Moving images into the future

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: One reason people prefer watching films in cinemas to sitting at home with a video is that 35mm-film projectors render richer colour, closer to the range of hues that the human eye can perceive. Even today, a conventional plasma-screen television set produces only 50% of the range of colour (known technically as the gamut) that the human eye can perceive. Film, by contrast, manages around 60%. Film, however, has a fundamental problem. A pristine print of a movie has rich, vibrant colour, but every time that print is projected it is degraded, and eventually it has to be replaced.

Digital cinema projectors get around this problem, but purists complain that the gamut is not as rich as film. That may soon change, though, thanks to a new digital cinema projector that uses lasers. It has been designed by a group of researchers at the Chinese Academy of Sciences in Beijing, led by Bi Yong, in collaboration with a firm called Phoebus Vision OptoElectronics Technology, and it can produce an eye-popping 166% of the gamut of the NTSC television standard used in the United States—about 80% of the range of colours that the human eye can see.

In both the 35mm projector and the digital projector, a bright source of white light provides the illumination. This is commonly a xenon lamp, in which electricity is arced through a tube filled with the gas. In the case of a 35mm projector, the image is projected through the film and onto the screen using a series of lenses. In the case of a digital projector, the white light is first filtered into blue, green and red components and then fed into an optical-processing device that makes use of micro-electro-mechanical technology to generate the image. Hundreds of thousands of tiny mirrors are employed, each of which can be tilted into one of two positions. Each mirror corresponds to a single picture element (pixel) in the projected image and acts as a beam-steering device, controlling whether that pixel is light or dark. Intermediate shades are created by tilting the mirror backwards and forwards thousands of times a second to vary the brightness of the pixel it is projecting.