理解频域处理与空间域处理的等效关系与步骤，掌握频域相乘与空间域循环卷积之间的对等关系，理解DFT运算中补零的效果。(Understand the equivalent relationship and steps of frequency domain processing and space domain processing, understand the reciprocal relationship between frequency domain multiplication and space domain circular convolution, and understand the effect of zero padding in DFT operation.)