The digitization of signals has evolved over time. Digital signals, which inherently require more bandwidth than their analog counterparts that they are intended to replace, generally require digital compression to fit the signal into available bandwidth. Digital signals allow low bandwidth metadata to accompany it, metadata fulfilling the role of “data about the data,” which can be a benefit in terms of identifying the data, its origin, and its purpose. But as the signal becomes more complex, a “data that is not metadata” has emerged, where the presence of this “signal data” is required to properly render it. At its simplest, such data could instruct a projector to frame a particular aspect ratio. A more complex application would be to instruct a projector to use a particular color space profile with a certain scene. A more familiar and real application is to instruct a sound rendering engine that a particular sound object is to be heard from a particular position in the room while having a certain size. With the exception of immersive sound, digital cinema has steered away from such signal data. But that may change if the potential for such innovation can reduce the inventory of distribution versions. The challenge is whether this direction would alter the ability of cinema to be the ultimate format for experiencing creative intent.
The trend for active signal data can be seen in the evolution of equipment and workflows. Decisions that once were permanently made in camera can now be recorded as data and handed off to downstream workflows where final decisions can be made. Sound mixes once irresolutely fixed in the studio are now performed in the auditorium using data recorded by the sound mixer. In each of these cases, decisions once made upstream are now made downstream. The natural trend of digital signals is to make decisions as far downstream as possible.
The challenge is to maintain creative intent when making decisions downstream. Creative intent is managed in immersive sound, for example, by responsible technology providers that exert a fair degree of control over their ecosystem. But what happens when no one is able to exert such control? Specifications and standards only go so far towards insuring interoperability. To insure a certain degree of quality in the experience of the rendered signal, more attention is needed.
The problem is rising in the area of consumer high dynamic range (HDR) displays, where not only may color primaries, and thus color space, vary from display to display, but peak white level could also vary significantly, imparting further impact on color volume. If display color space and peak white levels are in excess of those used when mastering the content, then no colors should be outside the display boundaries and one would expect predictable results.
But there is always the director willing to push the envelope, and that’s where things can get edgy. The UHD Alliance released specifications in January that boggle the minds of colorists. Quoting from the press release, a UHD display could have “more than 1000 nits peak brightness and less than 0.05 nits black level, OR more than 540 nits peak brightness and less than 0.0005 nits black level.” In the first case, the dynamic range, in nits, is 20,000:1. In the second case, the dynamic range is 1,080,000:1. If you’re a colorist, which one do you master for? If mastering for 1,080,000:1, what will this look like on a 20,000:1 display? The politicians of the specification world will say this problem can be solved with signal data that instructs different display types as to how to properly render. Such talk eases agreement on a specification that must encompass wide variations in display technology. But it leaves open the question of who will insure that the consumer experiences what the colorist intended.
That may not sound like a serious question for consumers, who enjoy tweaking the knobs on their displays with little or no concern for creative intent. But that’s not true of cinema, where the presentation of creative intent is a core value. Today, there is no such thing as widely available HDR in cinema. But it would be unwise to think that the current limitations in technology won’t change. New technologies that are managed within a closed ecosystem, such as Dolby Cinema or IMAX, will not be the problem. The problem will manifest as new technology wends its way into mainstream cinema, without an adequate means to define and assert the audience experience. The politicians will defer to signal data as the solution. But we’re going to need to be a lot smarter if we’re going to preserve creative intent in cinema.
