This paper describes the Advanced High-density Disc AHD system that makes continuous recording of digital audio signals and digital still pictures. The transmission rate for digital audio is 1.4 Mbps, and the still pictures are recorded at the same rate. On the other hand, the transmission rate required for digital video signal is by far higher than this; for examples, the digital TV system specified by CCIR deals with signal at a rate as high as 150 Mbps. This AHD disc system incorporates a picture memory circuit for recording and reproduction that performs transmission rate conversion. Currently, three types of AHD picture systems are available. The frame memory comes in four formats: A (192 Kbytes), B (384 Kbytes), C (640 Kbytes), and D (2560 Kbytes). For these formats, the picture transmission takes 1.2 sec, 2.4 sec, 3.8 sec, and 15 sec, respectively. The B format is standard, with 456 x 572 effective pixels. The A format compresses the same information to half in a checkerboard pattern. The D format transmits high-definition natural pictures, the number of effective pixels being 1280 x 1024. The C format transmits the luminance component of the signal handled in the D format in half of the bits, that is, 4 bits. In any of these formats, the scene shot by a TV camera is converted into an electrical signal and stored in the frame memory after A/D conversion. The stored information is supplied as a signal at a rate matching the digital audio mastering system for recording and editing on digital master tape. Disc cutting and reproduction are also performed on the digital audio system. The information is fed to the frame memory and then output as a high-speed digital video signal so that the reproduced picture suffers little or no deterioration.
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