Camcorders
Camcorders (camera recorders) are the most advanced form of ‘domestic’ technology. Combining the elements of camera, encoder, VCR electronics, deck- and lens mechanics and computer control, they draw on the sys- tems, technologies and techniques described in most of the chapters of this book.
Figure 22.21 shows the functional block diagram of a digital camcorder system. Light from the optical lens assembly projects an image onto the
charged coupled device (CCD) imager. The CCD is a photosensitive array which is charged by the light falling on it. The charge is then converted into a continuous analogue voltage when the CCD charged elements are scanned line by line. After the scan is completed, the CCD elements are reset to start the exposure process for the next video frame. Embedded within the CCD is an analogue-to-digital converter to produce a digital output for further processing by the camera processing block ready for data compression by the MPEG codec. The camera processing chip carries out such functions as ‘steady shot’, zoom and focus motor control and dig- ital picture effects. The MPEG-coded data are fed into a video buffer. Digitised Y/C data are also fed into the electronic viewfinder (EVF) for monitoring by the user. Stereo sound from audio microphones are A/D converted and the PCM audio data placed into an audio buffer. The MUX/DEMUX receives the compressed video and PCM audio streams from the corresponding buffers, packetises and multiplexes them into a standard MPEG-2 program stream (PS) to be stored in a PS buffer. Data in the PS buffer are then used to write on the recording medium which could be a DVD disc, an HDD or a magnetic tape. In the playback mode, the process is reversed and this is the reason for using an MPEG codec chip instead of just a coder and MUX/DEMUX instead of just a MUX. In the playback mode, data from the recording medium are demultiplexed and decompressed and fed into the EVF for display.
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