Color imaging apparatus with closed-loop control means for producing color signal frequency and phase control signals from a reference color signal and two reference index signals stored in a memory

Claim 1

Color imaging apparatus wherein an optical color image is focused on a photoelectrical conversion target of a color image pickup tube through a color stripe filter having a plurality of successively arranged recurrent groups of different color stripes and converted to an electrostatic image which is scanned line-by-line in an image incident area within a rectangular raster scan area of said target by an electron beam to generate a color-mulitiplexed video signal, wherein said video signal has a frequency inversely proportional to the intervals at which said recurrent groups are arranged, said video signal varying in phase with the relative values of primary color components contained in the color image passing through the stripes of each group and in amplitude with the intensity of said primary color components, said video signal containing a phase deviation representing spatial differences between the stripes of each group and a phase deviation representing nonlinearity in the speed of said electron beam in the direction of said line-by-line scan, comprising: index means comprising first and second portions of said target adjacent to edges of said image incident area and within said rectangular raster scan area which are scanned by said electron beam at periodic intervals for generating first and second index signals from said first and second portions, respectively, said first portion being located to be scanned at the beginning of each line; a field memory; reading and writing means for writing into the memory during a write mode said first and second index signals and a video signal having a duration of at least one field derived from said target when the target is uniformly illuminated by light of a predetermined color passing through said color filter and for repeatedly reading the memory during a read mode to generate first and second reference index signals and a reference video signal; closed-loop control means operable during the read mode for deriving frequency and phase control signals from said first and second reference index signals from said memory and said first and second index signals from said index means and for controlling the frequency and phase relationships between said reference video signal from said memory and said color-multiplexed video signal from said target in response to said frequency and phase control signals; and demodulating means for deriving color signals from the color-multiplexed video signal and the reference video signal between which the frequency and phase relationships are controlled by said closed-loop control means.