java支持的图片格式有jpg、png、gif。本代码提供了bmp、pgm、ppm图像文件的读入，是《数字图像处理-java编程与实验》书上代码，仅供参考，允许非商业的借鉴。-Java support image formats have JPG, PNG, GIF. This code provides BMP, PGM, PPM image file to read, it is the digital image processing- Java programming and exper

读出PGM格式图像, 可以进一步进行图像处理-read a PGM-type image, can be used for image processing.