/// <summary>
/// Gets the closest decoded value.
/// </summary>
/// <returns>The closest decoded value.</returns>
/// <param name="moduleBitCount">Module bit count.</param>
private static int GetClosestDecodedValue(int[] moduleBitCount)
{
int bitCountSum = PDF417Common.GetBitCountSum(moduleBitCount);
float[] bitCountRatios = new float[PDF417Common.BARS_IN_MODULE];
for (int i = 0; i < bitCountRatios.Length; i++)
{
bitCountRatios[i] = moduleBitCount[i] / (float)bitCountSum;
}
float bestMatchError = float.MaxValue;
int bestMatch = PDF417Common.INVALID_CODEWORD;
for (int j = 0; j < RATIOS_TABLE.Length; j++)
{
float error = 0.0f;
for (int k = 0; k < PDF417Common.BARS_IN_MODULE; k++)
{
float diff = RATIOS_TABLE[j][k] - bitCountRatios[k];
error += diff * diff;
}
if (error < bestMatchError)
{
bestMatchError = error;
bestMatch = PDF417Common.SYMBOL_TABLE[j];
}
}
return(bestMatch);
}
/// <summary>
/// Samples the bit counts.
/// </summary>
/// <returns>The bit counts.</returns>
/// <param name="moduleBitCount">Module bit count.</param>
private static int[] SampleBitCounts(int[] moduleBitCount)
{
float bitCountSum = PDF417Common.GetBitCountSum(moduleBitCount);
int[] result = new int[PDF417Common.BARS_IN_MODULE];
int bitCountIndex = 0;
int sumPreviousBits = 0;
for (int i = 0; i < PDF417Common.MODULES_IN_CODEWORD; i++)
{
float sampleIndex =
bitCountSum / (2 * PDF417Common.MODULES_IN_CODEWORD) +
(i * bitCountSum) / PDF417Common.MODULES_IN_CODEWORD;
if (sumPreviousBits + moduleBitCount[bitCountIndex] <= sampleIndex)
{
sumPreviousBits += moduleBitCount[bitCountIndex];
bitCountIndex++;
}
result[bitCountIndex]++;
}
return(result);
}
/// <summary>
/// Detects the codeword.
/// </summary>
/// <returns>The codeword.</returns>
/// <param name="image">Image.</param>
/// <param name="minColumn">Minimum column.</param>
/// <param name="maxColumn">Max column.</param>
/// <param name="leftToRight">If set to <c>true</c> left to right.</param>
/// <param name="startColumn">Start column.</param>
/// <param name="imageRow">Image row.</param>
/// <param name="minCodewordWidth">Minimum codeword width.</param>
/// <param name="maxCodewordWidth">Max codeword width.</param>
private static Codeword DetectCodeword(BitMatrix image,
int minColumn,
int maxColumn,
bool leftToRight,
int startColumn,
int imageRow,
int minCodewordWidth,
int maxCodewordWidth)
{
startColumn = AdjustCodewordStartColumn(image, minColumn, maxColumn, leftToRight, startColumn, imageRow);
// we usually know fairly exact now how long a codeword is. We should provide minimum and maximum expected Length
// and try to adjust the read pixels, e.g. remove single pixel errors or try to cut off exceeding pixels.
// min and maxCodewordWidth should not be used as they are calculated for the whole barcode an can be inaccurate
// for the current position
int[] moduleBitCount = GetModuleBitCount(image, minColumn, maxColumn, leftToRight, startColumn, imageRow);
if (moduleBitCount == null)
{
return(null);
}
int endColumn;
int codewordBitCount = PDF417Common.GetBitCountSum(moduleBitCount);
if (leftToRight)
{
endColumn = startColumn + codewordBitCount;
}
else
{
for (int i = 0; i < moduleBitCount.Length >> 1; i++)
{
int tmpCount = moduleBitCount[i];
moduleBitCount[i] = moduleBitCount[moduleBitCount.Length - 1 - i];
moduleBitCount[moduleBitCount.Length - 1 - i] = tmpCount;
}
endColumn = startColumn;
startColumn = endColumn - codewordBitCount;
}
// TODO implement check for width and correction of black and white bars
// use start (and maybe stop pattern) to determine if blackbars are wider than white bars. If so, adjust.
// should probably done only for codewords with a lot more than 17 bits.
// The following fixes 10-1.png, which has wide black bars and small white bars
// for (int i = 0; i < moduleBitCount.Length; i++) {
// if (i % 2 == 0) {
// moduleBitCount[i]--;
// } else {
// moduleBitCount[i]++;
// }
// }
// We could also use the width of surrounding codewords for more accurate results, but this seems
// sufficient for now
if (!CheckCodewordSkew(codewordBitCount, minCodewordWidth, maxCodewordWidth))
{
// We could try to use the startX and endX position of the codeword in the same column in the previous row,
// create the bit count from it and normalize it to 8. This would help with single pixel errors.
return(null);
}
int decodedValue = PDF417CodewordDecoder.GetDecodedValue(moduleBitCount);
int codeword = PDF417Common.GetCodeword(decodedValue);
if (codeword == -1)
{
return(null);
}
return(new Codeword(startColumn, endColumn, GetCodewordBucketNumber(decodedValue), codeword));
}