[Feature request] binarizeEdgePlus

zvezdochiot commented 1 year ago

Hi @4lex4 .

/**
 * \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);
  IntegralImage<uint64_t> integralSqimage(w, h);

  uint8_t* grayLine = gray.bits();
  const int grayBpl = gray.bytesPerLine();

  for (int y = 0; y < h; ++y, grayLine += grayBpl) {
    integralImage.beginRow();
    integralSqimage.beginRow();
    for (int x = 0; x < w; ++x) {
      const uint32_t pixel = grayLine[x];
      integralImage.push(pixel);
      integralSqimage.push(pixel * 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 windowSqsum = integralSqimage.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));
}  // binarizeEdgePlus

4lex4 / scantailor-advanced

[Feature request] binarizeEdgePlus #198