public DecodedJpeg Decode()
{
// The frames in this jpeg are loaded into a list. There is
// usually just one frame except in heirarchial progression where
// there are multiple frames.
JPEGFrame frame = null;
// The restart interval defines how many MCU's we should have
// between the 8-modulo restart marker. The restart markers allow
// us to tell whether or not our decoding process is working
// correctly, also if there is corruption in the image we can
// recover with these restart intervals. (See RSTm DRI).
int resetInterval = 0;
bool haveMarker = false;
bool foundJFIF = false;
List <JpegHeader> headers = new List <JpegHeader>();
// Loop through until there are no more markers to read in, at
// that point everything is loaded into the jpegFrames array and
// can be processed.
while (true)
{
#region Switch over marker types
switch (marker)
{
case JPEGMarker.APP0:
// APP1 is used for EXIF data
case JPEGMarker.APP1:
// Seldomly, APP2 gets used for extended EXIF, too
case JPEGMarker.APP2:
case JPEGMarker.APP3:
case JPEGMarker.APP4:
case JPEGMarker.APP5:
case JPEGMarker.APP6:
case JPEGMarker.APP7:
case JPEGMarker.APP8:
case JPEGMarker.APP9:
case JPEGMarker.APP10:
case JPEGMarker.APP11:
case JPEGMarker.APP12:
case JPEGMarker.APP13:
case JPEGMarker.APP14:
case JPEGMarker.APP15:
// COM: Comment
case JPEGMarker.COM:
// Debug.WriteLine(string.Format("Extracting Header, Type={0:X}", marker));
JpegHeader header = ExtractHeader();
#region Check explicitly for Exif Data
if (header.Marker == JPEGMarker.APP1 && header.Data.Length >= 6)
{
byte[] d = header.Data;
if (d[0] == 'E' &&
d[1] == 'x' &&
d[2] == 'i' &&
d[3] == 'f' &&
d[4] == 0 &&
d[5] == 0)
{
// Exif. Do something?
}
}
#endregion
#region Check for Adobe header
if (header.Data.Length >= 5 && header.Marker == JPEGMarker.APP14)
{
string asText = UTF8Encoding.UTF8.GetString(header.Data, 0, 5);
if (asText == "Adobe")
{
// ADOBE HEADER. Do anything?
}
}
#endregion
headers.Add(header);
if (!foundJFIF && marker == JPEGMarker.APP0)
{
foundJFIF = TryParseJFIF(header.Data);
if (foundJFIF) // Found JFIF... do JFIF extension follow?
{
header.IsJFIF = true;
marker = jpegReader.GetNextMarker();
// Yes, they do.
if (marker == JPEGMarker.APP0)
{
header = ExtractHeader();
headers.Add(header);
}
else // No. Delay processing this one.
{
haveMarker = true;
}
}
}
break;
case JPEGMarker.SOF0:
case JPEGMarker.SOF2:
// SOFn Start of Frame Marker, Baseline DCT - This is the start
// of the frame header that defines certain variables that will
// be carried out through the rest of the encoding. Multiple
// frames are used in a hierarchical system, however most JPEG's
// only contain a single frame.
// Progressive or baseline?
progressive = marker == JPEGMarker.SOF2;
jpegFrames.Add(new JPEGFrame());
frame = (JPEGFrame)jpegFrames[jpegFrames.Count - 1];
frame.ProgressUpdateMethod = new Action <long>(UpdateStreamProgress);
// Skip the frame length.
jpegReader.ReadShort();
// Bits percision, either 8 or 12.
frame.setPrecision(jpegReader.ReadByte());
// Scan lines (height)
frame.ScanLines = jpegReader.ReadShort();
// Scan samples per line (width)
frame.SamplesPerLine = jpegReader.ReadShort();
// Number of Color Components (channels).
frame.ComponentCount = jpegReader.ReadByte();
DecodeProgress.Height = frame.Height;
DecodeProgress.Width = frame.Width;
DecodeProgress.SizeReady = true;
if (DecodeProgressChanged != null)
{
DecodeProgressChanged(this, DecodeProgress);
}
// Add all of the necessary components to the frame.
for (int i = 0; i < frame.ComponentCount; i++)
{
byte compId = jpegReader.ReadByte();
byte sampleFactors = jpegReader.ReadByte();
byte qTableId = jpegReader.ReadByte();
byte sampleHFactor = (byte)(sampleFactors >> 4);
byte sampleVFactor = (byte)(sampleFactors & 0x0f);
frame.AddComponent(compId, sampleHFactor, sampleVFactor, qTableId);
}
break;
case JPEGMarker.DHT:
// DHT non-SOF Marker - Huffman Table is required for decoding
// the JPEG stream, when we receive a marker we load in first
// the table length (16 bits), the table class (4 bits), table
// identifier (4 bits), then we load in 16 bytes and each byte
// represents the count of bytes to load in for each of the 16
// bytes. We load this into an array to use later and move on 4
// huffman tables can only be used in an image.
int huffmanLength = (jpegReader.ReadShort() - 2);
// Keep looping until we are out of length.
int index = huffmanLength;
// Multiple tables may be defined within a DHT marker. This
// will keep reading until there are no tables left, most
// of the time there are just one tables.
while (index > 0)
{
// Read the identifier information and class
// information about the Huffman table, then read the
// 16 byte codelength in and read in the Huffman values
// and put it into table info.
byte huffmanInfo = jpegReader.ReadByte();
byte tableClass = (byte)(huffmanInfo >> 4);
byte huffmanIndex = (byte)(huffmanInfo & 0x0f);
short[] codeLength = new short[16];
for (int i = 0; i < codeLength.Length; i++)
{
codeLength[i] = jpegReader.ReadByte();
}
int huffmanValueLen = 0;
for (int i = 0; i < 16; i++)
{
huffmanValueLen += codeLength[i];
}
index -= (huffmanValueLen + 17);
short[] huffmanVal = new short[huffmanValueLen];
for (int i = 0; i < huffmanVal.Length; i++)
{
huffmanVal[i] = jpegReader.ReadByte();
}
// Assign DC Huffman Table.
if (tableClass == HuffmanTable.JPEG_DC_TABLE)
{
dcTables[(int)huffmanIndex] = new JpegHuffmanTable(codeLength, huffmanVal);
}
// Assign AC Huffman Table.
else if (tableClass == HuffmanTable.JPEG_AC_TABLE)
{
acTables[(int)huffmanIndex] = new JpegHuffmanTable(codeLength, huffmanVal);
}
}
break;
case JPEGMarker.DQT:
// DQT non-SOF Marker - This defines the quantization
// coeffecients, this allows us to figure out the quality of
// compression and unencode the data. The data is loaded and
// then stored in to an array.
short quantizationLength = (short)(jpegReader.ReadShort() - 2);
for (int j = 0; j < quantizationLength / 65; j++)
{
byte quantSpecs = jpegReader.ReadByte();
int[] quantData = new int[64];
if ((byte)(quantSpecs >> 4) == 0)
// Precision 8 bit.
{
for (int i = 0; i < 64; i++)
{
quantData[i] = jpegReader.ReadByte();
}
}
else if ((byte)(quantSpecs >> 4) == 1)
// Precision 16 bit.
{
for (int i = 0; i < 64; i++)
{
quantData[i] = jpegReader.ReadShort();
}
}
qTables[(int)(quantSpecs & 0x0f)] = new JpegQuantizationTable(quantData);
}
break;
case JPEGMarker.SOS:
Debug.WriteLine("Start of Scan (SOS)");
// SOS non-SOF Marker - Start Of Scan Marker, this is where the
// actual data is stored in a interlaced or non-interlaced with
// from 1-4 components of color data, if three components most
// likely a YCrCb model, this is a fairly complex process.
// Read in the scan length.
//ushort scanLen = jpegReader.ReadShort();
// Number of components in the scan.
byte numberOfComponents = jpegReader.ReadByte();
byte[] componentSelector = new byte[numberOfComponents];
for (int i = 0; i < numberOfComponents; i++)
{
// Component ID, packed byte containing the Id for the
// AC table and DC table.
byte componentID = jpegReader.ReadByte();
byte tableInfo = jpegReader.ReadByte();
int DC = (tableInfo >> 4) & 0x0f;
int AC = (tableInfo) & 0x0f;
frame.setHuffmanTables(componentID,
acTables[(byte)AC],
dcTables[(byte)DC]);
componentSelector[i] = componentID;
}
byte startSpectralSelection = jpegReader.ReadByte();
byte endSpectralSelection = jpegReader.ReadByte();
byte successiveApproximation = jpegReader.ReadByte();
#region Baseline JPEG Scan Decoding
if (!progressive)
{
frame.DecodeScanBaseline(numberOfComponents, componentSelector, resetInterval, jpegReader, ref marker);
haveMarker = true; // use resultant marker for the next switch(..)
}
#endregion
#region Progressive JPEG Scan Decoding
if (progressive)
{
frame.DecodeScanProgressive(
successiveApproximation, startSpectralSelection, endSpectralSelection,
numberOfComponents, componentSelector, resetInterval, jpegReader, ref marker);
haveMarker = true; // use resultant marker for the next switch(..)
}
#endregion
break;
case JPEGMarker.DRI:
jpegReader.BaseStream.Seek(2, System.IO.SeekOrigin.Current);
resetInterval = jpegReader.ReadShort();
break;
// Defines the number of lines. (Not usually present)
case JPEGMarker.DNL:
frame.ScanLines = jpegReader.ReadShort();
break;
// End of Image. Finish the decode.
case JPEGMarker.EOI:
if (jpegFrames.Count == 0)
{
throw new NotSupportedException("No JPEG frames could be located.");
}
else if (jpegFrames.Count == 1)
{
// Only one frame, JPEG Non-Heirarchial Frame.
byte[][,] raster = Image.CreateRaster(frame.Width, frame.Height, frame.ComponentCount);
IList <JpegComponent> components = frame.Scan.Components;
int totalSteps = components.Count * 3; // Three steps per loop
int stepsFinished = 0;
for (int i = 0; i < components.Count; i++)
{
JpegComponent comp = components[i];
comp.QuantizationTable = qTables[comp.quant_id].Table;
// 1. Quantize
comp.quantizeData();
UpdateProgress(++stepsFinished, totalSteps);
// 2. Run iDCT (expensive)
comp.idctData();
UpdateProgress(++stepsFinished, totalSteps);
// 3. Scale the image and write the data to the raster.
comp.writeDataScaled(raster, i, BlockUpsamplingMode);
UpdateProgress(++stepsFinished, totalSteps);
// Ensure garbage collection.
comp = null; GC.Collect();
}
// Grayscale Color Image (1 Component).
if (frame.ComponentCount == 1)
{
ColorModel cm = new ColorModel()
{
ColorSpace = ColorSpace.Gray, Opaque = true
};
image = new Image(cm, raster);
}
// YCbCr Color Image (3 Components).
else if (frame.ComponentCount == 3)
{
ColorModel cm = new ColorModel()
{
ColorSpace = ColorSpace.YCbCr, Opaque = true
};
image = new Image(cm, raster);
}
// Possibly CMYK or RGBA ?
else
{
throw new NotSupportedException("Unsupported Color Mode: 4 Component Color Mode found.");
}
// If needed, convert centimeters to inches.
Func <double, double> conv = x =>
Units == UnitType.Inches ? x : x / 2.54;
image.DensityX = conv(XDensity);
image.DensityY = conv(YDensity);
//height = frame.Height;
//width = frame.Width;
}
else
{
// JPEG Heirarchial Frame
throw new NotSupportedException("Unsupported Codec Type: Hierarchial JPEG");
}
break;
// Only SOF0 (baseline) and SOF2 (progressive) are supported by FJCore
case JPEGMarker.SOF1:
case JPEGMarker.SOF3:
case JPEGMarker.SOF5:
case JPEGMarker.SOF6:
case JPEGMarker.SOF7:
case JPEGMarker.SOF9:
case JPEGMarker.SOF10:
case JPEGMarker.SOF11:
case JPEGMarker.SOF13:
case JPEGMarker.SOF14:
case JPEGMarker.SOF15:
throw new NotSupportedException("Unsupported codec type.");
default: break; // ignore
}
#endregion switch over markers
if (haveMarker)
{
haveMarker = false;
}
else
{
try
{
marker = jpegReader.GetNextMarker();
}
catch (System.IO.EndOfStreamException)
{
break; /* done reading the file */
}
}
}
DecodedJpeg result = new DecodedJpeg(image, headers);
return(result);
}
