Issue link: https://digital.copcomm.com/i/851458
www.postmagazine.com 34 POST JULY 2017 4K HDR AND separating digital production formats from imaging attributes BY LARRY THORPE SENIOR FELLOW IMAGING TECHNOLOGIES & COMMUNICATIONS GROUP PROFESSIONAL ENGINEERING & SOLUTIONS DIVISION 1 CANON USA MELVILLE, NY USA.CANON.COM ver the past two decades, a range of digital production for- mats has been standardized for video motion imaging. They emerged on two fronts — one, being televi- sion-centric and the other digital cin- ema-centric. Television had seen very protracted standardization activities in the quest to transition from standard definition television (SDTV) to high definition television (HDTV). The asso- ciated digital formats are traditionally identified by the horizontal and vertical digital sampling structures that define a single video frame. They constitute a container suffi- cient to encompass the sought-for increased resolution. The standards further specify a prescribed range of frame rates that determine the tempo- ral resolution of the production format. The other component of that digital structure is the choice of bit depth — referred to as digital quantization. For high definition (HD), two primary production formats emerged: 1920 (H) x 1080 (V) with a specified range of frame rates (progressive and interlace), and the 1280 (H) x 720 (V) progres- sive-only standard. Over the past decade, there arose high activity in developing new stan- dards that would define video produc- tion systems having resolutions con- siderably beyond those of HD. One of these has twice the horizontal and ver- tical samples as HD — and is identified as 3840 (H) x 2160 (V) — sometimes termed 4K UHD but more often is UHD. The second format has twice as many again — and is identified as 7680 (H) x 4320 (V) — or 8K UHD. For the past 25 years, the highest priority has been to sequentially elevate resolution. Separate to HD and UHD stan- dardization, there arose an activity to standardize the emerging digital cinema. This entailed creating produc- tion standards for origination of motion picture as well as infrastructural stan- dards (in support of movie distribution) and projection standards for the digital theaters themselves. These standards ultimately emerged from the SMPTE and are slightly different to the HD and UHD television standards. The 2K cine standard has a sampling structure of 2048 (H) x 1080 (V) and the 4K cine standard has 4096 (H) x 2160 (V) digi- tal samples. VIDEO IMAGING ATTRIBUTES — HDR AND WCG Allied with the structural specifications of the digital video signals are imaging attributes that collectively contribute to the overall quality of the picture. These attributes include definitions of the color reproduction (specific range of colors that can be supported and is referred to as color gamut), and tonal reproduction (specific dynamic range or contrast that is supported). Dynamic range is an imaging attri- bute well understood in the cinema- tography world. Motion picture film negative traditionally had an impressive dynamic range (film print less so) that greatly exceeded the range achievable in television over most of its history — including the first decade of HDTV. But a variety of technological devel- opments over the past decade have significantly extended the dynamic range capabilities of television displays. On the camera front, equally impressive developments in image sensors sup- ported a rapid advance in the dynamic range capabilities of contemporary video cameras — especially in the large format Super35mm category. These advances triggered an industry ex- ploration of the visual promise of high dynamic range — meaning significantly beyond what we have been accus- tomed to in HDTV — and now known affectionately as HDR. HDR seeks increased detail reproduction in both highlight and lowlight regions of a given image. On the color reproduction front, the associated colorimetry standards had long been enslaved to the capabilities of the CRT television displays, which always sought a balance between image brightness and color gamut. But again, the past decade has been witness to astonishing developments in displays (all non-CRT like LCD, plasma, OLED, etc.) in terms extensions to their range of reproducible colors. Cameras and lenses capitalized on this and started to widen their color gamuts. The term "wide color gamut" summarized all of these efforts — now known as WCG. Standardization stepped in again and in 2015 the ITU published its ITU Rec. BT.2020 standard for the two flavors of UHD — with each of them having a significantly wider color gamut than today's HDTV. One regularly hears today of "2020 color." Finally, in the summer of 2016, the ITU published its HDR standard — iden- tified as Rec BT. 2100. It recognized the two industry approaches to HDR — one being the Perceptual Quantization (PQ) system developed largely by Dolby (and tailor-made for pre-recorded productions like movies and episodic television), and the separate Hybrid Log Gamma (HLG) system developed by broadcasters BBC and NHK (tai- lor-made for passage through broadcast infrastructures and for live television). What is most important about this standard is its agnosticism with respect to digital production formats. The specified HDR applies equally to 1080P, 2160P, and 4320P. Note all are pro- gressive scanning formats. O