/// <param name="matrix">row of black/white values to search
/// </param>
/// <param name="column">x position to start search
/// </param>
/// <param name="row">y position to start search
/// </param>
/// <param name="width">the number of pixels to search on this row
/// </param>
/// <param name="pattern">pattern of counts of number of black and white pixels that are
/// being searched for as a pattern
/// </param>
/// <returns> start/end horizontal offset of guard pattern, as an array of two ints.
/// </returns>
private static int[] findGuardPattern(BitMatrix matrix, int column, int row, int width, bool whiteFirst, int[] pattern)
{
int patternLength = pattern.Length;
// TODO: Find a way to cache this array, as this method is called hundreds of times
// per image, and we want to allocate as seldom as possible.
int[] counters = new int[patternLength];
bool isWhite = whiteFirst;
int counterPosition = 0;
int patternStart = column;
for (int x = column; x < column + width; x++)
{
bool pixel = matrix.get_Renamed(x, row);
if (pixel ^ isWhite)
{
counters[counterPosition]++;
}
else
{
if (counterPosition == patternLength - 1)
{
if (patternMatchVariance(counters, pattern, MAX_INDIVIDUAL_VARIANCE) < MAX_AVG_VARIANCE)
{
return new int[]{patternStart, x};
}
patternStart += counters[0] + counters[1];
for (int y = 2; y < patternLength; y++)
{
counters[y - 2] = counters[y];
}
counters[patternLength - 2] = 0;
counters[patternLength - 1] = 0;
counterPosition--;
}
else
{
counterPosition++;
}
counters[counterPosition] = 1;
isWhite = !isWhite;
}
}
return null;
}
/// <summary> This method detects a Data Matrix code in a "pure" image -- that is, pure monochrome image
/// which contains only an unrotated, unskewed, image of a Data Matrix code, with some white border
/// around it. This is a specialized method that works exceptionally fast in this special
/// case.
/// </summary>
private static BitMatrix extractPureBits(BitMatrix image)
{
// Now need to determine module size in pixels
int height = image.Height;
int width = image.Width;
int minDimension = System.Math.Min(height, width);
// First, skip white border by tracking diagonally from the top left down and to the right:
int borderWidth = 0;
while (borderWidth < minDimension && !image.get_Renamed(borderWidth, borderWidth))
{
borderWidth++;
}
if (borderWidth == minDimension)
{
throw ReaderException.Instance;
}
// And then keep tracking across the top-left black module to determine module size
int moduleEnd = borderWidth + 1;
while (moduleEnd < width && image.get_Renamed(moduleEnd, borderWidth))
{
moduleEnd++;
}
if (moduleEnd == width)
{
throw ReaderException.Instance;
}
int moduleSize = moduleEnd - borderWidth;
// And now find where the bottommost black module on the first column ends
int columnEndOfSymbol = height - 1;
while (columnEndOfSymbol >= 0 && !image.get_Renamed(borderWidth, columnEndOfSymbol))
{
columnEndOfSymbol--;
}
if (columnEndOfSymbol < 0)
{
throw ReaderException.Instance;
}
columnEndOfSymbol++;
// Make sure width of barcode is a multiple of module size
if ((columnEndOfSymbol - borderWidth) % moduleSize != 0)
{
throw ReaderException.Instance;
}
int dimension = (columnEndOfSymbol - borderWidth) / moduleSize;
// Push in the "border" by half the module width so that we start
// sampling in the middle of the module. Just in case the image is a
// little off, this will help recover.
borderWidth += (moduleSize >> 1);
int sampleDimension = borderWidth + (dimension - 1) * moduleSize;
if (sampleDimension >= width || sampleDimension >= height)
{
throw ReaderException.Instance;
}
// Now just read off the bits
BitMatrix bits = new BitMatrix(dimension);
for (int i = 0; i < dimension; i++)
{
int iOffset = borderWidth + i * moduleSize;
for (int j = 0; j < dimension; j++)
{
if (image.get_Renamed(borderWidth + j * moduleSize, iOffset))
{
bits.set_Renamed(j, i);
}
}
}
return bits;
}