/// <summary>
/// 读取包含的Exif元数据APP1部分
/// </summary>
private void ReadAPP1()
{
// Find the APP1 section containing Exif metadata
app1 = file.Sections.Find(a => (a.Marker == JPEGMarker.APP1) &&
(Encoding.ASCII.GetString(a.Header, 0, 6) == "Exif\0\0"));
// If there is no APP1 section, add a new one after the last APP0 section (if any).
if (app1 == null)
{
int insertionIndex = file.Sections.FindLastIndex(a => a.Marker == JPEGMarker.APP0);
if (insertionIndex == -1)
{
insertionIndex = 0;
}
insertionIndex++;
ByteOrder = BitConverterEx.ByteOrder.BigEndian;
app1 = new JPEGSection(JPEGMarker.APP1);
file.Sections.Insert(insertionIndex, app1);
return;
}
byte[] header = app1.Header;
SortedList <int, IFD> ifdqueue = new SortedList <int, IFD>();
makerNoteOffset = 0;
// TIFF header
int tiffoffset = 6;
if (header[tiffoffset] == 0x49)
{
ByteOrder = BitConverterEx.ByteOrder.LittleEndian;
}
else
{
ByteOrder = BitConverterEx.ByteOrder.BigEndian;
}
BitConverterEx conv = new BitConverterEx(ByteOrder, BitConverterEx.ByteOrder.System);
// Offset to 0th IFD
int ifd0offset = (int)conv.ToUInt32(header, tiffoffset + 4);
ifdqueue.Add(ifd0offset, IFD.Zeroth);
int thumboffset = -1;
int thumblength = 0;
int thumbtype = -1;
// Read IFDs
while (ifdqueue.Count != 0)
{
int ifdoffset = tiffoffset + ifdqueue.Keys[0];
IFD currentifd = ifdqueue.Values[0];
ifdqueue.RemoveAt(0);
// Field count
ushort fieldcount = conv.ToUInt16(header, ifdoffset);
for (short i = 0; i < fieldcount; i++)
{
// Read field info
int fieldoffset = ifdoffset + 2 + 12 * i;
ushort tag = conv.ToUInt16(header, fieldoffset);
ushort type = conv.ToUInt16(header, fieldoffset + 2);
uint count = conv.ToUInt32(header, fieldoffset + 4);
byte[] value = new byte[4];
Array.Copy(header, fieldoffset + 8, value, 0, 4);
// Fields containing offsets to other IFDs
if (currentifd == IFD.Zeroth && tag == 0x8769)
{
int exififdpointer = (int)conv.ToUInt32(value, 0);
ifdqueue.Add(exififdpointer, IFD.EXIF);
}
else if (currentifd == IFD.Zeroth && tag == 0x8825)
{
int gpsifdpointer = (int)conv.ToUInt32(value, 0);
ifdqueue.Add(gpsifdpointer, IFD.GPS);
}
else if (currentifd == IFD.EXIF && tag == 0xa005)
{
int interopifdpointer = (int)conv.ToUInt32(value, 0);
ifdqueue.Add(interopifdpointer, IFD.Interop);
}
// Save the offset to maker note data
if (currentifd == IFD.EXIF && tag == 37500)
{
makerNoteOffset = conv.ToUInt32(value, 0);
}
// Calculate the bytes we need to read
uint baselength = 0;
if (type == 1 || type == 2 || type == 7)
{
baselength = 1;
}
else if (type == 3)
{
baselength = 2;
}
else if (type == 4 || type == 9)
{
baselength = 4;
}
else if (type == 5 || type == 10)
{
baselength = 8;
}
uint totallength = count * baselength;
// If field value does not fit in 4 bytes
// the value field is an offset to the actual
// field value
int fieldposition = 0;
if (totallength > 4)
{
fieldposition = tiffoffset + (int)conv.ToUInt32(value, 0);
value = new byte[totallength];
Array.Copy(header, fieldposition, value, 0, totallength);
}
// Compressed thumbnail data
if (currentifd == IFD.First && tag == 0x201)
{
thumbtype = 0;
thumboffset = (int)conv.ToUInt32(value, 0);
}
else if (currentifd == IFD.First && tag == 0x202)
{
thumblength = (int)conv.ToUInt32(value, 0);
}
// Uncompressed thumbnail data
if (currentifd == IFD.First && tag == 0x111)
{
thumbtype = 1;
// Offset to first strip
if (type == 3)
{
thumboffset = (int)conv.ToUInt16(value, 0);
}
else
{
thumboffset = (int)conv.ToUInt32(value, 0);
}
}
else if (currentifd == IFD.First && tag == 0x117)
{
thumblength = 0;
for (int j = 0; j < count; j++)
{
if (type == 3)
{
thumblength += (int)conv.ToUInt16(value, 0);
}
else
{
thumblength += (int)conv.ToUInt32(value, 0);
}
}
}
// Create the exif property from the interop data
ExifProperty prop = ExifPropertyFactory.Get(tag, type, count, value, ByteOrder, currentifd);
Properties.Add(prop.Tag, prop);
}
// 1st IFD pointer
int firstifdpointer = (int)conv.ToUInt32(header, ifdoffset + 2 + 12 * fieldcount);
if (firstifdpointer != 0)
{
ifdqueue.Add(firstifdpointer, IFD.First);
}
// Read thumbnail
if (thumboffset != -1 && thumblength != 0 && Thumbnail == null)
{
if (thumbtype == 0)
{
using (MemoryStream ts = new MemoryStream(header, tiffoffset + thumboffset, thumblength))
{
Thumbnail = new JPEGFile(ts);
}
}
}
}
}
/// <summary>
/// Initializes a new instance of the <see cref="ExifFile" /> class.
/// </summary>
/// <param name="stream">A <see cref="Sytem.IO.Stream" /> that contains image data.</param>
/// <param name="encoding">The encoding to be used for text metadata when the source encoding is unknown.</param>
protected internal JPEGFile(Stream stream, Encoding encoding)
{
Format = ImageFileFormat.JPEG;
Sections = new List <JPEGSection>();
TrailingData = new byte[0];
Encoding = encoding;
stream.Seek(0, SeekOrigin.Begin);
// Read the Start of Image (SOI) marker. SOI marker is represented
// with two bytes: 0xFF, 0xD8.
var markerbytes = new byte[2];
if (stream.Read(markerbytes, 0, 2) != 2 || markerbytes[0] != 0xFF || markerbytes[1] != 0xD8)
{
throw new NotValidJPEGFileException();
}
stream.Seek(0, SeekOrigin.Begin);
// Search and read sections until we reach the end of file.
while (stream.Position != stream.Length)
{
// Read the next section marker. Section markers are two bytes
// with values 0xFF, 0x?? where ?? must not be 0x00 or 0xFF.
if (stream.Read(markerbytes, 0, 2) != 2 || markerbytes[0] != 0xFF || markerbytes[1] == 0x00 ||
markerbytes[1] == 0xFF)
{
throw new NotValidJPEGFileException();
}
var marker = (JPEGMarker)markerbytes[1];
var header = new byte[0];
// SOI, EOI and RST markers do not contain any header
if (marker != JPEGMarker.SOI && marker != JPEGMarker.EOI &&
!(marker >= JPEGMarker.RST0 && marker <= JPEGMarker.RST7))
{
// Length of the header including the length bytes.
// This value is a 16-bit unsigned integer
// in big endian byte-order.
var lengthbytes = new byte[2];
if (stream.Read(lengthbytes, 0, 2) != 2)
{
throw new NotValidJPEGFileException();
}
long length = BitConverterEx.BigEndian.ToUInt16(lengthbytes, 0);
// Read section header.
header = new byte[length - 2];
var bytestoread = header.Length;
while (bytestoread > 0)
{
var count = Math.Min(bytestoread, 4 * 1024);
var bytesread = stream.Read(header, header.Length - bytestoread, count);
if (bytesread == 0)
{
throw new NotValidJPEGFileException();
}
bytestoread -= bytesread;
}
}
// Start of Scan (SOS) sections and RST sections are immediately
// followed by entropy coded data. For that, we need to read until
// the next section marker once we reach a SOS or RST.
var entropydata = new byte[0];
if (marker == JPEGMarker.SOS || (marker >= JPEGMarker.RST0 && marker <= JPEGMarker.RST7))
{
var position = stream.Position;
// Search for the next section marker
while (true)
{
// Search for an 0xFF indicating start of a marker
var nextbyte = 0;
do
{
nextbyte = stream.ReadByte();
if (nextbyte == -1)
{
throw new NotValidJPEGFileException();
}
}while ((byte)nextbyte != 0xFF);
// Skip filler bytes (0xFF)
do
{
nextbyte = stream.ReadByte();
if (nextbyte == -1)
{
throw new NotValidJPEGFileException();
}
}while ((byte)nextbyte == 0xFF);
// Looks like a section marker. The next byte must not be 0x00.
if ((byte)nextbyte != 0x00)
{
// We reached a section marker. Calculate the
// length of the entropy coded data.
stream.Seek(-2, SeekOrigin.Current);
var edlength = stream.Position - position;
stream.Seek(-edlength, SeekOrigin.Current);
// Read entropy coded data
entropydata = new byte[edlength];
var bytestoread = entropydata.Length;
while (bytestoread > 0)
{
var count = Math.Min(bytestoread, 4 * 1024);
var bytesread = stream.Read(entropydata, entropydata.Length - bytestoread, count);
if (bytesread == 0)
{
throw new NotValidJPEGFileException();
}
bytestoread -= bytesread;
}
break;
}
}
}
// Store section.
var section = new JPEGSection(marker, header, entropydata);
Sections.Add(section);
// Some propriety formats store data past the EOI marker
if (marker == JPEGMarker.EOI)
{
var bytestoread = (int)(stream.Length - stream.Position);
TrailingData = new byte[bytestoread];
while (bytestoread > 0)
{
var count = Math.Min(bytestoread, 4 * 1024);
var bytesread = stream.Read(TrailingData, TrailingData.Length - bytestoread, count);
if (bytesread == 0)
{
throw new NotValidJPEGFileException();
}
bytestoread -= bytesread;
}
}
}
// Read metadata sections
ReadJFIFAPP0();
ReadJFXXAPP0();
ReadExifAPP1();
// Process the maker note
_makerNoteProcessed = false;
}
