Abstract: An improved video phone which transmits a source image over a standard telephone line in conjunction with audio voice signals is disclosed. The unique initialization protocol allows asynchronous transmission with its short format. The protocol format provides for a hardware preamble for synchronizing a receiver clock, a software preamble for identifying the video image and disabling the audio, automatic gain control adjustment data and amplitude calibration data. The audio portion is disabled by coupling a capacitor across the telephone to effectively short the telephone. The telephone is placed across the bridge circuit which is provided with switches to balance the bridge in both the telephone audio and the video modes. The transmitted as well as the received signal are passed through the same delay equalization circuit, so that half the delay equalization is done before transmission, with the remaining half being done after reception.

Abstract: A still picture picturephone communication system for transmitting and receiving a still picture over a telephone circuit including a handshaking process wherein prior to still picture transmission, identification code data indicating a function of the picturephone set is transmitted and received, and a decision is made as to whether the still picture is being transmitted or not. A designation code of a desired response waiting time within an identification code data used at the time of handshaking is formed, and the response is delayed by a period of time corresponding to the response waiting time. A still picture data is directly transmitted and received without handshaking. In addition character data including character information and the like can be transmitted and received, and by manipulating the picturephone set of one party the picturephone set of the other party can be made to transmit picture data therefrom. Furthermore, the picture sent from the called party can be transferred to a third party.

Abstract: An improved video phone transmits a source image over a standard telephone line in conjunction with voice signals. The unique initialization protocol provides a hardware preamble for synchronizing a receiver clock, a software preamble for identifying the video image and disabling the audio, automatic gain control adjustment data and amplitude calibration data. The audio portion is disabled by coupling a capacitor across the telephone to effectively short the telephone. The telephone is placed across a bridge circuit which is provided with switches to balance the bridge in both the telephone and video modes. The transmitted and received signals pass through the same delay equalization circuit, so that half the equalization is done before transmission, with the remaining half being done after reception. Input and output selectors allow the same circuit to be used. The digital signals are level shifted up prior to being converted into analog, and then are shifted down again to reduce the effects of DC offset.

Abstract: The present invention is a conversational freeze-frame video phone which transmits a source image over a standard telephone line in conjunction with audio voice signals. A camera is used to capture an image to be transmitted and the image is mapped onto an image field of 2,000 to 5,000 pixels. The image field is displayed on a display area of approximately one square inch on a display screen. Digitized data representing the pixels is asynchronously transmitted on a modulated signal in a single burst of less than three seconds duration. Corresponding remote images are asynchronously received, demodulated, and displayed. The transmission of the audio signal is interrupted upon the detection of a video image being transmitted.