图像文件通常是BMP, JPG类型，

显示的时候往往不需要太大的文件尺寸，

本程序就是用来压缩 BMP --> JPG,

JPG 则可以降低压缩比。-image file is usually BMP, JPG type shows, more often than not too much paper size, This procedure is used to reduce BMP --