Digital Cinema Blog: Digital Cinema Technology FAQ

DCI is the abbreviation for Digital Cinema Initiatives, an organization whose owners are the six major motion picture studios (the same six studios that also comprise the MPAA). In July of 2005, DCI issued version 1.0 of its Digital Cinema System Specification, representing the consensus of DCI's members in regards to many technical details of digital cinema. The DCI specification can be thought of the cinema equivalent to the consumer specification of the Blu-ray format. Note that the DCI specification is not a standard. Standards for digital cinema are the domain of the Society of Motion Picture and Television Engineers (SMPTE). A copy of the most recent DCI specification (v1.2) can be downloaded from the DCI website. The latest version incorporates over 200 errata issued since the original release of the specification in 2005.

What does "DCI compliant" mean, and which products are DCI compliant?

"DCI compliant" is a term used to describe products that conform to the DCI specification. Products that have been tested per the DCI Compliance Test Plan (CTP) are posted at the DCI compliance web site. At the time of this writing, only DLP Cinema® Series 2 projectors have passed the CTP.

Notably, DCI compliance does not require compliance to the full set of SMPTE DCP standards. Also note that the term "DCI compliant" is not trademarked and there is no mechanism for managing its use. Anyone can claim their product is DCI compliant. The only products that are actually compliant are listed at the DCI compliance web site.

If SMPTE standards are not used for distribution today, then how is content distributed?

Products installed today meet an informal specification called "Interop." The Interop DCP (digital cinema package) is based on simplified and early standards drafts to promote interoperability in the early phase of the digital cinema rollout. Interop DCP, however, is not SMPTE DCP compliant, and does not support many of the features built-in to the SMPTE DCP. The transition from Interop DCP to SMPTE DCP recommended by the ISDCF is documented in its Timeline for Accessibility.

Are the digital cinema standards finished?

One can say that a full suite of distribution standards, and a suite of security standards, now exist. Whether or not these are complete remains to be seen. Digital cinema was developed from scratch, and many of the standards have not yet been proven. For example, SMPTE DCP, the standardized distribution format, is not in use by any studio at the time of this writing. Until this format is put to use, we won't know if the distribution standards need modification or not, or whether more standards are needed. In addition, security key management is limited in terms of standards, and more work in this area is needed if business operations are to run smoothly.

What are NATO's Digital Cinema System Requirements?

NATO's Digital Cinema System Requirements (NSR) describe the needs of the exhibition industry. Combined with the DCI specification, it provides a complete set of digital cinema requirements to guide standards committees, service providers, system providers, and manufacturers. The most recent release of the Requirements is version 2.1, online at the NATO web site.

How do I know if a product follows the latest SMPTE standards and/or NATO's Digital Cinema System Requirements?

There is no testing organization available that will tell you if a product meets all SMPTE standards, or if it meets NATO's Digital Cinema System Requirements. It is recommended that those buying equipment include detailed specifications in their equipment purchase agreements. Note that simply asking for "DCI compliance" does not guarantee that all SMPTE standards are met, and will not guarantee that NATO's Digital Cinema System Requirements are met.

For guidance in determining if current products are acceptable for studio digital distributions, Disney posts its Approved Equipment List at digitalcinema.disney.com.

How do I know if a product meets accessibility requirements?

Closed captions and accessible audio are included in the SMPTE distribution standards. They are not specified by DCI, however. As such, DCI compliance testing does not guarantee the presence or behavior of accessiblity features. To insure that these capabilities are in products you purchase, you should specify compliance to pages 2 and 3 of the Timeline for Accessibility.

Where can I learn more about the Inter-Society Digital Cinema Forum (ISDCF)?

Inter-Society is an organization chartered to socialize issues across the industry. The ISDCF is not a standards effort, nor is it a compliance or certification effort. However, it is an excellent organization for socializing the issues and solutions that appear in digital cinema. More can be learned about the Inter-Society's Digital Cinema Forum (ISDCF) at the ISDCF web site.

What is the difference between 4K and 2K projection?

"4K" is the term used to describe images that have approximately 4K vertical lines. In digital cinema, a 4K image with a 2.39:1 ("scope") aspect ratio is delivered having 4096 x 1716 pixels. A 4K image with a 1.85:1 ("flat") aspect ratio is delivered having 3996 x 2160 pixels.

"2K" is the term used to describe images that have approximately 2K vertical lines. In digital cinema, a 2K image with a 2.39:1 ("scope") aspect ratio is delivered having 2048 x 858 pixels. A 2K image with a 1.85:1 ("flat") aspect ratio is delivered having 1998 x 1080 pixels.

Do I need a 4K projection system to play a 4K movie?

No. 4K movies can be played on 2K projection systems with no modifications. Through the use of JPEG 2000 image compression technology, a 2K projection system will extract a 2K image from a 4K digital movie. Likewise, a 4K system will automatically scale the resolution of a 2K image for projection on a 4K projector. This capability results in the ability to share content between 2K and 4K systems, allowing a studio to deliver "single inventory" distributions (i.e., either 2K or 4K).

Can I use a single lens to project both scope and flat images?

According to NATO's System Requirements 2.1, yes. But some studios interpret the DCI specification as opposing the use of a single lens. A different interpretation of the DCI specification is that it prefers, but does not require, the use of separate lensing to project scope and flat images.

Can I use an anamorphic lens on my projector?

While anamorphic lenses are the best way to make efficient use of the light available to the projector, not all studios may accept their use. (See the discussion on Single Lens above.)

Note that an anamorphic lens in digital cinema does not rely on the distribution of anamorphically squeezed images, as with film. In digital cinema, the projector can electronically perform an anamorphic re-mapping of the image onto its electronic imaging device, requiring an anamorphic lens to correctly display the image. The benefit of this projection technique is that it utilizes the full imaging array, utilizing the maximum lamp power available. Images projected with an anamorphic lens can light up larger screens than in non-anamorphic installations. The anamorphic projection technique has proven useful for large screen 3-D presentations.

How are security keys (KDMs) delivered?

KDM is the acronym for Key Delivery Message. The security key for each movie is delivered in a unique KDM, one KDM per per digital cinema server. The security key is encrypted within the KDM, which means that the delivery of a KDM to the wrong server or wrong location will not work, and thus such errors cannot compromise the security of the movie.

The KDM is a small file, and is typically emailed to the exhibitor. To create the correct KDM, however, requires knowledge of the digital certificate in the projection system´s media block. See the discussion on Facility List Message below.

How are KDMs controlled?

KDMs have only a few conditions associated with their use:

§ A KDM will only work for one movie title on one server.

§ A KDM will only work within the prescribed engagement time period.

§ The server will only work if connected to a projector that is listed in the Authorized Device list of the KDM. (Not implemented at the time of this writing.)

To play a movie on two servers requires two KDMs for the movie. This means that to move a movie to a 2nd server requires a 2nd KDM. The engagement time window of the KDM is set per the business requirements of the studio distributing the movie. If your KDM expires and you don't have a new KDM to continue on the engagement, then you cannot play the movie.

To create the KDM, the public key contained in the digital security certificate for the media block must be known, as well as the public keys contained in the projector certificates. The certificates, in turn, are digitally signed by the manufacturer. While there can be many tens of thousands of digital certificates, only a small number of digital signatures must be trusted, as there are only a small number of manufacturers that make digital cinema products. In this way, those who make KDMs know that they're encrypting keys for trusted equipment.

What other conditions will cause a movie to not play?

One of the "dark screen rules" stated in the DCI specification is that equipment will fail to function when a security sub-system is tampered with. To a theatre operator, this means that the security components of your equipment must be maintained by others who are certified to repair the security components. You will have to check with the equipment manufacturer to learn who is qualified for this role.

The DCI specification also requires the playout of a movie to fail if the forensic marking capability of the server is not functioning correctly. The server's forensic marking system will mark the image and audio of the movie such that camcordered copies can be traced to the location of theft. If the marking system fails, then the server will fail to playout the movie. However, the studio can enable a flag in the security key to disable the marking system, which will also allow the movie to play with a failed marking system.

What is a Facility List Message?

The Facility List Message (FLM) is designed to carry the collection of digital certificates and related security information that exists in the secure playback equipment of a digital cinema. The FLM is sent to those who create KDMs, so that an accurate set of KDMs can be created. The FLM should be assembled by the theatre owner's equipment, digitally signed by the equipment, and transmitted by the theatre owner´s system to those entities authorized to create KDMs. This information in the FLM is also used to populate the Authorized Device List of the KDM. The diagram below illustrates the relationship of the FLM to the KDM.

Facility List and KDM

The Facility List provides digital certificate information for the creation of KDMs
(click to enlarge)

For those cases where only a single screen is to receive a KDM, such as special authorization for a sneak preview, an "partial" FLM can be created containing the security information for only the desired auditoriums. In this case, the FLM is tagged as "partial," and the purpose of the partial FLM is described in prose inside the message.

Do I need a Theatre Management System (TMS)?

A TMS provides a multiplex theatre with centralized management of all screens. As to whether or not you'll need one, the answer is both yes and no. Not everyone will need a full TMS. But everyone should have the Data and Key Management System (DKMS) component of the TMS, which can be sold independently of a full TMS. The DKMS will manage all system data, including FLMs and KDMs.

What do I need to know about digital 3-D?

Digital 3-D bears some discussion. The term "3-D" is used in digital cinema to describe stereoscopic images, where left and right images are displayed on a 2-D screen, and a method for viewing these images is employed such that each eye only sees the intended images. The result is that the left eye sees a different image from the right eye, providing the stereoscopic effect.

The distribution of digital 3-D content is intended to be single inventory, where a single distribution works for all 3-D display methods. However, this is not quite true today. The majority of Real D installations require a "ghost-busted" version of the 3-D distribution.

While there are many techniques for creating 3-D images, there are only three "add-on" technologies available for viewing them when projected by a single digital projector. The add-on technologies can be classified as those using polarized glasses, those using active "shutter" glasses, and those using spectral division glasses. See the article Choice in 3-D for an explanation of how the various 3-D add-on technologies work. Notably, all methods for projecting 3-D can display any form of digital 3-D content, regardless of how it was created.

Four questions can be asked of each method in differentiating the methods:

§ What is the cost of the glasses?

§ Do the glasses require washing?

§ Does the method require use of a silver screen?

§ How much additional cost is involved to move a 3-D movie to a 2nd or 3rd auditorium?

A fourth method for projecting 3-D images is dual-projection. Dual projection is gaining interest among exhibitors for lighting up larger screens, and the cost of the 2nd projector is not much more than the long term cost of a 3-D add-on technology.

Can a single projector display 3-D images with full (4:4:4) color representation?

No. Single projector 3-D images are displayed in 10-bit 4:2:2 color representation. While it's true that the DCI specification calls for 12-bit color with 4:4:4 color representation for 2-D images, the specification for 3-D distribution allows 4:2:2 color representation when displaying 3-D images.

However, some servers support 4:4:4 color with dual 3-D projection. Dual projectors provide more light as well. But not all studios approve of dual projectors due to the alignment issues that can occur.

What questions should I ask of digital cinema system providers?

Not all system providers approach digital cinema in the same way. Differences exist in the implementation of the Theatre Management System (TMS), which is the central control center for system in a complex. Notably, there are also differences that will affect exhibitor policies and system security. Suggested questions to ask your systems provider:

§ Moving the Movie
How long does it take to move a movie from one auditorium to another?

§ Central Office Reporting
Will the system report to your central office the arrival of content and KDMs? Will it report when KDMs are only days away from expiration? (Note that more exceptions regarding content and KDM delivery are listed in NATO's System Requirements.)

§ Maintenance
Who maintains the system? What Service Level Agreements are offered?

§ Security Log Data
The security policy in the DCI specification is "control lightly, audit tightly." A security log will likely be requested by the movie distributor. The DCI specification and SMPTE standards allows the exhibitor to remove a certain level of sensitive information from the security log. Does your system give you this ability, as well as the ability to view and approve your security logs before they're sent?

§ Security of Exhibitor Networks
The digital cinema system should not compromise the security of the theatre owner's network. The transmission of security log data to suppliers should be under the exhibitor's control. Is this how the system you are considering behaves?

§ Review NATO's Digital Cinema System Requirements
Download NATO's Requirements from NATO's web site. A lot more information resides in that document.

What work remains in digital cinema?

Digital cinema relies upon state-of-the-art information technology. It is complex, and work remains unfinished, particularly for the supply chain. Top items on the list:

§ FIPS and Obsolescene
NIST, the US body that governs the FIPS security standards that are core to the DCI Specification, frequently updates their specs. This is OK for US government entities, for whom US tax dollars are spent upgrading their equipment. But it's not OK for the worldwide cinema industry, which gets no financial support for performing these upgrades. NIST changed the FIPS 140-2 security specification in January of 2010 with a few algorithm updates and a new security key requirement that obsoletes the manner in which the KDM is used in digital cinema. Further changes will come in late 2011 as NIST obsoletes FIPS 140-2 in favor of FIPS 140-3. DCI has to decide if it wishes to let digital cinema equipment become obsolete as NIST goes along its business, and if so, who pays. The alternative is to establish an independent security standard based on the pre-2010 version of FIPS 140-2. For more technical information on the NIST changes, read our Digital Cinema Status Report in the September 2010 issue of the SMPTE Journal.

§ KDM Delivery
KDMs today are delivered primarily by email. In many cases, personal email is used. Complications arise with changes in personnel, and email delivery does not guarantee the receipts and validation required of a business process. The lowest cost to the supply chain is for KDMs to be delivered by an automated process that manages the business process and guarantees the correct delivery of keys. This is as true in 2010 as it was in 2007 when first stated on this site.

§ File Management
Content distributors need to track and confirm delivery of files, and exhibitors need to log and manage files once they are delivered. The lowest cost to the supply chain is for these processes to be handled automatically. The industry does not have a single method that allows multiple content distributors to deliver files to a theatre site and verify that their files have arrived. Similarly, theatre central office systems have no idea when digital content or KDMs have arrived, when KDMS are about to expire, or when security logs are created or sent out. Much better file management systems are needed. This is as true in 2010 as it was in 2007 when first stated on this site.

§ Digital Cinema Media Block as a Commodity
As media blocks move into projectors, they should become DCI compliant commodity items so that projector manufacturers can sell projectors with media blocks at the lowest possible price. In addition, the server hardware external to the server should be a commodity, purchased or leased as any other IT equipment. These steps will insure the lowest cost system, but the industry has yet to move in this direction.

§ Security Log Management
The exhibitor should have oversight of how security logs are handled, and be given the tools to conduct legitimate filtering of security logs as allowed by the DCI specification and the SMPTE security log standard. Much more work in this area is needed. This is as true in 2010 as it was in 2007 when first stated on this site.

What is the status of digital cinema today?

In June of 2010, 10,000 digital cinema systems were installed in the US, and approximately 22,000 systems worldwide. 66% of these were 3-D enabled. With DCIP now in full rollout, as many as 30,000 screens could be installed by the end of 2010. The graph below, courtesy of Screen Digest, depicts the worldwide rollout up to the first half of 2010.

Digital cinema worldwide installations

Digital Cinema Screens by World Region
(click to enlarge)

Technology adoption cycles have been studied for over 20 years. Stagnant sales and lack of major market uptake following a successful early adopter period is indicative of what author-consultant Geoffrey Moore calls the chasm. The diagram below shows how the progress made with digital cinema maps onto the classic technology adoption curve. Digital cinema is now expanding into the mainstream market. While it is expected that the US will be 50% converted on or before 2013, small cinema owners around the world still find it expensive to convert to digital on all screens. Further reductions in system costs will be needed as we move into the Late Majority and Late Adopter stages.

§ Digital cinema technology adoption

Digital Cinema Technology Adoption Curve
(click to enlarge)

Digital Cinema Blog

Friday, October 15, 2010

Digital Cinema Technology FAQ

What is DCI?