Using wavelets for compression eliminates some of the glitches that appear in images when important data is ignored. However, the process takes a lot of computing power. That’s probably why it hasn’t made it into popular consumer products, but it’s not an insurmountable problem for high-end theater systems.

JPEG2000 also assigns more bits to the digital representation of color, another means of improving the image. Today’s digital cameras typically allocate 8 bits per color, or 24 bits per pixel, to identify the color of that pixel. JPEG2000 allocates 16 bits per color, or 48 bits per pixel, creating a much broader color palette. The result of wavelet compression, combined with more accurate color representation, is a typical file size for a feature movie after JPEG2000 compression of 300 gigabytes or less.

The industry group spent much less time considering standards for sound. They determined that, because the bandwidth for sound is negligible as a percentage of a movie’s total bandwidth, they could simply use standard uncompressed CD-quality audio as represented by the Wave digital encoding format. This audio file format, developed by Microsoft, is common in PCs and game software.

Having settled on the type of data movie studios would send to exhibitors, the next challenge was to figure out what kind of equipment would translate those bits into images on the big screen.

With film, exhibitors have a mature, stable technology that requires little training to use and is reasonably easy to fix when equipment breaks down. Consequently, problems in film projection are rare, and it’s unusual that they interrupt more than a single showing. To measure up, digital cinema systems had to have similar reliability, ease of use, and limited downtime.

At a minimum, a digital cinema system requires a digital projector and a media player. The media player stores the movie and decrypts and then uncompresses the digital cinema files during playback. The system also needs to have user-programmable functions, so that exhibitors can easily select which trailers, advertisements, and movie files to play. Another thing: it can’t let pirates get at the data.

The projector has to be able to take the output of the media player and turn it into the picture that the moviemaker intended. That is, the projector needs to know if the picture is in CinemaScope, which is an extended wide-screen format, or in a squarer format. It also needs to know if the movie is to be presented in 3-D or not [see sidebar, “Digital Cinema: Another Dimension”]. And it has to add forensic data that, though invisible to the moviegoer, will disclose the time and place of the movie’s showing if a video-camera-wielding pirate captures the images.

That’s the minimum. But in today’s world, a single-screen ­theater is rare. In modern multiplexes, exhibitors play movies on multiple screens and move them from auditorium to auditorium while trying to match seating counts to demand. To operate in a multiplex, the digital cinema media players must be networked with a central management server [see diagram, “Following the Bits”]. This networked system allows exhibitors to move titles between screens within the multiplex and enables third-party support companies to remotely monitor and troubleshoot the system.

After Digital Cinema Initiatives released the first digital cinema specifications in the summer of 2005, a few companies began marketing tools to equip multiplexes. Access Integrated Technologies, Dolby Laboratories, Doremi Labs, Eastman Kodak, NEC, and QuVIS, which had each already started manufacturing digital cinema equipment, introduced upgrades to comply with the new specification.

All systems included provisions for networked control and management of the screens, to allow theater managers to schedule movies and to start and stop shows in one auditorium from any other auditorium in the complex. All but the NEC systems, however, lacked a central library server to allow flexible programming of movies into any of multiple auditoriums. And all would work only if a theater complex installed the same brand of equipment for every screen.

In late 2005, two companies—Christie Digital Systems, in Cypress, Calif., and Access Integrated Technologies, in Morristown, N.J.—jointly developed a central library management system. So far, this is the only system designed to allow theater owners to purchase media players and projectors from multiple manufacturers.

Christie or AccessIT can build the library server on Windows or Linux-based servers from Compaq, Dell, and Stratus. Media players might come from Dolby, Doremi, Kodak, or QuVIS. The ability to choose adds flexibility and competition that lowers prices. All four players can use the same digital files, removing the biggest headache for the movie studios.

Throughout the development of digital cinema, the industry has been paying a lot of attention to the digital cinema projector. The projector is central to the whole system and has the biggest effect on picture quality. Today’s typical projector uses DLP chips, a technology also used in high-end home projection TVs. DLP chips modulate light by bouncing it off arrays of micromirrors, one array each for the red, green, and blue components of a video picture [see “Goodbye, CRT,” IEEE Spectrum, November].

TI’s DLP Cinema, designed for the commercial market, uses 2 million micromirrors on each chip to produce 2048 lines of horizontal resolution. Home sets typically contain 1 million mirrors and project 1280 lines of resolution; they have less contrast than the cinema-grade chips.

The 2 million–mirror, 2048-line theater system is the pixel equivalent of what the eye can see in 35-mm celluloid film projected from a pristine print by a well-maintained film projector, as verified by ordinary viewers as well as Hollywood’s “golden eyes.” A small number of theaters across the globe have successfully used DLP Cinema for five years without significant problems, proving the reliability of the technology.

Now developing even higher-resolution, 4096-line (4K) projectors, JVC, NTT, and Sony are using liquid crystal on silicon (LCOS) technology, which is also in sets sold for home use. LCOS devices use digital memory cells in a densely packed array. The memory cells cause the liquid crystals to twist and, like a window blind, change the amount of light reflected, from pure white to black. LCOS devices are undeniably promising but still untested in the commercial cinema market.

The two projection technologies also differ in their ability to display 3-D movies. In this area, DLP has the advantage. Current LCOS systems cannot display 3-D very well because of the higher frame rates required, removing one of the advantages digital cinema has over film.