private byte[] ReadChunkType(PngChunk chunk)
{
byte[] typeBuffer = new byte[4];
int numBytes = _stream.Read(typeBuffer, 0, 4);
if (numBytes >= 1 && numBytes <= 3)
{
throw new ImageFormatException("Image stream is not valid!");
}
char[] chars = new char[4];
chars[0] = (char)typeBuffer[0];
chars[1] = (char)typeBuffer[1];
chars[2] = (char)typeBuffer[2];
chars[3] = (char)typeBuffer[3];
chunk.Type = new string(chars);
return(typeBuffer);
}
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 ImageFormatException("Image does not end with end chunk.");
}
if (currentChunk.Type == PngChunkTypes.Header)
{
ReadHeaderChunk(currentChunk.Data);
ValidateHeader();
}
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.End)
{
isEndChunckReached = true;
}
}
if (_header.Width > Image.MaxWidth || _header.Height > Image.MaxHeight)
{
throw new ArgumentOutOfRangeException(
$"The input png '{ _header.Width }x{ _header.Height }' is bigger then the max allowed size '{ Image.MaxWidth }x{ Image.MaxHeight }'");
}
byte[] pixels = new byte[_header.Width * _header.Height * 4];
PngColorTypeInformation colorTypeInformation = _colorTypes[_header.ColorType];
if (colorTypeInformation != null)
{
IColorReader colorReader = colorTypeInformation.CreateColorReader(palette, paletteAlpha);
ReadScanlines(dataStream, pixels, colorReader, colorTypeInformation);
}
return(new Image(_header.Width, _header.Height, pixels));
}
}
private int ReadChunkLength(PngChunk chunk)
{
byte[] lengthBuffer = new byte[4];
int numBytes = _stream.Read(lengthBuffer, 0, 4);
if (numBytes >= 1 && numBytes <= 3)
{
throw new ImageFormatException("Image stream is not valid!");
}
Array.Reverse(lengthBuffer);
chunk.Length = BitConverter.ToInt32(lengthBuffer, 0);
return numBytes;
}
private byte[] ReadChunkType(PngChunk chunk)
{
byte[] typeBuffer = new byte[4];
int numBytes = _stream.Read(typeBuffer, 0, 4);
if (numBytes >= 1 && numBytes <= 3)
{
throw new ImageFormatException("Image stream is not valid!");
}
char[] chars = new char[4];
chars[0] = (char)typeBuffer[0];
chars[1] = (char)typeBuffer[1];
chars[2] = (char)typeBuffer[2];
chars[3] = (char)typeBuffer[3];
chunk.Type = new string(chars);
return typeBuffer;
}
private void ReadChunkData(PngChunk chunk)
{
if (chunk.Length > MaxChunkSize)
{
throw new ArgumentOutOfRangeException($"Png chunk size '{ chunk.Length }' excceeds the '{ MaxChunkSize }'");
}
chunk.Data = new byte[chunk.Length];
_stream.Read(chunk.Data, 0, chunk.Length);
}
private void ReadChunkCrc(PngChunk chunk, byte[] typeBuffer)
{
byte[] crcBuffer = new byte[4];
int numBytes = _stream.Read(crcBuffer, 0, 4);
if (numBytes >= 1 && numBytes <= 3)
{
throw new ImageFormatException("Image stream is not valid!");
}
Array.Reverse(crcBuffer);
chunk.Crc = BitConverter.ToUInt32(crcBuffer, 0);
Crc32 crc = new Crc32();
crc.Update(typeBuffer);
crc.Update(chunk.Data);
if (crc.Value != chunk.Crc)
{
throw new ImageFormatException("CRC Error. PNG Image chunk is corrupt!");
}
}
private PngChunk ReadChunk()
{
PngChunk chunk = new PngChunk();
if (ReadChunkLength(chunk) == 0)
{
return null;
}
byte[] typeBuffer = ReadChunkType(chunk);
ReadChunkData(chunk);
ReadChunkCrc(chunk, typeBuffer);
return chunk;
}
