Patent GB-1293315-A (GB)
Title: Field-sequential colour television camera including a colour filter and one camera tube
IPC: H04N9/07
Filed: 1971-04-19
Abstract: 1293315 Colour television PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 19 April 1971 [18 April 1970] 27054/71 Heading H4F A field-sequential colour television camera, Fig. 1, comprises a variable pass-band colour filter 4 in the light path to a camera tube 1, the tube output video signal is coupled to an aperture corrector 15 and to a converter, having a memory 24 with field period delays 25, 26, for converting the field sequential tube signals to three simultaneous colour signals, the corrector 15 causing the video signal fed to the memory 24 to be restricted in frequency and the resulting frequency restricted simultaneous signals being combined (at 32, 33, 34) with high frequency signals produced by the corrector 15. Since the signals fed to memory 24 are frequency restricted (low definition) cheap, low accuracy delays 25, 26 can be used. Using a simple G, R, B, G, R, B . . . sequential segment rotating filter 4 corresponding field sequential G, R, B signals pass to aperture corrector 15. The progress through the corrector of a transition 15 in the video signal, corresponding to an image edge or detail, is shown, delay γ 1 being a fraction of a line period 100-140 ns. and 18 and 19 being by-two dividers. The output of subtractor 21, i.e. ¢ (15 1  + 15 3 ) - 15 2 , is a high frequency cycle aperture correction signal C, and is subtracted from the γ 1  delayed transition signal 152 to give a reduced (low definition) frequency video signal D. The colour signals G, R, B, when so converted to low definition are designated by dashes, i.e. G<SP>1</SP>, R<SP>1</SP>, B<SP>1</SP>. The memory 24 gives outputs J, K, L, which are connected to respective commutator switches 28, 29, 30 switching at frame frequency to give simultaneous signals by combining switch outputs 28 3 , 29 1 , 30 2  (G<SP>1</SP>), 28 2 , 29 3 , 30 1  (R<SP>1</SP>) and 28 1 , 29 2 , 303 (B<SP>1</SP>). Omitting signal corrector 31, these combined outputs can be fed to the high frequency restoring adders 32, 33, 34. In the case of saturated colours or large single colour areas, this simple system gives a fluttering picture. If for example green G predominates, the corrector 31 must then be used to subtract green from all the switch signals and each filter segment is split in two, one half being green (i.e. the filter is G, G, B, G, R, G). In the case of saturated colours, for which the particularly shown corrector 31 is used, the filter may be as shown in Fig. 2, transparent (luminosity Y) half segments alternating with reduced definition (reticulated) red and green half segments #R and #G and opaque half segments. When the segment Y + #R is in front of the camera tube for example the high definition signals are derived from the luminance half segments and the low definition signals are derived from the R half segment. The only aperture corrector signal is from the luminance segments, i.e. Cy and the only converted low definition signal is Y1 = Y - Cy. Appearing at outputs W, X and Y are simultaneous flickerless signals G + Cy, #R + Cy and #B + (Y1 - Y) + Cy respectively. The frequency characteristics of Y<SP>1</SP> (produced electronically) and Y (produced optically), are different (Fig. 4, not shown). The filter of Fig. 3 (not shown) and by-two dividers q 1 , q 2 , then lead towards equalizing these characteristics.