Method for a compatible increase in resolution in television systems

A method for effecting a compatible increase in resolution in a television signal transmission system having a transmitting end and a receiving end and in which the luminance signal is scanned line by line, with line interlacing, to divide each picture frame into two fields, and the signal is limited at the transmitting end by a lowpass filter, the transmitting and receiving ends being coupled together by a transmission channel having an upper cutoff frequency defined by a Nyquist edge, said method comprising:

• at the transmitting end,
• sampling elements of successive lines of each field, with the sampled elements of one field being offset in the line scanning direction from those of the immediately succeeding field, the sampling of successive lines being controlled by a sampling clock pulse train at a frequency which is in synchronism with the line scanning frequency of the system and which is twice as high as the frequency at the Nyquist edge of the transmission channel;
• and, at the receiving end,
• sampling the signal received from the transmitting end in synchronism with the sampling clock pulse train at the transmitting end and delayed by the delay time of the transmission channel;
• separately storing the sampled signals associated with the two fields of each picture frame in accordance with the time of their occurrence;
• alternatingly reading out from storage successive sampled signals of immediately adjacent lines of a complete picture frame in the sequence of one sampled signal of one field followed by the next succeeding sampled signal of the immediately succeeding line of a complete picture frame, which next succeeding line forms part of the other field, said reading out occurring at twice the speed at which the sampled signals are stored, and combining the sampled signals into a single signal in the order in which they are read out;
• after reading out the sampled signals of each line, again storing those signals in such a manner that during the time of storing of the signals associated with a frame, the stored signals associated with each field are read out twice and the read out signals occupying one line scanning period contain alternatingly the image points of two immediately adjacent lines of a complete picture frame;
• and
• converting the read-out signals to analog form and combining them with synchronizing signals, and supplying the combined signals to a monitor constructed to produce a cathode ray beam which is wobbled vertically in such a way that during each line sweep the elements of one line of the received signal are displayed at selected locations and the elements of the immediately adjacent line of a complete frame are displayed at locations vertically offset therefrom.

A circuit arrangement for effecting a compatible increase in resolution in a television signal transmission system having a transmitting end and a receiving end and in which the luminance signal is scanned line by line, with line interlacing to divide each picture frame into two fields, the transmitting and receiving ends being coupled together by a transmission channel having an upper cutoff frequency defined by a Nyquist edge, said circuit arrangement comprising:

• at the transmitting end,
• a transmitter lowpass filter connected for passing low frequency components of the scanned luminance signal;
• a transmitter sampling switch having a signal input connected to receive the luminance signal components passed by said filter, a control input, and an output connected to the transmission channel;
• and
• a clock pulse generator connected to said switch control input for supplying thereto sampling clock pulses at a frequency which is in synchronism with the line scanning frequency of the system and is twice the frequency at the Nyquist edge of the transmission channel for causing said switch to sample successive elements of the luminance signal at the clock pulse frequency and to supply to its output a transmitter signal containing synchronizing pulses and signal samples representative of successively sampled elements of successive lines of each field, with the sampled elements of one field being offset in the line scanning direction from those of the immediately succeeding field by an amount equal to one-half the sampling clock pulse period, said clock pulse generator further providing synchronizing signals;
• and at the receiving end,
• a receiver input connected to the transmission channel to receive the transmitter signal;
• means defining a receiver clock pulse center having a synchronizing input connected to said signal input, and first and second outputs, and controllable by the synchronizing pulses in the transmitter signal to supply to its first output receiver sampling pulses at the same frequency as, and delayed in time relative to, the sampling clock pulses supplied by said clock pulse generator;
• a receiver sampling switch having a signal input connected to said receiver input, a signal output, and a control input connected to said first output of said receiver clock pulse center for sampling the transmitter signal in response to each receiver sampling pulse;
• a video memory having a signal input connected to receive the sampled signals appearing at said receiver sampling switch output, a signal output, and two control inputs connected to said control outputs of said receiver clock pulse center for separately reading into said memory the sampled signals associated with the two fields of each picture frame in accordance with the time of their occurrence, alternatingly reading out from storage and combining, at its said signal output, the read-in sampled signals of immediately adjacent lines of a complete picture frame at twice the rate at which they are read-in to provide signals of successive lines of a complete frame at the frame frequency of said step of scanning at the transmitting end, and, after once reading out the signals of each line, again reading-in those signals so that during the time of reading-in of the signals associated with a frame, the read-in signals associated with each field are read out twice;
• and
• a receiver lowpass filter having an upper cutoff frequency twice that of said transmitter lowpass filter and connected to receive the signals appearing at said video memory signal output, and a television monitor connected to receive, and produce a display based on, the signals passed by said receiver lowpass filter.