMs that make displays, graphic cards, CPUs, panels, display drivers and other components, as well as color calibration providers.
With DisplayHDR, VESA aims to alleviate HDR logo confusion by:
- Creating a specification, initially for the PC industry, that will be shared publicly and transparently
- Developing an automated testing tool that end users can download to perform their own testing if desired
- Delivering a robust set of test metrics for HDR that clearly articulate the performance level of the device being purchased
The specification establishes three HDR performance levels for PC displays: baseline (DisplayHDR 400), mid-range (DisplayHDR 600) and high-end (DisplayHDR 1000). These levels are established and certified using eight specific parameter requirements and associated tests, as shown in the table below.
Note that there are also comments next to each measurement that describes why this metric is included. This is extremely helpful and educational.
“We selected 400 nits as the DisplayHDR specification’s entry point for three key reasons,” said Roland Wooster, chairman of the VESA task group responsible for DisplayHDR, and the association’s representative from Intel Corp for HDR display technology. “First, 400 nits is 50 percent brighter than typical SDR laptop displays. Second, the bit depth requirement is true 8-bit, whereas the vast majority of SDR panels are only 6-bit with dithering to simulate 8-bit video. Finally, the DisplayHDR 400 spec requires HDR-10 support and global dimming at a minimum. With this tiered specification, ranging from baseline to high-end HDR performance levels, PC makers will finally have consistent, measurable HDR performance parameters. Also, when buying a new PC, consumers will be able to view an HDR rating number that is meaningful and will reflect actual performance.”
In a follow-up conversation with Wooster, he explained that the categories contain minimum specifications so some products may exceed these minimums. The levels were carefully set with input for the main contributors to correspond with existing products and capabilities. He explained that developing these open metrics and the associated test methodology contained in a separate document called VESA High-performance Monitor and Display Compliance Test Specification (DisplayHDR CTS), was a very important goal of the effort. “Ordinary consumers or end users can validate the HDR specifications using this document and an inexpensive colorimeter,” said Wooster. “Compliance testing adds some additional requirements on the level of the test gear, however. Test labs, reviewers, competitors and others will have such gear so conformance can be checked by many people. VESA will also have an audit procedure to check that the manufacturers are adhering to their self-declared performance level.”
Why no Audio?
So why is resolution and audio not part of the specification? “In the PC market, there is a range of screen resolutions and aspect ratios and audio may very well be an external component,” explained Wooster. HDR can have a visual impact regardless of resolution, so the contributors did not want to limit this aspect. In reality, we think most HDR displays will be FHD at a minimum.”
Bit depth is not often discussed as a specification with HDR displays, so why did you include this, we asked? “There is a lot of misunderstanding about bit depth,” continued Wooster. “SMPTE specifies a 10-bit input signal, which we do as well, but the image processing and display drivers may not maintain that bit depth. Many displays that are claimed to be 10-bit, including some TVs, are actually using 8-bit image processing and panel drivers that are 8-bit plus 2 bits of dithering to simulate a 10-bit image. This can work quite well, but it not the same as true 10-bit pipeline. We require a minimum for 8-bits per color for image processing (not 6 bits and 2 bits of dithering which is common in SDR displays) and 8 bits minimum for the digital-to-analog display drivers, with 10 bits desirable for the 600 and 1000 levels as banding artifacts become more visible at higher luminance levels.”
Why 99% of 709 and not 100%? “We wanted to push for 100% but the manufacturing tolerances are such today that the manufacturers were only comfortable with this 99% level. But, that is already a lot higher than most PC displays,” said Wooster.
Any thoughts on doing tests with a room ambient lighting? “Performance here will be very influenced by the screen reflectivity. We have not considered this yet, but may do so in the future,” said Wooster.
What about support for dynamic metadata content in an HDR10+ or Dolby Vision format? “Since this specification is geared toward PC-based products like laptops and monitors, it is the GPU that will have to decode any dynamic metadata and adjust the video signal based upon the capabilities of the attached display,” explained Wooster. “That is a function that is not something we can control or specify.”
Also ground breaking is the specification of the rise time of the backlight. Two scenarios are well explained in the table below. Problems may arise if the backlight control is not well synchronized with the video playback. The DisplayHDR CTS document then explains how to do this measurement with a maximum of 8 frames delay requirement.
The new spec can be downloaded for free. Get more information and the download link at: https://displayhdr.org/.
New products complying with the DisplayHDR specification will be demonstrated at the Consumer Electronics Show (CES), January 9-12, 2018 at the Las Vegas Convention Center South Hall, DisplayPort booth #21066 –
Analyst Comment
The DisplayHDR CTS is very well constructed with clear test methodology and rationale for each test. CC
