imreadwrite.c

计算机视觉-计算理论与算法基础

/*
 * Description: 
 * 
 * Procedures to read/write an image in PGM format
 */
#include <stdio.h>
#include <fcntl.h>

/*
 * constants
 */
#define OK 1
#define ERROR 0

/* forward declarations */
static char imPgmReadChar(int fd);
static int imPgmReadInt(int fd);

/*
 * read image. The user needn't allocate image buffer.
 *
 * Returns OK if success; ERROR, otherwise.
 */
int imRead (
           const char *filename,  /* name of file image to read */
           int *pwidth,           /* Nb of columns of the image */
           int *pheight,          /* Nb of rows of the image */
           unsigned char **imgIn) /* Buffer of the image */
{
    int fd;
    int size, dimx, dimy;
    char ImgType[2];
  
    if ((fd=open(filename,O_RDONLY,0666)) == 0) {
        fprintf(stderr,"imRead: opening problem\n");
        return (ERROR);
    }

    *imgIn = NULL;

    if (read (fd, ImgType, sizeof(ImgType)) != sizeof(ImgType)) {
        fprintf (stderr, "imRead: read error\n");
        return (ERROR);
    }

    if (!strncmp (ImgType, "P5", 2)) {
        if((dimx = imPgmReadInt(fd)) == 0 || 
           (dimy = imPgmReadInt(fd)) == 0 || 
           imPgmReadInt(fd) == 0) {
            fprintf(stderr,"imRead: bad PGM header\n");
            if ( fd != 0 )
                close(fd);
            return(ERROR);
        }
        *pwidth = dimx;
        *pheight = dimy;
        size = dimx * dimy;
        if (((*imgIn) = (unsigned char *)malloc(size)) == NULL) 
            return (ERROR);
        if (read (fd, (*imgIn), size) != size) {
            fprintf (stderr, "imRead: read size problem\n");
            if (fd != 0)
                close (fd);
            return (ERROR);
        }
    }
    else {
        return (ERROR);
    }

    close (fd);
    return (OK);
}

static char imPgmReadChar(int fd) /* opened file descriptor of the file */
{
    char c;
    
    if ( read(fd,&c,1) != 1) {
        return((char)ERROR);
    }
    
    if ( c == '#' ) {
        do {
            if ( read(fd,&c,1) != 1) {
                return((char)ERROR);
            }
        } while( (c != '\n') && (c != '\r')) ;
    }
    return (c);
}

static int imPgmReadInt (int fd) /* opened file descriptor of the file */
{
    register char ch;
    register int i;
    
    do {
        ch = imPgmReadChar(fd);
        if ( ch == (char) ERROR ) {
            return(ERROR);
        }
    } while ( ch == ' ' || ch == '\t' || ch == '\n' || ch == '\r' );
    
    if ( ch < '0' || ch > '9' ) {
        fprintf(stderr,"imRead: problem with PGM format\n");
        return(ERROR);
    }
    
    i = 0;
    do {
        i = i * 10 + ch - '0';
        ch = imPgmReadChar(fd); 
        if ( ch == (char) ERROR ) {
            return(ERROR);
        }
    } while ( ch >= '0' && ch <= '9' );
    
    return i;
}

/*
 * write image
 *
 * Returns OK if success; ERROR, otherwise.
 */
int imWrite (
             const char *filename, /* name of file image to read */
             const int width,	   /* Nb of columns of the image */
             const int height,     /* Nb of rows of the image */
             unsigned char *imgIn) /* Buffer of the image */
{    
    int fd;
    int size, nbc;
    char header[256];
    
    size = width * height;
    
    if ((fd=open(filename,O_WRONLY|O_CREAT,0666)) == 0) {
        fprintf(stderr, "imRead: opening problem\n");
        return (ERROR);
    }
    
    sprintf (header, "P5\n%d %d\n255\n", width, height);
    write (fd, header, strlen(header));
    nbc = write (fd, imgIn, size);
    if (nbc != size) {
        fprintf (stderr, "imRead: write size problem\n");
        close (fd);
        return (ERROR);
    }
    else {
        close (fd);
        return (OK);
    }  
}