外文翻譯---電視信號-文庫吧
2025-04-17 09:02 本頁面
【正文】 s to the gray scale of the image, with brighter values being in the direction away from the sync pulses. This place the sync beyond the black range. In video jargon, the sync pulses are said to be blacker than black.. The hardware used for analogtodigital conversion of video signals is called a frame grabber. This is usually in the form of an electronics card that plugs into a puter, and connects to a camera through a coaxial cable. Upon mand from software, the frame grabber waits for the beginning of the next frame, as indicated by the vertical sync pulses. During the following two fields,each line of video is sampled many times, typically 512,640 or 720 samples per line, at 8bits per sample. These samples are stored in memory as one row of the digital image. This way of acquiring a digital image results in an important difference between the vertical and horizontal directions. Each row in the digital image corresponds to one line in the video signal, and therefore to one row of wells in the CCD. Unfortunately, the columns are not so straightforward. In the CCD, each row contains between about 400 and 800 wells (columns), depending on the particular device used. When a row of wells is read from the CCD, the resulting line of video is filtered into a smooth analog signal, such as in Figure . In other words, the video signal does not depend on how many columns are present in the CCD. The resolution in the horizontal direction is limited by how rapidly the analog signal is allowed to change. This is usually set at MHz for color television, resulting in a rise time of about 100 nanoseconds, , about 1/500th of
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