private int CalculateScanlineStep(PngColorTypeInformation colorTypeInformation)
{
int scanlineStep = 1;
if (_header.BitDepth >= 8)
{
scanlineStep = (colorTypeInformation.ChannelsPerColor * _header.BitDepth) / 8;
}
return(scanlineStep);
}
private int CalculateScanlineLength(PngColorTypeInformation colorTypeInformation)
{
int scanlineLength = (_header.Width * _header.BitDepth * colorTypeInformation.ChannelsPerColor);
int amount = scanlineLength % 8;
if (amount != 0)
{
scanlineLength += 8 - amount;
}
return(scanlineLength / 8);
}
private void ReadScanlines(MemoryStream dataStream, byte[] pixels, ColorReader colorReader, PngColorTypeInformation colorTypeInformation)
{
dataStream.Position = 0;
int scanlineLength = CalculateScanlineLength(colorTypeInformation);
int scanlineStep = CalculateScanlineStep(colorTypeInformation);
byte[] lastScanline = new byte[scanlineLength];
byte[] currScanline = new byte[scanlineLength];
byte a = 0;
byte b = 0;
byte c = 0;
int row = 0, filter = 0, column = -1;
using (DeflaterInputStream compressedStream = new DeflaterInputStream(dataStream))
{
int readByte = 0;
while ((readByte = compressedStream.ReadByte()) >= 0)
{
if (column == -1)
{
filter = readByte;
column++;
}
else
{
currScanline[column] = (byte)readByte;
if (column >= scanlineStep)
{
a = currScanline[column - scanlineStep];
c = lastScanline[column - scanlineStep];
}
else
{
a = 0;
c = 0;
}
b = lastScanline[column];
if (filter == 1)
{
currScanline[column] = (byte)(currScanline[column] + a);
}
else if (filter == 2)
{
currScanline[column] = (byte)(currScanline[column] + b);
}
else if (filter == 3)
{
currScanline[column] = (byte)(currScanline[column] + (byte)Math.Floor((double)((a + b) / 2)));
}
else if (filter == 4)
{
currScanline[column] = (byte)(currScanline[column] + PaethPredicator(a, b, c));
}
column++;
if (column == scanlineLength)
{
colorReader.ReadScanline(currScanline, pixels, _header);
column = -1;
row++;
Swap(ref currScanline, ref lastScanline);
}
}
}
}
}
/// <summary>
/// Decodes the image from the specified stream and sets
/// the data to image.
/// </summary>
/// <param name="image">The image, where the data should be set to.
/// Cannot be null (Nothing in Visual Basic).</param>
/// <param name="stream">The stream, where the image should be
/// decoded from. Cannot be null (Nothing in Visual Basic).</param>
/// <exception cref="ArgumentNullException">
/// <para><paramref name="image"/> is null (Nothing in Visual Basic).</para>
/// <para>- or -</para>
/// <para><paramref name="stream"/> is null (Nothing in Visual Basic).</para>
/// </exception>
public Image Decode(Stream stream)
{
_stream = stream;
_stream.Seek(8, SeekOrigin.Current);
bool isEndChunckReached = false;
PngChunk currentChunk = null;
byte[] palette = null;
byte[] paletteAlpha = null;
using (MemoryStream dataStream = new MemoryStream())
{
while ((currentChunk = ReadChunk()) != null)
{
if (isEndChunckReached)
{
throw new Exception("Image does not end with end chunk.");
}
if (currentChunk.Type == PngChunkTypes.Header)
{
ReadHeaderChunk(currentChunk.Data);
ValidateHeader();
}
else if (currentChunk.Type == PngChunkTypes.Physical)
{
ReadPhysicalChunk(currentChunk.Data);
}
else if (currentChunk.Type == PngChunkTypes.Data)
{
dataStream.Write(currentChunk.Data, 0, currentChunk.Data.Length);
}
else if (currentChunk.Type == PngChunkTypes.Palette)
{
palette = currentChunk.Data;
}
else if (currentChunk.Type == PngChunkTypes.PaletteAlpha)
{
paletteAlpha = currentChunk.Data;
}
else if (currentChunk.Type == PngChunkTypes.Text)
{
ReadTextChunk(currentChunk.Data);
}
else if (currentChunk.Type == PngChunkTypes.End)
{
isEndChunckReached = true;
}
}
byte[] pixels = new byte[_header.Width * _header.Height * 4];
PngColorTypeInformation colorTypeInformation = _colorTypes[_header.ColorType];
if (colorTypeInformation != null)
{
ColorReader colorReader = colorTypeInformation.CreateColorReader(palette, paletteAlpha);
ReadScanlines(dataStream, pixels, colorReader, colorTypeInformation);
}
Image i = new Image(_header.Width, _header.Height);
int indx = 0;
byte r, g, b, a;
for (uint y = 0; y < i.Height; y++)
{
for (uint x = 0; x < i.Width; x++)
{
r = pixels[indx];
indx++;
g = pixels[indx];
indx++;
b = pixels[indx];
indx++;
a = pixels[indx];
indx++;
i.SetPixel(x, y, new Pixel(r, g, b, a));
}
}
pixels = null;
System.GC.Collect();
return(i);
}
}
