Video synthesizers are characterized by the ability to generate forms from electronic elements without recourse to the external information ordinarily provided by a camera. In the 1970s, synthesizers were integrated into studios equipped with cameras for reworking the image, a control panel, and a tape deck. An early version that has remained famous to this day is Eric Siegel's PCS (Processing Chrominance Synthesizer), designed in 1968; it is a "colorer" that operates with a black-and-white signal, creating colors in function of different densities of gray. In 1970 Siegel invented the EVS (Electronic Video Synthesizer), which, in addition to color, generated abstract forms. Steina and Woody Vasulka were among the users of Siegel's synthesizers. Also in 1970, Stephen Beck perfected his Direct Video Synthesizer, a tool for composing images. Around the same time (1969-1970), Nam June Paik, who was artist-in-residence at WGBH-TV in Boston, collaborated with engineer Shuya Aba to develop a synthesizer that created its own images. Two of the most well-known synthesizers of the early 1970s were Bill Etra's scan processor, a device that operated directly on the screen's scan lines, and the IVS (Intelligent Video System). Etra and Steve Rutt designed the RE (Rutt-Etra) synthesizer that operated on manipulations of the received image and allowed two images to be reworked simultaneously, with results that were close to computer animation. In Europe at this time, R. Monkhouse in England created the Spectron and Marcel Dupouy in France, the Movicolor (1972-1974). These two synthesizers not only serve to color existing images but can generate images themselves. Unlike their counterparts in the United States, European builders were not artist technicians but electronical engineers. France also had Coupigny's "truqueur universel" (universal special effects), which allowed images to be manipulated and colored.