<P> To perform digital colorization, a digitized copy of the best monochrome film print available is needed . Technicians, with the aid of computer software, associate a range of gray levels to each object, and indicate to the computer any movement of the objects within a shot . The software also is capable of sensing variations in the light level from frame to frame and correcting it if necessary . The technician selects a color for each object based on (1) common "memory" colors such as blue sky, white clouds, flesh tones and green grass, and (2) based on any known information about the movie . For example, if there are color publicity photos or props from the movie available to examine, authentic colors may be applied . (3) In the absence of any better information, the technician chooses a color that fits the gray level and that the technician feels is consistent with what a director might have chosen for the scene . The computer software then associates a variation of the basic color with each gray level in the object, while keeping intensity levels the same as in the monochrome original . The software then follows each object from frame to frame, applying the same color until the object leaves the frame . As new objects come into the frame, the technician must associate colors to each new object in the same way as described above . This technique was patented in 1991 . </P> <P> A major difficulty with this process is its labor - intensiveness . For example, in order to colorize a still image an artist typically begins by dividing the image into regions, and then assigning a color to each region . This approach, also known as the segmentation method, is time consuming, as the process of dividing the picture into correct segments is painstaking . This problem occurs mainly because there have been no fully automatic algorithms to identify fuzzy or complex region boundaries, such as between a subject's hair and face . Colorization of moving images also requires tracking regions as movement occurs from one frame to the next (motion compensation). There are several companies which claim to have produced automatic region - tracking algorithms . </P> <P> Legend Films describes their core technology as pattern recognition and background compositing which moves and morphs foreground and background masks from frame to frame . In the process, backgrounds are colorized separately in a single composite frame which functions as a visual database of a cut, and includes all offset data on each camera movement . Once the foregrounds are colorized the background masks are applied frame to frame in a utility process . </P> <P> Timebrush describes a process based on neural net technology which produces saturated and crisp colors with clear lines and no apparent spill - over . It is claimed that the process is cost effective and equally suitable for low - budget colorization, as well as for prime time broadcast - quality or theatrical projection . </P>

How do they turn black and white to color