TIFF图像文件格式详解(4)

代码基本取自dcraw(www.cybercom.net/~dcoffin/dcraw/) 做了一些修改和整理

 

//首先定义一些必须的全局变量和一些有用的函数,主要是读取各种数据类型的函数

short order;

FILE *ifp = ifp = fopen ("filename.tiff", "rb");

 

ushort CLASS sget2 (uchar *s)
{
  if (order == 0x4949)  /* "II" means little-endian */
    return s[0] | s[1] << 8;
  else    /* "MM" means big-endian */
    return s[0] << 8 | s[1];
}

ushort CLASS get2()
{
  uchar str[2] = { 0xff,0xff };
  fread (str, 1, 2, ifp);
  return sget2(str);
}

unsigned CLASS sget4 (uchar *s)
{
  if (order == 0x4949)
    return s[0] | s[1] << 8 | s[2] << 16 | s[3] << 24;
  else
    return s[0] << 24 | s[1] << 16 | s[2] << 8 | s[3];
}
#define sget4(s) sget4((uchar *)s)

unsigned CLASS get4()
{
  uchar str[4] = { 0xff,0xff,0xff,0xff };
  fread (str, 1, 4, ifp);
  return sget4(str);
}

unsigned CLASS getint (int type)
{
  return type == 3 ? get2() : get4();
}

float CLASS int_to_float (int i)
{
  union { int i; float f; } u;
  u.i = i;
  return u.f;
}

double CLASS getreal (int type)
{
  union { char c[8]; double d; } u;
  int i, rev;

  switch (type) {
    case 3: return (unsigned short) get2();
    case 4: return (unsigned int) get4();
    case 5:  u.d = (unsigned int) get4();
      return u.d / (unsigned int) get4();
    case 8: return (signed short) get2();
    case 9: return (signed int) get4();
    case 10: u.d = (signed int) get4();
      return u.d / (signed int) get4();
    case 11: return int_to_float (get4());
    case 12:
      rev = 7 * ((order == 0x4949) == (ntohs(0x1234) == 0x1234));
      for (i=0; i < 8; i++)
 u.c[i ^ rev] = fgetc(ifp);
      return u.d;
    default: return fgetc(ifp);
  }
}

 

//先解IFH,得到order和第一个IFD的偏移量

//然后解IFD

//最后是图像数据

//对于多个IFD,采用同样的处理方法

int CLASS parse_tiff ()
{
  int doff;

  fseek (ifp, 0, SEEK_SET);
  order = get2();//"II"或者"MM"
  get2();//这个值应该是42, 跳过之
  doff = get4();//第一个IFD的偏移量
  fseek (ifp, doff, SEEK_SET);
  parse_tiff_ifd ();

  //根据从Tag中得到的值去获取或者解压相应的图像数据
}

 

int CLASS parse_tiff_ifd ()
{
  entries = get2();
  if (entries > 512) return 1;
  while (entries--) {

      //先读取Tag,Type和Count的值

      //根据Type和Count确定存储的是值还是位置,

  }  

  //获取下一个IFD的偏移量

}