Digital Cinema Packages: DCI and DCPs (part I)

DCI, DCP, KDM, etc… are “words” that are being incorporated into our industry and that little by little we are going to have to master. But, what is DCI, what are DCPs, we are going to try to shed some light on these issues, as well as show you some tools to generate DCPs.

To start at the beginning, DCI stands for Digital Cinema Initiatives, an association of the major American movie studios, created to set the guidelines for the distribution and exhibition of digital cinema.

This association established technical parameters to be able to generate, distribute and exhibit films in digital format. The premises for the regulation were to guarantee the maximum anti-copy security of the contents and a level of quality that would guarantee the exhibition today and in the future; given that the new masters of the films were going to become digital files.

The original regulation dates back to 2005, and has since undergone two revisions in 2007 and 2008, as well as an appendix on stereoscopic cinema in 2007.

Well, enough of the story, how does all this affect me? The main implication is that these studios have such commercial power that they have made this standard the “de facto” standard for digital cinema in the industry. Shortly after the publication of the standard, the first DCI-compliant projectors and servers began to be introduced, until it became the standard for distributing and projecting digital cinema. So, if you create any content and want to be able to project it in a movie theater, you have to comply with this standard…

And at this point, can’t I generate a “DCP file” directly with my editing, finishing or mastering software? Well, in most of the cases, no, in most cases not. Let’s see what are the specifications set by DCI and why it is not so easy to generate these contents; there will be some inaccuracies to simplify and make some concepts more understandable.

The DSM (Digital Source Master) is the first step, it is nothing more than the original material generated by our finishing or mastering system, this material must undergo a series of conversions in order to create a valid DCP, and these correspond to a series of phases described by the DCI standard.

The DCDM (Digital Content Distribution Master) is the next step, it is to convert the material to 2K or 4K resolutions marked by DCI and convert it to TIFFs in XYZ color space at 16 bits (although nowadays only 12 bits are used) and with a gamma of 2.6.

Regarding 2K or 4K resolutions, DCI is very restrictive, since it imposes very rigid preset resolutions. Originally the DCI standard established only two frame sizes, 2048×1080 pixels for 2K and 4096×2160 pixels for 4K, both at 24 fps. Subsequent revisions to the standard no longer made it necessary to add black bands to comply with more standard film formats such as Scope (2.39:1) or the 1.85:1 standard.

Thus, as of today, these are the resolutions supported by DCI:

In 2K, 2048×1080 pix* is kept as the base, and 2048×858 pix are added for Scope, and 1998×1080 pix for 1.85

In 4K, the base is 4096×2160 pix, as well as 4096×1716 for Scope and 3996×2160 pix for 1.85.

Finally, a 2048×1080 pix format at 48 fps is added for stereoscopic 3D, with 24 frames for each eye, which are sent to the projector alternately, so that the system in the cinema can then adapt the content to each of the existing stereoscopic projection systems.

This DCDM must already take into account another feature of DCPs, they use a somewhat special color space, the XYZ. This color space was developed in 1931 by the CIE, and is supposed to be the one that most faithfully reflects the colors visible to the human eye. Each color is represented as a combination of values on the X,Y,Z axes and this color space is often used as a basis for calculating other color spaces (such as RGB or sRGB common in computers).

* pix is used as an abbreviation for Pixels
** Images courtesy of DVS