获取图片高宽

gistfile1.c

bool GetImageSize(const char *fn, int *x,int *y)
{
    FILE *f=fopen(fn,"rb");
    if (f==0) return false;
    fseek(f,0,SEEK_END);
    long len=ftell(f);
    fseek(f,0,SEEK_SET);
    if (len<24) {
        fclose(f);
        return false;
        }
    cout << fn << endl;
  // Strategy:
  // reading GIF dimensions requires the first 10 bytes of the file
  // reading PNG dimensions requires the first 24 bytes of the file
  // reading JPEG dimensions requires scanning through jpeg chunks
  // In all formats, the file is at least 24 bytes big, so we'll read that always
  unsigned char buf[24]; fread(buf,1,24,f);

  // For JPEGs, we need to read the first 12 bytes of each chunk.
  // We'll read those 12 bytes at buf+2...buf+14, i.e. overwriting the existing buf.
  if (buf[0]==0xFF && buf[1]==0xD8 && buf[2]==0xFF && buf[3]==0xE0 && buf[6]=='J' && buf[7]=='F' && buf[8]=='I' && buf[9]=='F')
  { long pos=2;
    while (buf[2]==0xFF)
    { if (buf[3]==0xC0 || buf[3]==0xC1 || buf[3]==0xC2 || buf[3]==0xC3 || buf[3]==0xC9 || buf[3]==0xCA || buf[3]==0xCB) break;
      pos += 2+(buf[4]<<8)+buf[5];
      if (pos+12>len) break;
      fseek(f,pos,SEEK_SET); fread(buf+2,1,12,f);
    }
  }

  fclose(f);

  // JPEG: (first two bytes of buf are first two bytes of the jpeg file; rest of buf is the DCT frame
  if (buf[0]==0xFF && buf[1]==0xD8 && buf[2]==0xFF)
  { *y = (buf[7]<<8) + buf[8];
    *x = (buf[9]<<8) + buf[10];
    //cout << *x << endl;
    return true;
  }

  // GIF: first three bytes say "GIF", next three give version number. Then dimensions
  if (buf[0]=='G' && buf[1]=='I' && buf[2]=='F')
  { *x = buf[6] + (buf[7]<<8);
    *y = buf[8] + (buf[9]<<8);
    return true;
  }

  // PNG: the first frame is by definition an IHDR frame, which gives dimensions
  if ( buf[0]==0x89 && buf[1]=='P' && buf[2]=='N' && buf[3]=='G' && buf[4]==0x0D && buf[5]==0x0A && buf[6]==0x1A && buf[7]==0x0A
    && buf[12]=='I' && buf[13]=='H' && buf[14]=='D' && buf[15]=='R')
  { *x = (buf[16]<<24) + (buf[17]<<16) + (buf[18]<<8) + (buf[19]<<0);
    *y = (buf[20]<<24) + (buf[21]<<16) + (buf[22]<<8) + (buf[23]<<0);
    return true;
  }

  return false;
}