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Wirephoto Standards Converter

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3 Author(s)
D. Troxel ; Massachusetts Institute of Technology, Cambridge, MA ; W. Schreiber ; C. Seitz

A standards converter that translates simultaneously between the United States and European wirephoto networks has been developed. Items of noncompatibility include picture duration, lines per minute, lines per inch, and scanning direction. The system operates completely automatically. It discriminates between voice and picture signals, adjusts for input level, and determines the input line scanning frequency. After appropriate analog processing, the signal is digitized and passed through a magnetic core storage onto a magnetic drum, which has sufficient capacity to accommodate the 6-minute difference in picture duration. The data are later read from the drum into the core, put into the correct time scale, converted back to analog form, and used to modulate the output carrier. Since the United States picture has more lines than the European, a line interpolation process is used in the United States-to-Europe direction that converts 13 lines of the input picture into 12 lines of the output picture. In the reverse direction the picture is shrunk in the horizontal direction by one part in 13. Since its installation in January, 1968, the converter has been operating continuously in New York City. Its inputs are normally left connected to the appropriate networks, with the picture editor making the decision in each case about whether the output is to be transmitted, recorded on tape for later use, or abandoned. Considerable savings in time and improvement in quality have resulted, as compared with the previous procedure of rescanning a picture on one machine which was recorded on another.

Published in:

IEEE Transactions on Communication Technology  (Volume:17 ,  Issue: 5 )