Affordable HDR Conversion with SL-HDR1 Metadata a Cobalt Digital White Paper

Affordable HDR Conversion with SL-HDR1 Metadata A Cobalt Digital White Paper

By Ciro A. Noronha, Ph.D.

High Dynamic Range (HDR) is an emerging technology that delivers noticeably better image quality than standard dynamic range (SDR) content with minimal bandwidth increase. However, while HDR continues to gain popularity, SDR needs to be preserved – at least for the near future – because a large number of legacy consumer televisions do not support HDR. Acknowledging the mix of HDR and SDR devices in the marketplace, this white paper will examine different ways to provide cost- effective, simultaneous service to both types of devices, and explain why the SL-HDR1 conversion option is an ideal choice for broadcasters.

Luminance and Wide Color Gamut

Dynamic range is the ratio between the approximately 100:1. Dynamic range is usually lowest and highest values of the luminance, expressed in stops, which is calculated as or intensity of light emitted, from a display. the log base 2 of the ratio. So, 8-bit SDR has a Essentially, it is the ratio between the “whitest dynamic range of approximately six stops, while white” and “blackest black.” Conventional 8-bit professional 10-bit SDR offers approximately 10 displays, for example, have a dynamic range of stops. The human eye, however, can see about 12- higher range. Fundamentally, HDR shows more 14 stops, which means it can perceive more detail in the bright areas. dynamic range than offered by 10-bit SDR material. So, how do you pack an HDR signal Light intensity is measured in candelas per into a 10-bit display? Thankfully, the human square meter (cd/m2), also known as nits. A eye is nonlinear in its response and perceives standard HDTV can produce luminance at about more detail at lower luminosities. HDR delivers 100 nits. A UHD LCD display can range from images with improved details by assigning bits 0.05 to 1,000 nits, while a UHD OLED monitor to light intensity in a nonlinear manner. More can produce 0.0005 to 540 nits. In contrast, bits are assigned to the lower intensities and HDR can code up to 10,000 nits, which no fewer bits to the higher intensities to express a commercial monitor today can reproduce.

The diagram above shows a representation of the full range of light the human eye is capable of seeing. HDR is able to retain a greater range of light than SDR from capture to final distribution. Pictures are more vibrant and life-like to the viewer, regardless of screen size.

The luminance encoded in SDR signals is three defined color spaces in use today: ITU-R relative – at 100 percent, it basically tells the BT.709, which is considered the standard color display to show its whitest white. In contrast, space for HD; DCI-P3, which is the standard for HDR codes the absolute value of the luminance, digital cinema; and ITU-R BT.2020, which is the using a non-linear transfer function based on UHDTV standard. what the eye can perceive. This is the SMPTE 2084 Perceptual Quantizer (PQ) transfer. No commercial monitor today can display the full Rec. 2020 color space, but a UHDTV with Beyond luminance, HDR also features wide HDR and WCG will show more than the entire color gamut (WCG), which has more color Rec. 709 color space and at least 90 percent information than standard HD signals. The of the DCI-P3 color space. But what happens set of colors a signal uses or a display can when a display is fed an HDR signal it cannot show is called the “color space.” There are display because the luminance and/or color The objective of dynamic metadata is the same, but it changes from frame to frame. Static metadata can be seen as sort of an average over the content, while dynamic metadata is tailored to each individual frame. This dynamic metadata is one of the ways the various HDR standards differ.

HDR Standards

There are a number of competing HDR standards available today, and most of them provide some support for simultaneous SDR and HDR support. From a high-level point of This graph is a representation of the color gamut. The orange triangle represents REC.709 or 35.9% coverage. view, they can be classified as static (using The green triangle represents REC.2020 which is 75.8% static metadata or no metadata) and dynamic coverage. (using dynamic metadata). are out of range? The monitor must create The baseline HDR support starts with the an image as close as possible to the original SMPTE 2084 PQ transfer function, using 10-bit source material – and to help the monitor or 12-bit samples. This is the basis for most do this job, metadata may be included in the HDR standards, and by itself does not include stream. Metadata helps the monitor adapt the any support for SDR. The HDR10 standard is absolute luminance of the HDR signal to its simply the combination of SMPTE 2084 with 10- capabilities. bit samples and SMPTE 2086 static metadata; this combination is also standardized in ATSC Static Vs. Dynamic Metadata A/341.

Metadata can be static or dynamic. Static Static vs Dynamic Metadata metadata, as the name implies, is fixed for the duration of the content, and provides only “general” information. The basis for static metadata is SMPTE 2086. When content is created, it is mastered on a reference display by the director/colorist. The static metadata describes the characteristics of this mastering display, so that the monitor currently playing it can best approximate the mastering display based on its capabilities. SMPTE 2086 static metadata includes parameters such as the color and luminance range of the mastering display, the color space used, and the transfer characteristics. SMPTE 2086 was augmented by CTA to include additional parameters such as the Maximum Content Light Level (so the Static metadata provides only one metadata value monitor will know the “brightest” pixel in the while dynamic metadata provides a different metadata content) and the Maximum Frame-Average value for each frame of video. Light Level. One interesting static HDR standard that is device needs to understand and process the in wide use today is Hybrid Log-Gamma (HLG), metadata in order to do so. which is not based on SMPTE 2084 PQ. It is an attempt to use a backward-compatible transfer With SL-HDR1, the opposite happens. What curve that will “work” with both SDR and HDR is transmitted is a standard SDR signal, and monitors without any metadata. At the low the metadata allows a compatible device to luminance levels, it matches SDR, so an HLG reconstruct the original HDR signal (or any signal applied to an SDR monitor will “look OK”, intermediate level suitable for its capabilities). which an HDR monitor will show the improved This is the ideal way to support legacy SDR ranges at the higher luminance levels. HLG devices – they will just ignore the metadata trades off simplicity (same signal everywhere, (because they do not support it) and simply no metadata processing) with quality (it is not display the SDR image. This is conceptually the as good as the dynamic metadata options). same as what was done when analog color TV HLG is standardized in ARIB STD B-67, ITU-R was introduced. The signal was the standard BT.2100, and ATSC 3.0. black-and-white content, with the color information added “on the side”. A black-and- The dynamic HDR standards all start from a PQ white TV would understand the signal and show base layer, with metadata defined in ST 2094- the black-and-white version, while a newer 1. The most relevant ones are SMPTE 2094- color TV would extract the color information 10 (Dolby Vision), SMPTE 2094-40 (HDR10+, a and show a color picture. dynamic version of HDR10), and SL-HDR1. To support a mix of SDR and HDR devices, broadcasters have several options. First is HDR-to-SDR Conversion Options simply simulcasting two or more versions of the same signal, one in HDR and one in SDR. The basic operation of various dynamic Simulcast is well suited for OTT distribution, standards can be understood as transmitting where multiple versions of the same content “an image plus instructions” that can be are already required. It is also the only processed by a monitor. What varies is what real solution for supporting legacy 8-bit you start from. In Dolby Vision and HDR10+, you devices, such as AVC 4:2:0 decoders, because start with an HDR image, and the “instructions” HDR requires 10-bit performance to avoid allow the mapping of that HDR image to any posterization. monitor, all the way down to an SDR monitor. HLG is another option, as the same signal is While it is possible for an end device to compatible with both HDR and SDR. However, generate SDR from this HDR signal, that end this can negatively impact the quality of the SL-HDR1 Workflow

Source: ETSI TS 103 433-1 The SL-HDR1 workflow allows for simultaneous HDR and SDR delivery with just a single SDR output with metadata from the encoder. A downstream receiver determines HDR or SDR playout. HDR signal, unless the distributor controls the in the VANC using SMPTE 2108 for SDI. production. Other dynamic modes transmit HDR with metadata that can be used to reconstruct For scalable HEVC (SHVC), the A/341 standard SDR, but it requires a receiving device that calls for two spatial layers – base and understands HDR and metadata. enhancement – and the SL-HDR1 metadata may be included in either layer. The spatial A better choice is SL-HDR1, which transmits a resolution of the enhancement layer is up very good quality SDR signal with metadata to to three times that of the base layer. If the reconstruct the HDR image – and automatically SL-HDR1 metadata is in the base layer, it delivers a full HDR experience to compatible applies to both layers, but if it is present in monitors and/or set-top boxes. SL-HDR1 is the enhancement layer, it applies only to it. defined in ETSI TS 103 433-1, and was approved This gives the flexibility to the broadcaster to in early 2018 as an amendment to ATSC A/341. have different signal levels. For example, they Metadata is carried through inside the video can broadcast a free SDR base layer at lower elementary streams as SEI messages in resolution, and add a premium HDR layer at compressed streams (H.264/H.265), or carried higher resolution. Case Study: Spectrum Networks

Spectrum Networks was able to ingest both HDR and SDR feeds with a single cost-effective truck, while providing viewers with both high quality HDR and SDR content.

The viability of SL-HDR1 conversion was proven Since then, SL-HDR1 processing continues to in Summer 2017, when Spectrum Networks be used to produce live sports production. produced and broadcast a Los Angeles Dodgers It was used successfully by AT&T to deliver home baseball game in HDR for MLB Network. 4K HDR imagery of its live coverage of “MLB All SDR sources were upconverted to HDR. An Network Showcase” games. NBC Sports Group SDR downconversion was used to check the also delivered all seven home games of the SDR feed. The production generated HDR and Notre Dame Fighting Irish football team’s SDR versions simultaneously using a single 2018 season in 4K HDR for AT&T’s DirecTV production environment, distributing SDR, subscribers. The football games were produced SL-HDR1, and HDR10 (converted from SL-HDR1) on site in 1080p, and upconverted live to 4K versions to audiences. HDR. The Cobalt Solutions

Central to these productions is a workflow built For HDR output formats, the 9904 supports around Cobalt Digital’s flagship 9904-UDX-4K HLG, Sony S-LOG3, and PQ10, with 4K resolution up/down/cross converter and image processor support via 12G or quad 3G inputs. HDMI 2.0 for openGear® frames. Rather than hire output is also available with HDR InfoFrame separate trucks for HDR and SDR productions support for monitoring. It can also apply an of the same event, the 9904 can be used to arbitrary static 3D LUT to a signal for format convert SDR material to HDR (using a process conversion, color space conversion, or static called “Inverse Tone Mapping”) in real-time. ITM. The 9904 is compatible with Pomfort This way, the whole production chain can be in LiveGrade and Wowow WonderLook on-set look HDR. The processing card uses the Technicolor management software. HDR Intelligent Tone Management (ITM) software to provide this mapping function. Other Cobalt card-based products that can The Technicolor technology defines how the be part of the SL-HDR1 workflow include the available dynamic range is used, managing 9223 3G/HD/SD MPEG-4 encoder series, which brighter lights and darker shadows to deliver supports legacy 8-bit, 4:2:0 SDR devices. The sharper, more realistic images. 9992-ENC encoder supports H.264/H.265 8-bit and 10-bit applications, with resolutions up to 4Kp60.

Case Study: Spectrum Networks - Cobalt Products

Cobalt Digital Inc. designs and manufactures award-winning edge devices that help live videoCobalt production Digital Inc. and designs master and control manufactures clients transition award-winning to IP, 4K, edge HDR, devices the cloud, that and help live beyond.video production As a founding and partner master incontrol the openGear® clients transition initiative to and IP, proud 4K, HDR, member the cloud, of SMPTE, and Cobaltbeyond. also As offers a founding a best-of-breed partner in theinteroperability openGear® initiative platform and that proud simplifies member technological of SMPTE, adoption.Cobalt also Distributed offers a best-of-breedthrough a worldwide interoperability network ofplatform dealers, that system simplifies integrators, technological and otheradoption. partners, Distributed Cobalt Digitalthrough products a worldwide are backed network with of dealers,a five-year system warranty. integrators, and other partners, Cobalt Digital products are backed with a five-year warranty.