Vertical subsampling and memory synchronization system for a picture within a picture television receiver

Claim 1

In a pix-in-pix television display including a source of main video signal and a source of sampled data auxiliary video signal having a predetermined sample rate, each of said signals being composed of successive horizontal line intervals, apparatus for displaying an image developed from the auxiliary signal as an inset in the image developed from the main signal, comprising: horizontal subsampling means, coupled to said source of sampled data auxiliary video signal for subsampling said auxiliary video signal in a ratio of one to M to develop a horizontally subsampled auxiliary video signal; vertical subsampling means, coupled to said horizontal subsampling means including: first and second buffer means, each of which includes a memory having a sufficient number of bits to hold the samples provided by said horizontal subsampling means during one horizontal line interval of said auxiliary video signal; and means coupled to said horizontal subsampling means for developing, in said first and second memories, during respective first and second time intervals, first and second horizontal line intervals of vertically subsampled auxiliary video signal representing the samples provided by said horizontal subsampling means during respective first and second groups of N horizontal line intervals of said auxiliary video signal; a field memory, having a sufficient number of bits to hold a number of samples of said vertically subsampled auxiliary signal substantially equal to the number of samples in a field of said inset auxiliary image; memory reading means, coupled to said field memory for reading samples, representing a horizontal line interval of said vertically subsampled auxiliary video signal, from said field memory for display during a predetermined portion of a horizontal line interval of said main video signal; and memory writing means, coupled to said buffer means, to said field memory and to said memory reading means for sequentially writing samples from the respective first and second memories of said buffer means to said field memory during said second and first time intervals respectively, and being controlled by said memory reading means to suspend writing samples into said field memory when said reading means reads samples from said field memory and to resume writing samples into said field memory when said reading means has stopped reading samples from said field memory, whereby one horizontal line interval of vertically subsampled auxiliary video signal from said vertical subsampling means may be written into said field memory during portions of N horizontal line intervals of said auxiliary video signal.