[The question is being answered by David Reisner of D-Cinema Consulting. David is a board member of several organizations such as the ASC and ISDCF, co-author of several books on many fields of the cinema process and specializes in design and implementation of digital cinema infrastructure projects.]
For nearly 100 years, motion pictures have been delivered to theaters on 35mm film and have been shown with film projectors.
Digital Cinema, officially called D-Cinema in the technical community, delivers movies to theaters as digital files – most often on harddisk, sometimes via satellite, probably in future also by network/internet. The movies are then shown using digital cinema servers (special purpose computer systems) and theater-grade digital projectors. D-Cinema also includes/requires a number of digital and physical security mechanisms, to keep content (movies) safe. The key documents are the DCI “Specification” (actually a requirements document) and a number of SMPTE standards.
D-Cinema requires support for 2048 x 1080 or 4096 x 2160 images and 14 foot-lambert brightness (similar to film standard brightness, although theaters sometimes use lower light levels for cost). Movies are distributed in 12-bit X’Y’Z’ color – much more color detail than HDTV’s Rec. 709. X’Y’Z’ can represent all the colors that a human can see, but the real limitation is the projector (and, to be fair, the camera and post-production process). All D-Cinema projectors show at least a minimum color gamut which is a significantly wider range of color than Rec. 709 – similar to the range supported by film.
For some markets or purposes (e.g. pre-show, advertising, maybe small markets), some people use things informally called electronic cinema, e-cinema. There is no formal standard for e-cinema although there is some informal agreement in certain areas. E-cinema will have lower resolution, narrower color, less brightness, and little or no security.
Major studio content will only be distributed to D-Cinema systems that meet the SMPTE and DCI specifications and requirements, and have passed the DCI Compliance Test.