Patent GB-1245533-A (GB)
Title: Colour video signal generating apparatus
IPC: H04N9/083
Filed: 1969-02-05
Abstract: 1,245,533. Television. SONY CORP. 5 Feb., 1969 [5 Feb., 1968], No. 6215/69. Heading H4F. Image light is focused on a photo-electric conversion layer 3, Fig. 1, of an image pick-up tube 4 e.g. a vidicon tube, by an objective lens 2 and via a plurality of striped colour filters 7 of different wavelength band characteristics disposed at different distances from a lens screen 8 comprising a plurality of cylindrical lenses. The pitches of the stripes of the colour filters and the cylindrical lenses of the lens screen 8 are selected to have specific relationships to each other, and the optical distance between the lens screen 8 and the photoconductive layer 3 and that between the lens screen 8 and each of the striped filters are selected in a specific relationship to each other. In a first embodiment the colour filters 7 comprise filters 7Y, 7C and 7M, Fig. 2 of pitch A having vertical yellow, cyan and magenta stripes respectively spaced by transparent portions. Lens screen 8 comprises alternate cylindrical lenses 8a and flat, non-lens portions 8b and in positioned adjacent layer 3. As shown lens screen 8 also has pitch A. Lens screen 8 may comprise just cylindrical lenses 8a adjacent each other. If the distances as shown in Fig. 2 are such that lY/b = 5, lC/b = 4 and lM/b = 3, the images of the yellow, cyan and magenta colours filters 7Y, 7C and 7M are respectively formed on the layer 3, as indicated by 9Y, 9C and 9M, at pitches of A/5, A/4 and A/3, and the frequencies of output signals produced by scanning these images are respectively 5fL, 4fL and 3fL (fL being the line scanning frequency). Thus the vidicon tube produces luminance, green, red and blue signals 10Y, 10G, 10R and 10B respectively, Fig. 3, which are separated by filters 12Y-12B, Fig. 1, detected 14G-14B and delayed DL, and matrixed 13 to derive the red, green and blue output video signals. To cut off the high frequency component of the luminance signal so that it does not overlap the colours bands the surface of each flat portion of lens screen 8 may be slightly roughened. Only one of the colour filters is accurately focused into an image, the others being a little out of focus, Fig. 4 (not shown). In a further embodiment the pitch of the colour filters is twice that of the cylindrical lenses and the filters 7Y, 7C and 7M are respectively disposed at positions 11b, 9b and 7b, resulting in blue, red and green colour signals of 5.5fL, 4.5fL and 3.5fL respectively. The pitches of the colour filters need not be the same e.g. the pitch of the cyan filter may be half that of the yellow and magenta filters, Fig. 6 (not shown). Further, the colour filters need not be separated from one another e.g. the yellow and magenta filters may be disposed at the same position, their pitches being different, Fig. 7 (not shown). By overlapping the images of the colour filters through adjacent cylindrical lenses the pitch of the filter regions of the colour filters may be enlarged twice whilst still maintaining the pitches of the images of the filter regions focused on the photoconductive layer constant Fig. 8 (not shown). A separate pick-up tube may be used to produce a luminance signal. In a further embodiment Fig. 9 (not shown) the pitch of the cylindrical lenses is not integrally related to the pitches of the colour filters, and for the images of each colour filter formed by the cylindrical lenses to coincide the position of each colour filter must satisfy the equation 1 + (l)/(b) = (d)/(A) #<SP>1</SP>, where l is the distance from the lens screen to the colour filter, b is the distance from the lens screen to the photoelectric conversion layer of the pick-up tube, A and d are respectively the pitches of the lens screen and the colour filter and #<SP>1</SP> is a positive integer, and the values of d and l for each of the colour filters are selected so that the pitches of the images of the respective filter regions are all different and have values corresponding to (db)/(l).