automatic algorithms to identify fuzzy or complex region boundaries, such as those between a subject's hair and face. Colorization of moving images also requires motion compensation, tracking regions as movement occurs from one frame to the next. Several companies claim to have produced automatic region-tracking algorithms: Legend Films describes their core technology as pattern recognition and background compositing that 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 foreground areas are colorized, background masks are applied frame-to-frame. Timebrush describes a process based on neural net technology that produces saturated and crisp colors with clear lines and no apparent spill-over. The process is cost effective because it relies on computers rather than human effort, and is equally suitable for low-budget colorization and broadcast-quality or theatrical projection. A team at the Hebrew University of Jerusalem's Benin School of Computer Science and Engineering describe their method as an interactive process that does not require precise manual region detection, nor accurate tracking; it is based on the premise that adjacent pixels in space and time that have similar gray levels should also have similar colors. At the University of Minnesota, a color propagation method was developed that uses geodesic distance. A highly labor-intensive process employed by the UK-based film and video colorization artist Stuart Humphryes, in conjunction with video restoration company SVS Resources, was employed by the BBC in 2013 for the commercial release of two Doctor Who serials: the first episode of The Mind of Evil and newly discovered black and white footage in the director's cut of Terror of the Zygons. For these projects, approximately 7,000 key-frames (approximately every 5th PAL video frame) were fully colorized by hand, without the use of masks, layers, or the segmentation method. These were then utilized by SVS Resources to interpolate the color across the intervening surrounding frames using a part computerized/part manual process. British photo colorizer Tom Marshall has digitally colorized various historical subject matters including slavery, the Holocaust, the First World War, Victorian London, and the Suffrage movement. Uses of colorization Partial colorization The earliest form of colorization introduced limited color into a black-and-white film using dyes, as a visual effect. The earliest Edison films, most notably the Annabelle Serpentine