The Digital Cinema Initiative (DCI) group has started working on specifications for High Dynamic Range video in cinema, in part to prepare for the arrival of large-size LED cinema displays (via Display Daily).
HDR cinema specification
The Digital Cinema Initiative (DCI) – backed by Disney, Fox, Paramount, Sony, Universal, Warner Bros, and other – was formed based on projector systems. The movie projector is literally what made possible the concept of cinema and it has been in use for over a century. However, modern projectors have limitations in areas such as brightness and dynamic range.
A new type of large-size “direct view displays” – or LED displays – are emerging for cinema. Samsung and Sony have both proposed using large LED screens to replace the projector system in cinema, and Samsung has even started installing it in a few places. The DCI group is preparing for the big leap.
- “Direct view displays provide the potential for an improved high-quality image through significantly increased peak luminance and dynamic range,” the DCI group wrote in a memorandum. “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.”
As you may know, Dolby is already claiming HDR in Dolby Cinema but some industry members have started referring to the projection system used by Dolby as “EDR” (Enhanced Dynamic Range) rather than HDR (High Dynamic Range).
The DCI group has released a draft for a HDR cinema system specification and a compliance program. Notably, the proposed cinema specification includes many of the same aspects that consumers are already enjoying on HDR TVs in the living room. At this point in time, they invite industry members to give feedback.
500 nits brightness, changes to scaling
First of all, the DCI group proposes using the PQ (Perceptual Quantizer) curve for 12-bit HDR video in the cinema. PQ already forms the basis of the HDR10, HDR10+, and Dolby Vision formats, so it would make it easier for studios to master movies for cinema and the living room.
Furthermore, they are proposing 500 nits peak brightness and 0.001 nits black level for cinema HDR. This is virtually impossible on a projector and is of course motivated by what self-emitting display technologies such as OLED and microLED/LED can do. They also propose to keep using the DCI-P3 color space rather than the larger BT.2020 color space – at least for now.
The resolution must be “at least 4096 (4K) horizontal and 2160 vertical pixels” but the DCI group is considering allowing a significant change in this area; scaling. To date, scaling has been prohibited. They note that “image scaling at non-integer values may be utilized if it is clearly demonstrable that no artifacts result”.
Today, it is easy to make the picture larger or smaller with a projector and lens calibration. However, an LED display has a fixed resolution at a given size. It cannot be expanded after installation without image resolution changing. This is quite inflexible compared to what exhibitors have been used to and the DCI group clearly acknowledges this challenge.
Furthermore, the memorandum had something to say on the subject of speakers. Today, the center channel is placed behind the canvas but this will no longer be feasible when moving to large-size LED displays.
- “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.”
While cinema has traditionally led innovation in picture and audio technologies – that have later trickled down to consumer displays – the industry is falling behind in the transition to HDR video that that is well underway in the home entertainment space. This is the first important step towards formulating specifications for HDR cinema but it will likely take some time before it can be finalized.