VC图像边缘检测源代码

纯c语言，Function: read_ppm_image * Purpose: This function reads in an image in PPM format. The image can be * read in from either a file or from standard input. The image is only read * from standard input when infilename = NULL. Because the PPM format includes * the number of columns and the number of rows in the image, these are read * from the file. Memory to store the image is allocated in this function. * All comments in the header are discarded in the process of reading the * image. Upon failure, this function returns 0, upon sucess it returns 1.