外文翻译---电视信号(编辑修改稿)

外文翻译---电视信号(编辑修改稿)内容摘要：

the microsecond video line. When the video signal is digitized in the frame grabber, it is converted back into columns, However, these columns in the digitized image have no relation to the columns in the CCD. The number of columns in the digital image depends solely on how many times the frame grabber samples each line of video. For example, a CCD might have 800 wells per row, while the digitized image might only have 512 pixels ( , columns) per row. The number of columns in the digitized image is also important for another reason. The standard television image has an aspect ratio of 4 to 3, . , it is slightly wider than it is high. Motion pictures have the wider aspect ratio of 25 to 9. CCDs used for scientific applications often have an aspect ratio of 1 to 1, , a perfect square. In any event, the aspect ratio of a CCD is fixed by the placement of the electrodes, and cannot be altered. However, the aspect ratio of the digitized image depends on the number of samples per line. This bees a problem when the image is displayed, either on a video monitor or in a hardcopy. If the aspect ratio isn’t properly reproduced, the image looks squashed horizontally or vertically. The 525 line video signal described here is called NTSC (National Television Systems Committee), a standard defined way back in 1954. This is the system used in the United States and Japan. In Europe there are two similar standards called PAL (Phase Alternation by Line) and SECAM (Sequential Chrominance And Memory). The basic concepts are the same , just the numbers are different. Both PAL and SECAM operate with 25 interlaced frames per secon。