/// <summary>
/// Embeds a given watermark into a PNG file and saves the result.
/// </summary>
/// <param name="file">PNGFile to use in the watermarking process.</param>
/// <param name="mark">The watermark to embed.</param>
/// <param name="password">A password for the embedding process</param>
/// <param name="outputPath">Location of the saved file.</param>
public static void EmbedWatermark(PNGFile file, Watermark mark, string password, string outputPath)
{
Rfc2898DeriveBytes bytes = new Rfc2898DeriveBytes(password, new byte[] { 112, 52, 63, 42, 180, 121, 53, 27 }, 1000);
PNGScrambler scrambler = new PNGScrambler(file, bytes.GetBytes(16), bytes.GetBytes(8));
byte[] markBytes = mark.GetBytes();
if (ReedSolomonProtection == false)
{
EmbedData(markBytes, scrambler);
}
else
{
markBytes = EncodeWithReedSolomon(markBytes);
EmbedData(markBytes, scrambler);
}
file.SaveAs(outputPath);
}
private static byte[] ReadBytes(PNGFile file, PNGScrambler scrambler, int count, int skip = 0)
{
scrambler.Reset();
List <byte> bits = new List <byte>();
int numBitsToRead = count * 8;
int pixelsToRead = numBitsToRead / 6 + ((numBitsToRead / 6.0) % 1.0 != 0 ? 1 : 0);
int pixelsToSkip = (skip * 8) / 6;
//int bitPairsToThrowaway = pixelsToSkip == 0 ? 0 : (6 - ((skip * 8) % 6)) / 2;
int bitPairsToThrowaway = ((skip * 8) % 6) / 2;
if (bitPairsToThrowaway == 2)
{
pixelsToRead++;
}
for (var x = 0; x < pixelsToSkip; x++)
{
scrambler.GetPixel();
}
for (var x = 0; x < pixelsToRead; x++)
{
PNGPixel p = scrambler.GetPixel();
bits.Add((byte)(p.Red & 0x03));
bits.Add((byte)(p.Green & 0x03));
bits.Add((byte)(p.Blue & 0x03));
}
for (var x = 0; x < bitPairsToThrowaway; x++)
{
bits.RemoveAt(0);
}
return(BitsToBytes(bits));
}
/// <summary>
/// Extracts a stored watermark from a PNGFile.
/// </summary>
/// <param name="file">PNGFile that contains the watermark.</param>
/// <param name="mark">An empty watermark that will be populated.</param>
/// <param name="password">Password that was used to embed the watermark.</param>
/// <returns></returns>
public static Watermark ExtractWatermark(PNGFile file, string password)
{
Rfc2898DeriveBytes bytes = new Rfc2898DeriveBytes(password, new byte[] { 112, 52, 63, 42, 180, 121, 53, 27 }, 1000);
PNGScrambler scrambler = new PNGScrambler(file, bytes.GetBytes(16), bytes.GetBytes(8));
byte[] data = null;
byte markType;
if (ReedSolomonProtection == false)
{
byte[] type = ReadBytes(file, scrambler, 1);
markType = type[0];
if (markType > 9)
{
return(null);
}
byte[] dword = ReadBytes(file, scrambler, 4, 1);
int length = BitConverter.ToInt32(dword, 0);
try
{
data = ReadBytes(file, scrambler, length, 5);
}
catch (Exception e) { return(null); }
}
else
{
byte[] rsType = ReadBytes(file, scrambler, 3, 0);
byte[] type = correctErrors(rsType, 1);
markType = type[0];
if ((markType & 0x80) != 0x80)
{
return(null);
}
markType ^= 0x80;
byte[] rsLength = ReadBytes(file, scrambler, 12, 3);
byte[] length = correctErrors(rsLength, 4);
int markLength = BitConverter.ToInt32(length, 0);
int position = 0;
int numBlocks = (markLength / 256) + (markLength % 256 > 0 ? 1 : 0);
MemoryStream msOut = new MemoryStream();
while (numBlocks > 0)
{
int bytesInBlock = (markLength - (position / 2) < 256 ? markLength - (position / 2) : 256);
bytesInBlock *= 2;
byte[] codeBytes = ReadBytes(file, scrambler, bytesInBlock, position + 15);
byte[] fixedData = correctErrors(codeBytes, bytesInBlock / 2);
msOut.Write(fixedData, 0, fixedData.Length);
numBlocks--;
position += bytesInBlock;
}
data = msOut.ToArray();
}
Watermark mark = null;
switch (markType)
{
case 1:
mark = TextWatermark.LoadFromBytes(data);
break;
case 2:
mark = FileWatermark.LoadFromBytes(data);
break;
case 3:
mark = BinaryWatermark.LoadFromBytes(data);
break;
case 4:
mark = CompositeWatermark.LoadFromBytes(data);
break;
case 9:
mark = EncryptedWatermark.LoadFromBytes(data);
break;
}
return(mark);
}
