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美国加利福尼亚州Widcom公司研制出一种数据压缩率达一千多倍的电视信号编译码器,样机型号为VTC-56。用56kbit/s速率传送电视信号,可以供给电视会议使用。整个设备安装在14×20×16英寸的机箱内。VTC-56的压缩技术包括三个连续的处理过程,即滤波、条件刷新和余弦变换编码。利用扫描行间和帧间相关性去除亮度和色彩中的冗余度。数据以8比特/象元隔行扫描的“场”进行处理,首先用数字频谱和时域滤波器滤波,每场从512×512个象元减少到256×256个象元,帧频从每秒30帧减至10帧。帧信息储存在
Widcom, California, USA, developed a TV signal codec with a data compression rate of more than a thousand times. The prototype was VTC-56. With 56kbit / s rate of transmission of television signals, can be used for videoconferencing. The whole device is installed in a 14 × 20 × 16 inch chassis. VTC-56 compression technology includes three consecutive processes, namely, filtering, conditional refresh and cosine transform coding. Redundancy in brightness and color is removed using inter-scan lines and inter-frame correlation. The data is processed in an 8 bit / pixel interlaced “field,” first filtered with digital spectrum and time-domain filters, reducing each field from 512 x 512 pixels to 256 x 256 pixels with a frame rate of from one second 30 frames reduced to 10 frames. The frame information is stored in