Several extrema may be produced in evaluating function curves,as image noise is caused by interferences in image gathering,quantifying and transmission processes.

• 将数字图像作为处理对象的自动聚焦系统中,由于图像采样、量化及传输过程中各种干扰引起的图像噪音,导致评价函数曲线可能存在多个极值。