Scanning

The scanner is a device that translates an image from previously exposed film into a digital format. Current devices use a CRT or laser to scan a film frame on a point-to-point basis or use a charge-coupled device (CCD) to digitize the frame by area or line by line.

The CRT or laser is the moving spot illumination source that scans the image at a constant intensity. Controlling the beam diameter can determine the size of the pixels and thus the resolution of the scanned image. As the beam scans the film frame pixel by pixel, light gathered by an optical system passes through diehroic filters and splits into red, green and blue components. The intensity of the light hitting R, G & B light sensors converts to an analog electrical signal. An analog to digital converter translates the analog signal into a digital value for each color.

CCD scanners utilize a technology employed in professional video cameras. Instead of a scanning light source, the CCD scanner uses an incandescent or xenon light source similar to the optical printer. The number of pixel elements in the CCD array determines the resolution of the scanned image. Grid arrays of 2,000 pixels by 2,000 lines or 4,000 pixels by 4,000 lines enable scanning an entire frame while holding the film on fixed registration pins. Line arrays of 2,000 to 4,000 pixels require that the film be rolled past the CCD to scan the entire film frame.

The computer captures the number stream produced by the scanner and creates a pixel array database in a format compatible with the database of a simulated image. The time required to scan a frame varies from under five seconds to several minutes depending on the device and the resolution.

The computer can composite both foreground and background elements in what might be called digital film printing. Although the computer can use any color to ex tract a matte, it is most practical to use a spectrally pure color such as Ultimatte blue or green. However, it is not necessary to have a blue- or green-screen exposure limited to one color record of the film as is needed in film-based matting systems. The same qualification applies, however, in that the background screen color cannot be in the foreground subject.

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