GB1342561A - Methods of and apparatus for transmitting by television infor mation added to an original document - Google Patents

Abstract

1342561 Composite picture reproduction GRUNDIG EMV 30 March 1972 [1 April 1971] 15090/72 Addition to 1286766 Heading H4F In apparatus for displaying marks superimposed on a background, as described in Specification 1,286,766 and comprising an image of the background 1, Fig. 1, covered by a first polarizing filter 3 upon which the marks are made and a second, relatively crossed polarizing filter 7, such that a TV camera cannot see the background and produces video signals representing the marks only, the transmission band width required for the video signals is reduced by sampling the video signal A, Fig. 2, by fast gating pulses B from clock 12 and producing a pulse D when the sampled valve is above a threshold 25, C. Pulses D are converted to binary full-width pulses E in expander 14 and stored in this form at 15. Transmission of the stored binary video is carried out at a slow, small band width, rate, using slow clock 16. The received video is stored at receiver store 18 and is sampled at a fast rate for use in C.R.T. projector 20 and projection of the mark image on background 1<SP>1</SP>. Several different marks can be simultaneously stored in respective stores for selective projection.