In several of my past posts, I’ve referred to Wide Color Gamut (WCG) and indicated that you can’t talk about HDR without also talking about WCG. It’s time for us to discuss that in more detail. As always, this is not intended to be an in-depth discussion – just enough to give you the ammunition you need to understand WCG as it relates to TV, or to give you a launching point for your own research.

DOCUMENTING HUMAN PERCEPTION OF COLOR

Academics have been studying human vision for quite a while, and several systems have been developed to attempt to describe it in precise terms – such as the Munsell color system, which was first published in 1905 and is still in use, in an updated form, today – largely for color matching. Like many other systems, the original “Munsell Atlas Of Color” dealt with relatively few hues, which limited its widespread adoption. The most well-known of these systems today is the CIE 1931 color space, which is the incumbent color space for the film and television industries.

CIE 1931 – THE STANDARD COLOR SPACE

In 1931, the International Commission on Illumination (abbreviated to CIE from the French version of the name), created a pair of color space definitions based on a series of experiments to establish links between perceived colors and their wavelengths in the electromagnetic spectrum – specifically the responsiveness of cone cells (for a more detailed description of cone cells, see my previous post “how we see: the human visual system”). The results were then weighted and tabulated into a “tristimulus graph” of an average person – known as “the CIE Standard Observer” –and is shown in Fig. 1.

Don’t let the term “tristimulus” disturb you – there are many ways of describing light in tristimulus values: R,G,B and even Y,U,V are examples that we use every day. In the case of CIE color space, the terms used are X, Y & Z, which are derived from each of their respective curves in Fig. 1. Without going into huge detail, Y in this system is generated from the y(ƛ) color matching function and is the luminance component. X, not surprisingly, is generated from the x(ƛ) color matching function, and Z is generated from the z(ƛ) color matching function. The amplitudes of all three of these functions are always non-negative and are proportional to intensity.

You should also note that these curves are not definitive – different people will have slightly different distributions than those shown in the Standard Observer chart. In fact, the original research that ultimately produced the CIE color space only used 17 test subjects!

In order to create a graph of the CIE color space, we can now create 2 chromaticity values from these tristimulus parameters as follows:

We now have our X and Y axes for the graph, which is now the well-known “CIE horseshoe” shown in Fig. 2. Two things to note here: (1) the locus (the outside path shown as a black line) indicates the c and g coordinates for a monochromatic source as its wavelength is tuned from 400nm to 700nm, and (2) there is no line at the bottom of the graph. Anything outside of the horseshoe-shaped region is not a visible color.

STANDARD COLOR GAMUT FOR TV

We now have a model that shows the full color spectrum as perceived by the Standard Observer. Practical limitations in technology mean that we can only process and deliver a subset of that color space. In normal HDTV, the transmittable color space was defined by an International Telecommunications Union (ITU) recommendation ITU-R BT.709, more commonly known as “Rec 709”. 

The term for the legal color space is “gamut;” any color that is outside of this defined color space is termed “out of gamut.” What a system or display will do with an out of gamut signal is not defined, though in many cases, it will just result in clamping to the legal limit. Really bad things can happen with seriously out of gamut signals, though, so a great deal of effort is put into keeping signals within the legal values. Fig. 3 shows how much of the CIE space is actually legal in Rec 709.

The dot in the center of the diagram labelled D65 simply details the illuminant declared to be flat white. As you can see, there are large areas of the CIE color space that are outside the range of Rec. 709. This means that there are a significant set of colors that simply can’t be reproduced on an HDTV system. We really need to do better!

WIDE COLOR GAMUT AS IMPLEMENTED IN HDR

Now let’s take a look at the color space that is available through an HDR path. The specification here is BT-R.2020, commonly referred to as “Rec 2020” or simply as “BT.2020”. Fig. 4 shows how that relates to the CIE space.

Clearly, there are many more colors that can be reproduced. In particular the range of red and green colors is substantially increased.

This much wider range of reproduceable colors is a significant factor in the impact that HDR television brings to the presentation of video. Not only are colors more vivid, but they are also more nuanced.

Paul Turner is founder ofTurner Media Consultingand can be reached atpault@turnerconsulting.tv

Other articles in this series:

The Practical Side Of HDR

Candelas And Lumens And Nits – Oh My!!

How We See: The Human Visual System

HDR: What Is It And Why Do We Need It?

For broadcasters, video content creators, and production companies alike, there's a big change coming.

High Dynamic Range (HDR) and Wide Color Gamut (WCG) represent the next step of being “real” in the mind of the viewer with lighting that looks more natural, colors that are more saturated with vivid depth and realism.

When comparing a Standard Dynamic Range (SDR) image with HDR, the difference is staggering and you're left with a feeling that the SDR images you have been watching seem to be in a haze or fog, while HDR offers such a clear view, that it is almost a “window onto the world.”

Images come to life with detail visible in the bright specular highlights that previously would have been clipped, and smooth detail in the shadows that would have once been solid black. With WCG, colors appear more saturated with vivid depth and realism. Overall the trifecta effect of high resolution, HDR and WGC produce a visually stunning image that the latest display technologies can now provide.

With delivery to the home in this world of Netflix, Amazon Prime, YouTube and other popular video-on-demand type delivery systems, there has been a huge shift in how video content is monetized, delivered, and consumed. These over-the-top (OTT) distribution platforms have completely evolved customer expectations for content, driving greater demand for an ever-higher quality of experience.

[Read: HDR: What Is It And Why Do We Need It?]

Additionally, these systems have broken an important content delivery barrier, making it possible to not only distribute a wide range of content for different devices, like SD and HD in various resolutions (360p, 480p, 720p, 1080p), but also set a path for 4K, HDR and even 8K video content.

GET FUTURE READY

Production companies are now faced with the challenge of continuing to provide SDR, SDI, OTT, and HD formats, but also plan and provide for HDR and 4K productions—without breaking the bank.

As broadcasters and program providers work to upgrade and improve their systems and networks, and as display manufacturers continue to push the technology envelope with larger, higher-resolution displays that deliver a stunning experience, it becomes obvious that the jump to HDR content is going to be huge.

The good news is that most professional video cameras in use today have high dynamic range and that capability can be utilized with proper processing and monitoring. In fact, with the right tools in place, technology can enable broadcasters to optimize resources and prepare for HDR production now, while continuing to meet SDR and OTT requirements.

For instance, sports and live event production are developing workflows that allow 4K and HD along with SDR and HDR production to take place within one truck or studio that provides multiple outputs for distribution. Facilities that can provide these kinds of services will likely see an increase in business.

[Read: Capturing And Monitoring HDR Signals With A Waveform Monitor]

A TECH OPPORTUNITY

To develop an HDR and WCG workflow, the key is to understand that we are using the same set of digital data to create the image. However we are using these bits more efficiently by developing different curves to optimize the conversion of light from the cameras through the signal path to the displays. This involves developing a set of “Look Up Tables” that describe the curves optimized for the various Camera Log formats that capture the image. Then the conversion to SDR, or HDR using Hybrid Log Gamma (HLG) or Perceptual Quantizer is possible. Each of these different conversions varies the white point and 18 percent gray of the signal.

To manage this shift, manufacturers have integrated into waveform scopes something known as a “Stop Display,” a patented technology that provides a series of easy-to-use look-up tables that set curves where the camera video signal can be adjusted and properly converted. These adjusted stop points assure that the white point and gray point will always be at the same place, regardless of the format. The Stop Display takes the complexity of these various curves and allows the camera operator to relate them to a simple set of Stop levels.

By entering the appropriate configuration at the input stage, the conversion of the white and gray points for the SDR, HDR and Camera Log formats mean that the image being processed will always be at the same reference levels on the Stop Display, simplifying the operator’s task of monitoring the video levels. This type of log display allows operators to see the dynamic range of a camera by displaying the minimum and maximum of that range of the trace and then using parameters of the camera to adjust the levels to optimize performance for the shadows to the highlights.

The operator is no longer required to remember the various white points and that 51 percent is for PQ ST2084 and 61 percent is for S Log 3—one simply selects the camera curve being used, and then aligns the trace to the 90 percent reflectance white point and 18 percent gray that correspond within the image. The development of the Stop Display continues innovation in the development of displays that simplify the tasks of camera operators and colorists such as Diamond, Spearhead and Lightning displays that are offered on the series of waveform monitors.

The new capabilities within these types of waveform scopes can be easily added to production trucks and studios alike, extending their range of production workflow and can be extended to what future formats may be requested. With these capabilities in place, the producers and content owners can experiment with and deliver high dynamic range content to their customers.

FOLLOW THE MONEY

As with many breakthrough media technologies, the drive toward HDR content will be fueled—and often paid for—by live events. As visually impactful as any HDR content may be, live sports and live events are what will start the evolution. Outdoor sporting events have the action, natural lighting, and color dynamics that HDR and WCG can bring to life and get the audience more involved, as if they really are at the game.

Live events create shared experiences by bringing together exciting content to a sizable audience at a specific time. The live sporting event audience is not watching the big game on a smartphone. Early-adaptors and home theater owners want the larger-than-life experience by purchasing large, HDR displays and high-quality sound systems. These consumers invite their friends and family over on game day to share an experience.

Many global and national broadcasters have been experimenting with live sports/HDR content for a few years now, and we may see some major announcements this year. They have been working to iron out the process and technology, and to establish a look for their brand to establish market leadership as pioneers in this new area.

From live sports, to concerts, to other real-time events, there's no reason that regional and local production companies should not begin to leverage these new capabilities in their markets as well.

The challenge ahead is found in that the step up to HDR video production requires a new set of tools. The workflows need to be adapted to provide multiple outputs for SDR and HDR. If we're going live in a 4K HDR world, we must prepare and get our production infrastructure ready. But for production trucks, OB vans and studios, there's still the obvious need to serve the SDR content business. After all, SDR is still paying the bills—for now.

Mike Waidson is Application Engineer for Tektronix.

LAS VEGAS—“Next-generation” television is like TV with sprinkles—4K, high dynamic range, wide color gamut, high frame rate. All come with complications and possibly, trade-offs.

Ericsson’s Senior Vice President of Technology for TV & Media Matthew Goldman, video expert Mark Schubin, SMPTE President and CBS Vice President of Engineering and Advanced Technology Robert Seidel, and broadcast veteran Jim DeFilippis and will parse these advanced television features with crowd-sourced questions from their peers during the NAB Show in a Tuesday, April 19 at 2:30 p.m. Super Session entitled, “4K, UHD, HDR and More—The Future of Video.” 

Here, we have Matthew Goldman taking on the crowd:

CROWD MEMBER:What provides the best bang for the buck: 2160p resolution, high dynamic, wide color gamut, or high frame rate (120 fps)?
­MATTHEW GOLDMAN: I like to call this “the best bang for the bit.” High dynamic range is clearly the best bang for the bit (or buck) for next generation Ultra HD technology.
There are three aspects that impact this: 1) the “wow” factor of HDR is immediately noticeable by consumers, 2) many consumers’ viewing position is too far back from the display to realize the full effect of 4K spatial resolution (best viewing distance is about 1.5 picture heights back from the screen, but most consumers view the display from about 3 picture heights away), and 3) 4K spatial resolution (2160p) requires significantly more bandwidth to deliver to the consumer than HD, while HDR requires a relatively small percentage.

CM:The Canadians are now doing baseball, basketball and hockey in 4K, and distributing it via cable. What is holding up the U.S. broadcasters? What are their immediate challenges?
GOLDMAN:Likely just plain sensibility, for multichannel video programming distributors that use set-top boxes anyway (cable, satellite, telco)… it’s not possible in either country today via terrestrial broadcasting! At this early adopter stage, it comes down to priorities—who wants to lay claim to being first to generate industry buzz versus waiting for all the pieces of the puzzle to come together to offer a full-featured next-gen immersive viewing experience.

CM:What about standards? What’s needed?
GOLDMAN:Ohhh, there is just so much to do still … lots of activities are occurring across multiple standards developing organizations and industry forums. Additional HDR and wide color gamut signaling is needed on both the production side (Society of Motion Picture and Television Engineers, ITU-R) and consumer side (Consumer Technology Association, HDMI Forum) interfaces. Finalization of HDR/WCG program exchange formats (ITU-R). Recommendations for preferred interoperability points (Ultra HD Forum), system definition for delivery to consumers (ATSC, DVB, SCTE, others), streaming media (Streaming Media Alliance, DASH Forum, others). The so-called UHD-1 Phase 1 specifications really only addressed the 4K spatial resolution and in some cases, WCG signaling. Hopefully, much of the so-called UHD-1 Phase 2a specification, which will add HDR for both 2160p and 1080p, will be complete by end 2016 or early 2017. HFR is even further out.

CM:Beyond sports, what other genre will benefit and have a business ROI?
GOLDMAN:Sports and nature documentaries benefit greatly from all the new immersive viewing technologies—4K resolution, HDR, WCG and high frame rates… well, HFR if the content is high motion—not needed for talking heads! The ROI question is an interesting one because 4K resolution and HFR require extensive changes to the end-to-end workflows and a lot more bandwidth. HDR/WCG have a much smaller impact. Limited bandwidth to the consumer is a particular challenge in terms of availability and costs.

CM:Will broadcasters be “forced” into 4K/UHDTV adoption similar to the evolution of HDTV? If so, by when?
GOLDMAN: I don’t think so. It comes down to the economics, even if there will be lots of premium content driving consumer interest. Now, 1080p with HDR/WCG – “Enhanced HD” as some call it—many of us just consider this part of the next generation of UHD—that’s much more interesting as a practical business case in terms of bandwidth and ROI.
As mentioned earlier, the consumer will definitely see the benefit of HDR/WCG over conventional TV and the increase to 1080p HD resolution from conventional 1080i or 720p HD will be noticeable to consumers as well.
To be very clear, this is not about inventing a new TV format! All UHD TVs upconvert 1080p to 2160p to display as 4K, so regardless of the transmission or delivery resolution, the display is 2160p. This presents an interesting business case for broadcasters wanting to provide much of the immersiveness of next-generation UHD, but with limited bandwidth, especially when a majority of viewers are not sitting close enough to the display to see the benefits of 4K resolution (see my earlier comments about this).
Of course, there will always be marketing folks espousing the difference between upconverted 4K and “real” 4K, but again, this comes down to economics. So, if a broadcaster is able to deliver all the next gen UHD technologies—2160p, HDR, WCG, HFR—then absolutely, they should go for it. However, a lot of the benefits of the next-gen UHD can be realized with 1080p HDR/WCG if that is all one can do.

CM:What are the key dominos in the chain that need to be knocked over for the consumers to feel this is real and start spending? Is it availability of “great titles,” consumer devices, branded premium channels, marketing or something else not yet concocted?
GOLDMAN: Lots of compelling content!

CM:The young adults of today are notorious for consuming social content on small, portable devices. They are the future money for this. Why do they need it?
GOLDMAN: The benefit of these new immersive viewing technologies with portable handhelds is complicated by the nature of the use case: What is the viewing environment? If the device is used in a brightly lit area, then much of the gain is lost because the environment will mask it. However, indoor viewing on a tablet or outdoors at night will see the benefit—so is that use case enough to justify?

CM:How do we as an industry start our advancement to UHD and HDR?
GOLDMAN:It’s already in motion! Via standards and interoperability forums.

CM:What is the immediate opportunity for a TV group with regard to these technologies?
GOLDMAN: Use them to evaluate what consumers really want. The practical versus the theoretical lexicon of next-generation TV.

CM:Are we now headed toward 1080p60 with HDR and wide color as a first step, with 4K used in production and on-set display etc.?
GOLDMAN: Ahhh, please see my earlier comments! 1080p HDR/WCG—the best bang for the bit, the best bang for the buck!

CM:What are your thoughts on HDR HD facilities versus native 4K HDR?
GOLDMAN: There are many implementation of 3Gbps facilities today (support 1080p) while very little for 12 Gbps (needed for native 2160p in baseband). For all the points mentioned earlier, is it worth the investment to build a native 2160p infrastructure for the gain in user experience? This is what the broadcaster needs to grapple. This question is very different between a Hollywood studio production and live TV production or distribution.

CM:Is the notion of HDR for HD now officially dead?
GOLDMAN:Huh? It’s barely even born yet! With all of the considerations mentioned above, I believe that broadcasters will be giving 1080p HDR very serious consideration, especially since the UHD TV will upconvert to 2160p.

CM:Will 4K become a standard transmission? 
GOLDMAN:“Standard” as in common use? Maybe someday. “Standard” as in standardized format? Already in place.

CM:What are you views on affordability of transmission methods for 4K, that is, broadcast, broadband and/or satellite?
GOLDMAN:Please see my previous comments regarding bandwidth limitations and cost of infrastructure and operation.

CM:Do any of you on the panel think there is benefit to using HDR and/or 4K to author a better HDproduct that can be delivered to consumers without significant changes to current infrastructure, instead of racing to provide 4K?
GOLDMAN: Absolutely!

CM:Shooting UHD side-by-side with HD is too costly. How can we reduce the cost of producing sports in UHD and HDR?
GOLDMAN:Just like with the transition from SD to HD, there is a learning curve. The shooting style of zooms and pans in higher resolution can have negative impact on the viewer, so these need to be considered. If the shooting style can be addressed successfully, then there are known technologies for down-rez of UHD and there are discussions occurring actively within SMPTE and the ITU-R regarding mapping a larger color volume (HDR+WCG) into a smaller one, even in real-time.

CM:Do you think that high frame rate is suitable for all genres?
GOLDMAN: Only of value to high motion content, such as some sports and nature documentaries.

CM:Given the propensity of advertisers for brighter brights and whiter whites, how do we avoid the CALM Act for brightness?
GOLDMAN:Ahhh, I’ve been calling this “video loudness.” The industry definitely will need to address how to handle transitions in programs, across interstitials, etc. This work effort is just in its infancy but I believe really will be needed.

CM:How do we integrate interstitials into programming without brightness and color wars?
GOLDMAN:We need to develop “video loudness” standards!

CM:How well can we produce for both HD and HDR without serious compromises, particularly in graphics or saturated colors?
GOLDMAN:We need to develop “video loudness” standards!

CM:Given the constraints of the television, cable and satellite system, how comparable will the broadcast experience be to the ultra Blu-ray?
GOLDMAN: It can be very comparable, especially driven by compelling premium sport content. See my previous comments regarding proper viewing distance and 1080p HDR WCG.

Also see…
April 13, 2016
“Q&A: Jim DeFilippis on 4K, UHD, HDR and More”
We have many standards, but what we are missing is clarity of the problem they are supposed to solve.

April 11, 2016
“Q&A: Mark Schubin on 4K, UHD, HDR and More”
“In my opinion, HDR and HFR offer the most bang for the buck. HDR might be easier to implement, but it can increase motion artifacts, bringing us back to HFR.”