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代码说明：
A motion picture presents a continues phenomena as a sequence of frames. We perceive continuity by "filling in the gaps" and "smoothing out " the missing information. While faster motion requires more frames during a given time period, there is a point where more frames per second yield no further improvement. The "sampling speed" must be fast enough to allow "appropriate averaging of dead times between frames", but need not accommodate motion too fast to be seen by a human. The above description is somewhat analogous to sampling of audio signals. The sampling rate depends on how fast the signals vary (the highest frequency we hear). Nyquist showed that sampling frequency exceeding twice the audio bandwidth is sufficient to include all the signal information, preserving the finest details up to half the sampling rate
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