Patent GB-1351083-A (GB)
Title: Colour television camera including a raster position corrector
IPC: H04N9/093
Filed: 1972-05-03
Abstract: 1351083 Colour television camera PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 3 May 1972 [6 May 1971] 20573/72 Heading H4F To correct registration errors in a colour television camera in the horizontal and/or vertical directions, changes in the output signals from two of the pickup tubes (e.g., the red and blue pickup tubes 3R and 3B) are each compared with changes from the third pickup tube (e.g. the green pickup tube 3R) and the resulting comparison used to control the scanning of the respective red or blue pickup tube. The red and blue beams of a camera using only one pickup tube employing three scanning rasters may be similarly corrected. In a first embodiment, Fig. 1, the green video signal G 0  is multiplied 20R with the red video signal R 1  delayed 14R by a period T and the difference between the resulting signal P 1  and a signal P 2  derived by multiplying the delayed red signal R 1  with the twice (2T) delayed 15, 16 green video signal G2 is integrated 24, 25, the integrator having a time constant at least of the order of one field period (preferably approximately five field periods in an interlaced television system for correction in either the horizontal or vertical direction). For horizontal correction T is equal to one picture element period and for vertical correction T is equal to one line period. The integrated error signal PR is applied to a store 26R which preferably includes a threshold device, and this error signal when it exceeds the threshold is fed to level control 27R for horizonal correction which applies a direct current to the horizontal deflection coil 5R, or to level control 28R for vertical correction which applies a direct control voltage to adjust the D.C. level of the sawtooth field deflection current in deflection coil 6R. Delays 14R and 14B may be omitted if it is arranged that the pickup tubes 3R and 3B themselves provide signals which are delayed relative to the tube 3G. Delays 15 and 16 form part of an aperture corrector 12, the resulting aperture correction signal G 1  - (G 0  + G 2 )/ 2  being fed to adders 13 for the three colour video signals. Both horizontal and vertical registration correction may be effected simultaneously (Fig. 4, not shown) the signal G 1  (delayed by one line period) from a vertical aperture corrector being applied as the input of a horizontal aperture corrector, the output from which is applied to the adders 13 together with the output from the vertical aperture corrector delayed by a further picture element period. In this embodiment the registration correction error signals for the red and blue tubes are derived sequentially and stored for simultaneous use, the horizontal error signals being sequentially derived and then the vertical error signals, each being derived over for example ten field periods during the central region of the rasters. Instead of using two multipliers 20R and 21R followed by a subtractor 22R, subtraction of G 2  from G 0  may first be effected followed by multiplication by R 1  i.e. only one multiplier instead of two is required.