private bool ProcessApp1Data(byte[] data, out DateTime dateTaken)
{
dateTaken = DateTime.MinValue;
if (CheckTiffHeader(data, out bool isLittleEndian, out int ifdOffset) == false || ifdOffset <= 0)
{
return(false);
}
int workOffset = ifdOffset;
bool isSubstituteFound = false;
DateTime substituteDateTaken = DateTime.MinValue;
while (workOffset > 0)
{
workOffset += 6; // 6 is exif header size
// exif spec says all offsets start from tiff header, but current buffer starts from exif header
int directoryCount;
if (isLittleEndian)
{
directoryCount = BitConverter.ToInt16(data, workOffset);
}
else
{
directoryCount = BitConverterBE.ToInt16(data, workOffset);
}
workOffset += 2;
bool subIFDFound = false;
for (int i = 0; i < directoryCount; i++)
{
var ifd = ImageFileDirectory.Read(isLittleEndian, data, workOffset);
if (ifd.Tag == SUBIFD)
{
if (isLittleEndian)
{
workOffset = BitConverter.ToInt32(ifd.Value.Array, ifd.Value.Offset);
}
else
{
workOffset = BitConverterBE.ToInt32(ifd.Value.Array, ifd.Value.Offset);
}
subIFDFound = true;
break;
}
if (ifd.Tag == 306)
{
if (ifd.Type != 2 || ifd.Value.Count != 20)
{
continue;
}
isSubstituteFound = TryParseDateTime(ifd.Value.Array, ifd.Value.Offset, ifd.Value.Count, out substituteDateTaken);
}
else if (ifd.Tag == 0x9003 || ifd.Tag == 0x9004)
{
if (ifd.Type != 2 || ifd.Value.Count != 20)
{
return(false);
}
if (TryParseDateTime(ifd.Value.Array, ifd.Value.Offset, ifd.Value.Count, out dateTaken))
{
return(true);
}
}
workOffset += 12;
}
if (subIFDFound)
{
continue;
}
if (isLittleEndian)
{
workOffset = BitConverter.ToInt32(data, workOffset);
}
else
{
workOffset = BitConverterBE.ToInt32(data, workOffset);
}
}
if (isSubstituteFound)
{
dateTaken = substituteDateTaken;
return(true);
}
return(false);
}
internal static ImageFileDirectory Read(bool isLittleEndian, byte[] data, int offset)
{
var ifd = new ImageFileDirectory();
if (isLittleEndian)
{
ifd.Tag = BitConverter.ToUInt16(data, offset);
}
else
{
ifd.Tag = BitConverterBE.ToUInt16(data, offset);
}
if (isLittleEndian)
{
ifd.Type = BitConverter.ToUInt16(data, offset + 2);
}
else
{
ifd.Type = BitConverterBE.ToUInt16(data, offset + 2);
}
uint components;
uint dataOffset;
if (isLittleEndian)
{
components = BitConverter.ToUInt32(data, offset + 4);
}
else
{
components = BitConverterBE.ToUInt32(data, offset + 4);
}
if (isLittleEndian)
{
dataOffset = BitConverter.ToUInt32(data, offset + 8) + 6;
}
else
{
dataOffset = BitConverterBE.ToUInt32(data, offset + 8) + 6;
}
uint componentSize = 1;
if (ifd.Type == 3 || ifd.Type == 8)
{
componentSize = 2;
}
else if (ifd.Type == 4 || ifd.Type == 9 || ifd.Type == 11)
{
componentSize = 4;
}
else if (ifd.Type == 5 || ifd.Type == 10 || ifd.Type == 12)
{
componentSize = 8;
}
uint totalByteLength = componentSize * components;
if (totalByteLength <= 4)
{
ifd.Value = new ArraySegment <byte>(data, offset + 8, (int)totalByteLength);
}
else
{
ifd.Value = new ArraySegment <byte>(data, (int)dataOffset, (int)totalByteLength);
}
return(ifd);
}
