private bool ApplyChunk(byte[] typeArray, byte[] dataArray)
{
bool result = true;
string typeString = PNGUtil.GetTypeString(typeArray);
switch (typeString)
{
case "IHDR":
result = ApplyChunkIHDR(dataArray);
break;
case "PLTE":
errorMessage = "can't handle PLTE chunk";
result = false;
break;
case "IDAT":
result = ApplyChunkIDAT(dataArray);
break;
case "IEND":
result = ApplyChunkIEND();
foundIEND = result;
break;
case "tRNS":
case "cHRM":
case "gAMA":
case "iCCP":
case "sBIT":
case "sRGB":
case "tEXt":
case "iTXt":
case "zTXt":
case "bKGD":
case "hIST":
case "pHYs":
case "sPLT":
case "tIME":
// chunks to be ignored
break;
default:
errorMessage = "unknown chunk type";
result = false;
break;
}
return(result);
}
private bool ApplyChunkIHDR(byte[] dataArray)
{
// verify length
if (13 != dataArray.Length)
{
return(false);
}
byte[] sizeArray = new byte[4];
Array.Copy(dataArray, 0, sizeArray, 0, 4);
width = PNGUtil.GetInt(sizeArray);
Array.Copy(dataArray, 4, sizeArray, 0, 4);
height = PNGUtil.GetInt(sizeArray);
bitDepth = (int)dataArray[8];
colorType = (int)dataArray[9];
compressMethod = (int)dataArray[10];
filterMethod = (int)dataArray[11];
interlaceMethod = (int)dataArray[12];
if (bitDepth != 8)
{
errorMessage = "can't handle bit depth " + bitDepth;
return(false);
}
if (colorType != 2)
{
errorMessage = "can't handle color type " + colorType;
return(false);
}
if (compressMethod != 0)
{
errorMessage = "strange compress method " + compressMethod;
return(false);
}
if (filterMethod != 0)
{
errorMessage = "strange filter method " + filterMethod;
return(false);
}
if (interlaceMethod < 0 || 1 < interlaceMethod)
{
errorMessage = "strange interlace method " + interlaceMethod;
return(false);
}
return(true);
}
private bool AnalyzeChunk()
{
bool result = true;
int length = 0;
byte[] typeArray = new byte[4];
byte[] temp4Byte = new byte[4];
uint crc = 0;
// length area
Array.Copy(pngData, index, temp4Byte, 0, 4);
length = PNGUtil.GetInt(temp4Byte);
index += 4;
// type area
Array.Copy(pngData, index, typeArray, 0, 4);
index += 4;
// data area
byte[] dataArray = new byte[length];
Array.Copy(pngData, index, dataArray, 0, length);
index += length;
// CRC area
Array.Copy(pngData, index, temp4Byte, 0, 4);
index += 4;
crc = (uint)PNGUtil.GetInt(temp4Byte);
// CRC check
if (CRCChecker.CRC(typeArray, dataArray) == crc)
{
result = ApplyChunk(typeArray, dataArray);
}
else
{
// CRC invalid
errorMessage = "CRC invalid";
result = false;
}
return(result);
}
public bool Decode()
{
PNGAnalyzer analyzer = new PNGAnalyzer(pngData);
if (!analyzer.Analyze())
{
errorMessage = analyzer.ErrorMessage;
return(false);
}
// succeeded to scan data
// ======================
// begin to arrange the image data
height = analyzer.Height;
width = analyzer.Width;
dataR = new byte[height * width];
dataG = new byte[height * width];
dataB = new byte[height * width];
colorType = analyzer.ColorType;
switch (colorType)
{
case 2:
channels = 3;
break;
default:
errorMessage = "Color type can't be handled";
return(false);
}
decompressedData = analyzer.DecompressData;
passTotal = analyzer.InterlaceMethod == 0 ? 1 : 7;
for (int passIndex = 0; passIndex < passTotal; passIndex++)
{
int heightStart = 0;
int heightSkip = 1;
int widthStart = 0;
int widthSkip = 1;
int rowLength = width;
// for interlace,
if (passTotal > 1)
{
widthStart = PNGUtil.passStart[passIndex];
widthSkip = PNGUtil.passIncrement[passIndex];
heightStart = PNGUtil.passYStart[passIndex];
heightSkip = PNGUtil.passYIncrement[passIndex];
rowLength = PNGUtil.CalculateWidth(width, passIndex);
}
// in the case that the pass have no reduced image.
if (rowLength <= 0)
{
continue;
}
int rowBytes = rowLength * channels + 1;
byte[] rowPrev;
byte[] rowCurrent = new byte[rowBytes];
for (int h = heightStart; h < height; h += heightSkip)
{
rowPrev = rowCurrent;
rowCurrent = new byte[rowBytes];
Array.Copy(decompressedData, decompressedIndex, rowCurrent, 0, rowBytes);
switch (rowCurrent[0])
{
case 0:
// NONE
break;
case 1:
// SUB
for (int i = 4; i < rowBytes; i += 3)
{
rowCurrent[i + 0] = (byte)((int)rowCurrent[i + 0] + (int)rowCurrent[i - 3]);
rowCurrent[i + 1] = (byte)((int)rowCurrent[i + 1] + (int)rowCurrent[i - 2]);
rowCurrent[i + 2] = (byte)((int)rowCurrent[i + 2] + (int)rowCurrent[i - 1]);
}
break;
case 2:
// UP
for (int i = 1; i < rowBytes; i += 3)
{
rowCurrent[i + 0] = (byte)((int)rowCurrent[i + 0] + (int)rowPrev[i + 0]);
rowCurrent[i + 1] = (byte)((int)rowCurrent[i + 1] + (int)rowPrev[i + 1]);
rowCurrent[i + 2] = (byte)((int)rowCurrent[i + 2] + (int)rowPrev[i + 2]);
}
break;
case 3:
// AVERAGE
rowCurrent[1] = (byte)((int)rowCurrent[1] + ((int)rowPrev[1] / 2));
rowCurrent[2] = (byte)((int)rowCurrent[2] + ((int)rowPrev[2] / 2));
rowCurrent[3] = (byte)((int)rowCurrent[3] + ((int)rowPrev[3] / 2));
for (int i = 4; i < rowBytes; i += 3)
{
rowCurrent[i + 0] = (byte)((int)rowCurrent[i + 0] + (((int)rowCurrent[i - 3] + (int)rowPrev[i + 0]) / 2));
rowCurrent[i + 1] = (byte)((int)rowCurrent[i + 1] + (((int)rowCurrent[i - 2] + (int)rowPrev[i + 1]) / 2));
rowCurrent[i + 2] = (byte)((int)rowCurrent[i + 2] + (((int)rowCurrent[i - 1] + (int)rowPrev[i + 2]) / 2));
}
break;
case 4:
// PAETH
rowCurrent[1] = (byte)((int)rowCurrent[1] + PNGUtil.PaethPredictor(0, (int)rowPrev[1], 0));
rowCurrent[2] = (byte)((int)rowCurrent[2] + PNGUtil.PaethPredictor(0, (int)rowPrev[2], 0));
rowCurrent[3] = (byte)((int)rowCurrent[3] + PNGUtil.PaethPredictor(0, (int)rowPrev[3], 0));
for (int i = 4; i < rowBytes; i += 3)
{
rowCurrent[i + 0] = (byte)((int)rowCurrent[i + 0] + PNGUtil.PaethPredictor((int)rowCurrent[i - 3], (int)rowPrev[i + 0], (int)rowPrev[i - 3]));
rowCurrent[i + 1] = (byte)((int)rowCurrent[i + 1] + PNGUtil.PaethPredictor((int)rowCurrent[i - 2], (int)rowPrev[i + 1], (int)rowPrev[i - 2]));
rowCurrent[i + 2] = (byte)((int)rowCurrent[i + 2] + PNGUtil.PaethPredictor((int)rowCurrent[i - 1], (int)rowPrev[i + 2], (int)rowPrev[i - 1]));
}
break;
default:
errorMessage = "Unknown filter type";
return(false);
}
int t = 1;
for (int w = widthStart; w < width; w += widthSkip)
{
dataR[h * width + w] = rowCurrent[t++];
dataG[h * width + w] = rowCurrent[t++];
dataB[h * width + w] = rowCurrent[t++];
}
decompressedIndex += rowBytes;
}
}
return(true);
}