DCI Issues Memorandum Regarding Direct-View Displays

direct-view displays

The commercial-cinema industry is starting to think about direct-view displays, which are about to dramatically change what we see in movie theaters.

Commercial cinema stands on the brink of a new era. For the last 100 years, it has been based on projected images. Now, direct-view displays such as the Samsung Onyx LED Cinema Screen are poised to enter the market. These displays offer much brighter peak luminance and deeper blacks than any projection system can muster, leading to much higher dynamic range than is possible today, even in Dolby Cinemas with Dolby Vision projectors.

In recognition of this impending tectonic shift, DCI (Digital Cinema Initiatives) recently issued a memorandum regarding direct-view cinema displays. DCI is a commercial-cinema industry consortium established in 2002. The joint venture includes Disney, Fox, Paramount, Sony Pictures, Universal, and Warner Bros. Its primary purpose is to “establish and document voluntary specifications for an open architecture for digital cinema that ensures a uniform and high level of technical performance, reliability and quality control.”

The memorandum begins: “Direct view displays provide the potential for an improved high-quality image through significantly increased peak luminance and dynamic range.

“The current Digital Cinema System Specification (DCSS) and Compliance Test Plan (CTP) were crafted with projection systems in mind. With the advent of direct view displays, the associated system architecture and performance characteristics differ from projection systems such that new specifications are necessary. This document broadly defines performance and security parameters that DCI intends to define for these types of displays in order to give manufacturers guidance while a complete set of requirements is developed. Parameters defined in this memo are tentative and subject to change.

“These requirements will ensure interoperability of image content on the new generation of cinema displays while maintaining current DCSS compliant architecture.”

In other words, it’s a statement of intent to develop specifications and testing procedures for direct-view cinema displays. Some of its points are pretty vague, but it does include some specific recommendations. For example, the resolution should be at least 4096×2160 pixels—that is, cinema 4K, not consumer UHD—and the pixel structure should not be visible from a viewing distance of one screen height.

One critical difference between projection systems and direct-view displays is that the size of a projected image can vary without changing the resolution. With a direct-view display, the pixel pitch—that is, the distance between pixels—is fixed, which defines the size of a display at a given resolution. Different screen sizes will have different resolutions. To address this issue, the DCI memorandum says, “Image scaling at non-integer values may be utilized if it is clearly demonstrable that no artifacts result.” Easier said than done, to be sure, but a worthy goal.

The peak luminance should be 500 nits, while the minimum active black level—from the lowest code value that results in measurable light output from the display—should be 0.001 nit. That yields a sequential contrast ratio of 500,000:1. Also, the EOTF (electro-optical transfer function) should be 2.6 gamma for SDR content or PQ for HDR material. Interestingly, an HDR format from France called EclairColor has been proposed for use in commercial cinemas, but it doesn’t use either of these EOTFs.

The color volume should remain P3 with a D65 white point (0.3127, 0.3290), as it is in current digital cinemas. The memorandum also includes tables of target grayscale code values, chromaticity coordinates, and luminance levels. Comments on contouring, temporal artifacts, and spatio-temporal aliasing simply state that they should be minimized—duh!

I found the comments on sound considerations interesting: “Direct view displays present a unique impediment to accurate screen sound localization and dialog reproduction, potentially altering the intended sound imaging characteristics of the soundtrack. DCI recognizes that sound reproduction is an integral part of the theatrical experience. While not a display device requirement, direct view display manufacturers must develop solutions that enable the sound mix to be experienced as the filmmakers intended.” This is a vexing problem, since direct-view displays are not acoustically transparent, so you can’t put speakers behind them as you can with perforated projection screens.

The DCI memorandum is only a small first step, but an important one. It clearly indicates that the commercial-cinema industry is starting to think about direct-view displays before they are widely adopted. Hopefully, a set of standards, specifications, and testing procedures will be well defined in the near future so that the new displays perform in a consistent manner and content can be created to take advantage of their capabilities. As I’ve said before, it’s a great time to be a movie geek!

If you’d like to read the entire memorandum, click here.