A method of determining a transmission process is disclosed. With this structure, the head guard arrangement protects the head and brain of an infant against impact injuries. The decoder board determines the format of the frame of image data from information about which of the plurality of imaging modules provided the frame of image data or from information about the frame of image data, activates as necessary a command to prepare the decoder board to decode the frame of image data according to the format provided by the imaging module, and performs the decoding. The gate of the first generating transistor receives the output of the first differential amplifier.