public static Byte[] Decode(Byte[] inp, PdfDictionary prms)
{
if (prms == null)
{
return(inp);
}
var predObj = prms.Get <PdfInteger>("Predictor");
if (predObj == null)
{
return(inp);
}
Int32 predictor = predObj.Value;
if (predictor < 10 && predictor != 2)
{
return(inp);
}
Int32 width = 1;
var colsObj = prms.Get <PdfInteger>("Columns");
if (colsObj != null)
{
width = colsObj.Value;
}
Int32 colors = 1; // TODO from DICT
Int32 bpc = 8; // TODO from DICT
MemoryStream dataStream = new MemoryStream(inp);
MemoryStream fout = new MemoryStream(inp.Length);
Int32 bytesPerPixel = colors * bpc / 8;
Int32 bytesPerRow = (colors * width * bpc + 7) / 8;
Byte[] curr = new Byte[bytesPerRow];
Byte[] prior = new Byte[bytesPerRow];
if (predictor == 2)
{
if (bpc == 8)
{
Int32 numRows = inp.Length / bytesPerRow;
for (Int32 row = 0; row < numRows; row++)
{
Int32 rowStart = row * bytesPerRow;
for (Int32 col = 0 + bytesPerPixel; col < bytesPerRow; col++)
{
inp[rowStart + col] = (Byte)(inp[rowStart + col] + inp[rowStart + col - bytesPerPixel]);
}
}
}
return(inp);
}
// Decode the (sub)image row-by-row
while (true)
{
// Read the filter type byte and a row of data
Int32 filter = 0;
try
{
filter = dataStream.ReadByte();
if (filter < 0)
{
return(fout.ToArray());
}
Int32 tot = 0;
while (tot < bytesPerRow)
{
Int32 n = dataStream.Read(curr, tot, bytesPerRow - tot);
if (n <= 0)
{
return(fout.ToArray());
}
tot += n;
}
}
catch
{
return(fout.ToArray());
}
switch (filter)
{
case 0: //PNG_FILTER_NONE
break;
case 1: //PNG_FILTER_SUB
for (Int32 i = bytesPerPixel; i < bytesPerRow; i++)
{
curr[i] += curr[i - bytesPerPixel];
}
break;
case 2: //PNG_FILTER_UP
for (Int32 i = 0; i < bytesPerRow; i++)
{
curr[i] += prior[i];
}
break;
case 3: //PNG_FILTER_AVERAGE
for (Int32 i = 0; i < bytesPerPixel; i++)
{
curr[i] += (Byte)(prior[i] / 2);
}
for (Int32 i = bytesPerPixel; i < bytesPerRow; i++)
{
curr[i] += (Byte)(((curr[i - bytesPerPixel] & 0xff) + (prior[i] & 0xff)) / 2);
}
break;
case 4: //PNG_FILTER_PAETH
for (Int32 i = 0; i < bytesPerPixel; i++)
{
curr[i] += prior[i];
}
for (Int32 i = bytesPerPixel; i < bytesPerRow; i++)
{
Int32 a = curr[i - bytesPerPixel] & 0xff;
Int32 b = prior[i] & 0xff;
Int32 c = prior[i - bytesPerPixel] & 0xff;
Int32 p = a + b - c;
Int32 pa = Math.Abs(p - a);
Int32 pb = Math.Abs(p - b);
Int32 pc = Math.Abs(p - c);
Int32 ret;
if ((pa <= pb) && (pa <= pc))
{
ret = a;
}
else if (pb <= pc)
{
ret = b;
}
else
{
ret = c;
}
curr[i] += (Byte)(ret);
}
break;
default:
// Error -- uknown filter type
throw new LexerException("png.filter.unknown");
}
fout.Write(curr, 0, curr.Length);
// Swap curr and prior
Byte[] tmp = prior;
prior = curr;
curr = tmp;
}
}
