说明：  使用Matlab对图片进行操作时，大量的单张图片不利于操作，此时需要将图片转化为.mat格式，.mat方便我们对数据的处理，使我们更加高效的利用数据。文章中的代码是以PIE数据集作为转换的原始数据，每张图片的名称是连续的数字，相同类别的图片张数相等且名称连续。
(When using MATLAB to operate pictures, a large number of single pictures are not conducive to operation. At this time, we need to convert pictures into. mat format. mat is convenient for us to process data, so that we can use data more efficiently. The code in this article is PIE data set as the original data for conversion. The name of each picture is a continuous number. The number of pictures of the same category is equal and the name is continuous.)