[Feature request] binarizeEdgePlus #47
Description
Hi @vigri .
/**
* \brief Image binarization using EdgePlus local/global thresholding method.
*
* EdgePlus, zvezdochiot 2023. "Adaptive/global document image binarization".
*/
BinaryImage binarizeEdgePlus(const QImage& src, QSize windowSize, double k = 0.34);BinaryImage binarizeEdgePlus(const QImage& src, const QSize windowSize, const double k) {
if (windowSize.isEmpty()) {
throw std::invalid_argument("binarizeSauvola: invalid windowSize");
}
if (src.isNull()) {
return BinaryImage();
}
QImage gray(toGrayscale(src));
const int w = gray.width();
const int h = gray.height();
IntegralImage<uint32_t> integralImage(w, h);
uint8_t* grayLine = gray.bits();
const int grayBpl = gray.bytesPerLine();
for (int y = 0; y < h; ++y, grayLine += grayBpl) {
integralImage.beginRow();
for (int x = 0; x < w; ++x) {
const uint32_t pixel = grayLine[x];
integralImage.push(pixel);
}
}
const int windowLowerHalf = windowSize.height() >> 1;
const int windowUpperHalf = windowSize.height() - windowLowerHalf;
const int windowLeftHalf = windowSize.width() >> 1;
const int windowRightHalf = windowSize.width() - windowLeftHalf;
grayLine = gray.bits();
for (int y = 0; y < h; ++y) {
const int top = std::max(0, y - windowLowerHalf);
const int bottom = std::min(h, y + windowUpperHalf); // exclusive
for (int x = 0; x < w; ++x) {
const int left = std::max(0, x - windowLeftHalf);
const int right = std::min(w, x + windowRightHalf); // exclusive
const int area = (bottom - top) * (right - left);
assert(area > 0); // because windowSize > 0 and w > 0 and h > 0
const QRect rect(left, top, right - left, bottom - top);
const double windowSum = integralImage.sum(rect);
const double rArea = 1.0 / area;
const double mean = windowSum * rArea;
const double origin = grayLine[x];
// edge = I / blur (shift = -0.5) {0.0 .. >1.0}, mean value = 0.5
const double edge = (origin + 1) / (mean + 1) - 0.5;
// edgeplus = I * edge, mean value = 0.5 * mean(I)
const double edgeplus = origin * edge;
// return k * edgeplus + (1 - k) * I
double retval = k * edgeplus + (1.0 - k) * origin;
// trim value {0..255}
retval = (retval < 0.0) ? 0.0 : (retval < 255.0) ? retval : 255.0;
grayLine[x] = (int)retval;
}
grayLine += grayBpl;
}
return BinaryImage(src, BinaryThreshold::otsuThreshold(gray));
} // binarizeEdgePlusSee also: