/**
* Detects a Data Matrix Code in an image.
*
* @return {@link DetectorResult} encapsulating results of detecting a Data Matrix Code
* @throws NotFoundException if no Data Matrix Code can be found
*/
public DetectorResult detect() throws NotFoundException {
ResultPoint[] cornerPoints = rectangleDetector.detect();
ResultPoint pointA = cornerPoints[0];
ResultPoint pointB = cornerPoints[1];
ResultPoint pointC = cornerPoints[2];
ResultPoint pointD = cornerPoints[3];
// Point A and D are across the diagonal from one another,
// as are B and C. Figure out which are the solid black lines
// by counting transitions
Vector transitions = new Vector(4);
transitions.addElement(transitionsBetween(pointA, pointB));
transitions.addElement(transitionsBetween(pointA, pointC));
transitions.addElement(transitionsBetween(pointB, pointD));
transitions.addElement(transitionsBetween(pointC, pointD));
Collections.insertionSort(transitions, new ResultPointsAndTransitionsComparator());
// Sort by number of transitions. First two will be the two solid sides; last two
// will be the two alternating black/white sides
ResultPointsAndTransitions lSideOne = (ResultPointsAndTransitions) transitions.elementAt(0);
ResultPointsAndTransitions lSideTwo = (ResultPointsAndTransitions) transitions.elementAt(1);
// Figure out which point is their intersection by tallying up the number of times we see the
// endpoints in the four endpoints. One will show up twice.
Hashtable pointCount = new Hashtable();
increment(pointCount, lSideOne.getFrom());
increment(pointCount, lSideOne.getTo());
increment(pointCount, lSideTwo.getFrom());
increment(pointCount, lSideTwo.getTo());
ResultPoint maybeTopLeft = null;
ResultPoint bottomLeft = null;
ResultPoint maybeBottomRight = null;
Enumeration points = pointCount.keys();
while (points.hasMoreElements()) {
ResultPoint point = (ResultPoint) points.nextElement();
Integer value = (Integer) pointCount.get(point);
if (value.intValue() == 2) {
bottomLeft = point; // this is definitely the bottom left, then -- end of two L sides
} else {
// Otherwise it's either top left or bottom right -- just assign the two arbitrarily now
if (maybeTopLeft == null) {
maybeTopLeft = point;
} else {
maybeBottomRight = point;
}
}
}
if (maybeTopLeft == null || bottomLeft == null || maybeBottomRight == null) {
throw NotFoundException.getNotFoundInstance();
}
// Bottom left is correct but top left and bottom right might be switched
ResultPoint[] corners = {maybeTopLeft, bottomLeft, maybeBottomRight};
// Use the dot product trick to sort them out
ResultPoint.orderBestPatterns(corners);
// Now we know which is which:
ResultPoint bottomRight = corners[0];
bottomLeft = corners[1];
ResultPoint topLeft = corners[2];
// Which point didn't we find in relation to the "L" sides? that's the top right corner
ResultPoint topRight;
if (!pointCount.containsKey(pointA)) {
topRight = pointA;
} else if (!pointCount.containsKey(pointB)) {
topRight = pointB;
} else if (!pointCount.containsKey(pointC)) {
topRight = pointC;
} else {
topRight = pointD;
}
// Next determine the dimension by tracing along the top or right side and counting black/white
// transitions. Since we start inside a black module, we should see a number of transitions
// equal to 1 less than the code dimension. Well, actually 2 less, because we are going to
// end on a black module:
// The top right point is actually the corner of a module, which is one of the two black modules
// adjacent to the white module at the top right. Tracing to that corner from either the top
// left
// or bottom right should work here.
int dimension =
Math.min(
transitionsBetween(topLeft, topRight).getTransitions(),
transitionsBetween(bottomRight, topRight).getTransitions());
if ((dimension & 0x01) == 1) {
// it can't be odd, so, round... up?
dimension++;
}
dimension += 2;
// correct top right point to match the white module
ResultPoint correctedTopRight =
correctTopRight(bottomLeft, bottomRight, topLeft, topRight, dimension);
if (correctedTopRight == null) {
correctedTopRight = topRight;
}
// We redetermine the dimension using the corrected top right point
int dimension2 =
Math.max(
transitionsBetween(topLeft, correctedTopRight).getTransitions(),
transitionsBetween(bottomRight, correctedTopRight).getTransitions());
dimension2++;
if ((dimension2 & 0x01) == 1) {
dimension2++;
}
BitMatrix bits =
sampleGrid(image, topLeft, bottomLeft, bottomRight, correctedTopRight, dimension2);
return new DetectorResult(
bits, new ResultPoint[] {topLeft, bottomLeft, bottomRight, correctedTopRight});
}
/**
* @return the 3 best {@link FinderPattern}s from our list of candidates. The "best" are those
* that have been detected at least {@link #CENTER_QUORUM} times, and whose module size
* differs from the average among those patterns the least
* @throws NotFoundException if 3 such finder patterns do not exist
*/
private FinderPattern[][] selectBestPatterns() throws NotFoundException {
Vector possibleCenters = getPossibleCenters();
int size = possibleCenters.size();
if (size < 3) {
// Couldn't find enough finder patterns
throw NotFoundException.getNotFoundInstance();
}
/*
* Begin HE modifications to safely detect multiple codes of equal size
*/
if (size == 3) {
return new FinderPattern[][] {
new FinderPattern[] {
(FinderPattern) possibleCenters.elementAt(0),
(FinderPattern) possibleCenters.elementAt(1),
(FinderPattern) possibleCenters.elementAt(2)
}
};
}
// Sort by estimated module size to speed up the upcoming checks
Collections.insertionSort(possibleCenters, new ModuleSizeComparator());
/*
* Now lets start: build a list of tuples of three finder locations that
* - feature similar module sizes
* - are placed in a distance so the estimated module count is within the QR specification
* - have similar distance between upper left/right and left top/bottom finder patterns
* - form a triangle with 90° angle (checked by comparing top right/bottom left distance
* with pythagoras)
*
* Note: we allow each point to be used for more than one code region: this might seem
* counterintuitive at first, but the performance penalty is not that big. At this point,
* we cannot make a good quality decision whether the three finders actually represent
* a QR code, or are just by chance layouted so it looks like there might be a QR code there.
* So, if the layout seems right, lets have the decoder try to decode.
*/
Vector results = new Vector(); // holder for the results
for (int i1 = 0; i1 < (size - 2); i1++) {
FinderPattern p1 = (FinderPattern) possibleCenters.elementAt(i1);
if (p1 == null) {
continue;
}
for (int i2 = i1 + 1; i2 < (size - 1); i2++) {
FinderPattern p2 = (FinderPattern) possibleCenters.elementAt(i2);
if (p2 == null) {
continue;
}
// Compare the expected module sizes; if they are really off, skip
float vModSize12 =
(p1.getEstimatedModuleSize() - p2.getEstimatedModuleSize())
/ Math.min(p1.getEstimatedModuleSize(), p2.getEstimatedModuleSize());
float vModSize12A = Math.abs(p1.getEstimatedModuleSize() - p2.getEstimatedModuleSize());
if (vModSize12A > DIFF_MODSIZE_CUTOFF && vModSize12 >= DIFF_MODSIZE_CUTOFF_PERCENT) {
// break, since elements are ordered by the module size deviation there cannot be
// any more interesting elements for the given p1.
break;
}
for (int i3 = i2 + 1; i3 < size; i3++) {
FinderPattern p3 = (FinderPattern) possibleCenters.elementAt(i3);
if (p3 == null) {
continue;
}
// Compare the expected module sizes; if they are really off, skip
float vModSize23 =
(p2.getEstimatedModuleSize() - p3.getEstimatedModuleSize())
/ Math.min(p2.getEstimatedModuleSize(), p3.getEstimatedModuleSize());
float vModSize23A = Math.abs(p2.getEstimatedModuleSize() - p3.getEstimatedModuleSize());
if (vModSize23A > DIFF_MODSIZE_CUTOFF && vModSize23 >= DIFF_MODSIZE_CUTOFF_PERCENT) {
// break, since elements are ordered by the module size deviation there cannot be
// any more interesting elements for the given p1.
break;
}
FinderPattern[] test = {p1, p2, p3};
ResultPoint.orderBestPatterns(test);
// Calculate the distances: a = topleft-bottomleft, b=topleft-topright, c = diagonal
FinderPatternInfo info = new FinderPatternInfo(test);
float dA = ResultPoint.distance(info.getTopLeft(), info.getBottomLeft());
float dC = ResultPoint.distance(info.getTopRight(), info.getBottomLeft());
float dB = ResultPoint.distance(info.getTopLeft(), info.getTopRight());
// Check the sizes
float estimatedModuleCount = (dA + dB) / (p1.getEstimatedModuleSize() * 2.0f);
if (estimatedModuleCount > MAX_MODULE_COUNT_PER_EDGE
|| estimatedModuleCount < MIN_MODULE_COUNT_PER_EDGE) {
continue;
}
// Calculate the difference of the edge lengths in percent
float vABBC = Math.abs((dA - dB) / Math.min(dA, dB));
if (vABBC >= 0.1f) {
continue;
}
// Calculate the diagonal length by assuming a 90° angle at topleft
float dCpy = (float) Math.sqrt(dA * dA + dB * dB);
// Compare to the real distance in %
float vPyC = Math.abs((dC - dCpy) / Math.min(dC, dCpy));
if (vPyC >= 0.1f) {
continue;
}
// All tests passed!
results.addElement(test);
} // end iterate p3
} // end iterate p2
} // end iterate p1
if (!results.isEmpty()) {
FinderPattern[][] resultArray = new FinderPattern[results.size()][];
for (int i = 0; i < results.size(); i++) {
resultArray[i] = (FinderPattern[]) results.elementAt(i);
}
return resultArray;
}
// Nothing found!
throw NotFoundException.getNotFoundInstance();
}
