At Display Summit in June, one of the sessions was titled “Pushing Color, Dynamic Range and Frame Rates.” For anyone interested in improving the viewer experience of UHD displays, the three presentations in this session were eye opening. In addition, there was a short session titled “Improving the Projected Image,” also important with people concerned with image quality.
The Ultimate UHD TV System
Joe Kane (Joe Kane Productions) presented a talk titled “The Ultimate UHD TV System.” Mr. Kane specializes in the sciences of electronic imaging and accurately reproducing video signals on display devices. He’s a very standards-oriented person, and believes, for example, the colorimetry of a display should match the colorimetry of the video standard of the content being shown. If the content is based on Rec. 709 (HDTV) colorimetry, the display should have Rec. 709 color primaries.
While this approach sounds obvious, it is not always accepted and hardly accepted at all in the world of mass-market consumer electronics. Part of the problem is Rec. 709 colorimetry, which is used in HDTV worldwide, actually has a relatively small color gamut. It not only cannot reproduce all the colors in the real world, it cannot reproduce the added colors animators, special effects people and consumers would like to see on TV.
While Mr. Kane supports the use of displays with Rec. 709 for displaying content encoded with Rec. 709, he is well aware of its shortcomings and spent a large part of his talk discussing both those shortcomings and color gamuts for future display systems and transmission standards.
In the left hand figure, Kane shows the original NTSC color gamut, based on CRT phosphors available in 1953, compared to the gamut of real surface colors, which are the reflective colors you see on real objects under white light. Even this relatively large gamut doesn’t cover all surface colors, let alone all the colors of emissive objects (he used photos of flowers and signage of Las Vegas as examples) and artificial colors that special effects people would like to put into content.
The three very similar color gamuts in the center are also based on CRT phosphors, but ones that are more efficient than the original NTSC phosphors, especially in the green. EBU is used in Europe for SD, SMPTE “C” is used in the US for SD and Rec. 709 is used worldwide for HD (1080p and 720p).
Rec. 2020 was approved by the International Telecommunication Union (ITU) for UHD or 2160p (Kane’s preferred term) in 2012 for broadcast applications. It includes more than just colorimetry, but the colorimetry aspect of Rec. 2020 is what Kane focused on.
Kane sees two problems with the Rec. 2020 colorimetry standard. (Note: no current UHD TV or home theater projector has a Rec. 2020 color gamut.) First, it is still a limited color gamut and cannot produce all colors people would like to put into content. This is true even though the Rec. 2020 color gamut is, in fact, larger than the digital cinema color gamut….
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