In a flying spot scanner (FSS) or cathode-ray tube (CRT) telecine, a pixel-sized light beam is projected through exposed and developed motion picture film (either negative or positive) and collected by a special type of photo-electric cell known as a photomultiplier which converts the light into an electrical signal. The beam of light "scans" across the film image from left to right to record the horizontal frame information. Vertical scanning of the frame is then accomplished by moving the film past the CRT beam. In a colour telecine the light from the CRT passes through the film and is separated by dichroic mirrors and filters into red, green and blue bands. Photomultiplier tubes or avalanche photodiodes convert the light into separate red, green and blue electrical signals for further electronic processing. This can be accomplished in "real time", 24 frames per second (or in some cases faster). Rank Precision-Cintel introduced the "Mark" series of FSS telecines. During this time advances were also made in CRTs, with increased light output producing a better signal-to-noise ratio and so allowing negative film to be used.