SegmentList WaterShedDecomposer::watershed(ImageGray const & gradient,
ImageColor const & image) const {
SegmentList segments;
std::unique_ptr<int[]> labels(new int[image.area()]);
for (int i=0; i<image.area(); ++i) labels[i] = -1;
int offsets[]{-image.width(), -1, 1, image.width()};
QList<GradPixelRef> queue;
for (int i=0; i<gradient.area(); ++i) {
queue << GradPixelRef{gradient.at(i).l, i};
}
std::sort(queue.begin(), queue.end(), lessThan);
int label;
int lastLabel = -1;
int i, j;
QList<int> neighLbls;
Pixel * pixel;
Segment * segment;
foreach (GradPixelRef const & gradPix, queue) {
i = gradPix.index;
pixel = new Pixel(Position(i%image.width(), i/image.width()), image.at(i));
// gather neighbours
neighLbls.clear();
for (int o=0; o<4; ++o) {
j = i + offsets[o];
if (image.areNeighbours(i, j) && labels[j] > -1 && !neighLbls.contains(labels[j])) {
neighLbls << labels[j];
}
}
// treat pixel according to neighbour count
switch (neighLbls.size()) {
case 0: // new marker
labels[i] = ++lastLabel;
segment = new Segment();
segment->addPixel(pixel);
segments << segment;
break;
case 1: // add to basin
label = neighLbls.first();
labels[i] = label;
segments.at(label)->addPixel(pixel);
break;
default: // new watershed
// add pixel the segment of the nearest neighbour in color
double distMin = std::numeric_limits<double>::max();
double dist;
int jMin = 0;
for (int o=0; o<4; ++o) {
j = i + offsets[o];
if (image.areNeighbours(i, j) && labels[j] > -1) {
dist = (image.at(i)-image.at(j)).magnitudeSquared();
if (dist < distMin) {
distMin = dist;
jMin = j;
}
}
}
labels[i] = labels[jMin];
segments.at(labels[jMin])->addPixel(pixel);
// beneighbour the segments
for (int k=0; k<neighLbls.count()-1; ++k) {
for (int l=k+1; l<neighLbls.count(); ++l) {
segments.at(neighLbls.at(k))->addNeighbour(segments.at(neighLbls.at(l)));
segments.at(neighLbls.at(l))->addNeighbour(segments.at(neighLbls.at(k)));
}
}
break;
}
}
