Abstract: Disclosed is a method for compressing data which is derived by tracing the contour line of a character pattern or a symbol. Normally such a contour line consists of at least one closed-loop line having straight portions and curved portions. A multiplicity of sampling points are selected along the contour line for the purpose of representing the contour line with these sampling points and those sampling points located along a straight or lightly curved portion of the contour line are disregarded and those located along a curved portion of the contour line are retained because the former have relatively less influence on the representation of the original character or symbol pattern than the latter.

Abstract: A security communication system comprises a transmission apparatus including a scrambling circuit for scrambling an information signal according to a specific code and a reception apparatus including a deciphering circuit for deciphering an output signal of the transmission apparatus according to substantially the same code as the specific code. The transmission apparatus further includes a first signal generating circuit for supplying a synchronizing signal to the scrambling circuit to drive the same, a signal synthesizing circuit having a first input terminal coupled to the output terminal of the first signal generating circuit, and a switching circuit connected between the output terminal of the scrambling circuit and a second input terminal of the signal synthesizing circuit, said switching circuit being opened while the first signal generating circuit is generating a synchronizing signal.

Abstract: In a security communication system, the transmitting unit includes a sample - hold circuit for sampling and holding the original voice signal, an inverting circuit for inverting the polarity of the samples of the voice signal in accordance with a first code, an adder circuit for adding a D.C. signal to the output signal of the inverting circuit, and another inverting circuit for inverting the polarity of the samples of the output signal of the adder circuit in accordance with a second code. The receiving unit includes a sample - hold circuit for sampling and holding the received signal, a synchronizing circuit for extracting a synchronizing signal component from a received signal during, for example a period of non-voice transmission, and for synchronizing the transmitting unit with the receiving unit, an inverting circuit for inverting the polarity of the samples of the received signal in accordance with the second code, a circuit for removing a D.C.