private static Size DecodeJfif(SequentialBinaryReader reader)
{
reader.IsBigEndian = true;
var magicNumber = reader.ReadUInt16(); // first two bytes should be JPEG magic number
do
{
// Find next segment marker. Markers are zero or more 0xFF bytes, followed
// by a 0xFF and then a byte not equal to 0x00 or 0xFF.
byte segmentIdentifier = reader.ReadByte();
byte segmentType = reader.ReadByte();
// Read until we have a 0xFF byte followed by a byte that is not 0xFF or 0x00
while (segmentIdentifier != 0xFF || segmentType == 0xFF || segmentType == 0)
{
segmentIdentifier = segmentType;
segmentType = reader.ReadByte();
}
if (segmentType == 0xD9) // EOF?
{
return(Size.Empty);
}
// next 2-bytes are <segment-size>: [high-byte] [low-byte]
var segmentLength = (int)reader.ReadUInt16();
// segment length includes size bytes, so subtract two
segmentLength -= 2;
if (segmentType == 0xC0 || segmentType == 0xC2)
{
reader.ReadByte(); // bits/sample, usually 8
int height = (int)reader.ReadUInt16();
int width = (int)reader.ReadUInt16();
return(new Size(width, height));
}
else
{
// skip this segment
reader.Skip(segmentLength);
}
}while (true);
}
/// <summary>
/// Examines the a file's first bytes and estimates the file's type.
/// </summary>
private static FileType DetectFileType(SequentialBinaryReader reader)
{
byte[] magicBytes = new byte[MaxMagicBytesLength];
for (int i = 0; i < MaxMagicBytesLength; i += 1)
{
magicBytes[i] = reader.ReadByte();
foreach (var kvPair in imageFormatDecoders)
{
if (StartsWith(magicBytes, kvPair.Key))
{
return(kvPair.Value);
}
}
}
return(FileType.Unrecognized);
}