What Is a Digital Movie Projector?

A digital movie projector is a device that performs the same function as a film-based motion picture projector, but uses digital data and a different projection scheme. There are two primary types of digital movie projector. The first is called a micromirror projector and uses millions of tiny mirrors on hinges to control how the images are displayed on the theater screen. The second is called a liquid crystal display (LCD) projector. An LCD projector uses a large mirror with an LCD sheet over top of it to adjust how the light is reflected onto the screen.

One reason a digital movie projector is necessary to show a motion picture that was filmed digitally is because the information used to form the images is stored as numbers. Instead of being able to shine a light through a strip of film, the image data needs to be decompressed, translated and then somehow projected onto the theater screen. Without a complex mechanism that uses computerized display techniques and fast video processing, showing a digital movie in a theater might not be possible.

A micromirror digital movie projector begins with a very bright light source that is directed through a prism. The prism breaks the single beam of light into its component color parts. Each of the individual color beams hits a semiconductor plate lined with millions of mirrors, each of them microscopic in size and balanced on a type of hinge. The mirrored semiconductor plate is called a digital micromirror device (DMD).

The DMD is fed information from the digital movie. Each of the micromirrors can have its reflective face fully exposed, fully hidden or spun at some rate. As the colored light hits the mirror, depending on the mirror's position, the color is either projected at full power, not at all, or as a gradient of itself. Each mirror is related to a tiny, nearly undetectable dot on the projection screen. The mirrors are flipped thousands of times every second while the movie is playing to create the image seen.

An LCD projector, also sometimes called a digital image light amplification (D-ILA) projector, uses a slightly different technique to achieve nearly the same results. A strong light is aimed at a mirror that has been coated in a special liquid crystal display sheet. As information from the digital movie is fed to the LCD sheet, it reacts by allowing all, none or some of the light to pass through and be reflected off the mirror. By variably polarizing the pixels of the LCD sheet, like the micromirrors, the light is manipulated into forming an image on the projection screen.