ITU Final HDR TV Spec Allows HLG, PQ ‘Options,’ Stipulates 3 Levels of Resolution
After three years of work, ITU finalized its new standard (BT.2100) for high-dynamic-range TV “that represents a major advance in television broadcasting,” the group said in a Tuesday announcement. BT.2100 builds further on the “superior colour fidelity” of ITU’s BT.2020 standard, ITU said.
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BT.2100 allows broadcast TV content “to take full advantage of the new and much brighter display technologies” by making “outdoor sunlit scenes appear brighter and more natural, adding highlights and sparkle,” ITU said. It also “enhances dimly lit interior and night scenes, revealing more detail in darker areas, giving TV producers the ability to reveal texture and subtle colours that are usually lost” with existing standard dynamic range TV, it said.
BT.2100 “details” the two prevalent “options” available for producing HDR content images, it said: the “perceptual quantization” (PQ) approach using an electro-optical transfer function newly updated and “finely tuned to match the human visual system,” and the hybrid log-gamma (HLG) specification, which offers “a degree of compatibility with legacy displays by more closely matching the previously established television transfer curves.” BT.2100 “also outlines a simple conversion process” between the two options, it said. Dolby Labs, Technicolor-Philips and the open HDR10 specification all use the PQ approach, while BBC and NHK are strong advocates of the HLG tack.
The new BT.2100 standard “also allows TV producers to choose from three levels” of resolution when creating HDR content -- 1080p (1920 x 1080), 4K (3840 x 2160) and 8K (7680 x 4320), ITU said. NHK is the world’s strongest advocate of 8K and plans to launch an 8K broadcasting service in Japan in time for the 2020 Tokyo Olympics. ATSC 3.0 currently stipulates broadcast resolutions up to 4K, but its framers say the suite of standards is flexibly designed to allow an upward migration path to 8K in the future. ATSC 3.0's framers recently completed several days of comparative HDR tests in New York and set a July 31 deadline for picking a winning HDR system, though some within the group are pushing for a two-month delay to Sept. 30 (see 1606160052).
As for HDR with 1080p, there seems growing sentiment in the engineering community in the U.S. that 4K resolution doesn't give the biggest bang for the buck for delivering HDR content via over-the-top or broadcast streams to the consumer. Many therefore favor pairing HDR with 1080p rather than 4K, partly on the grounds that 4K resolution is very bandwidth-hungry, a trend that was evident at a recent Society of Motion Picture and TV Engineers conference (see 1606290043).