Question

我试图在OpenCV中对输入图像执行方向估计。我使用sobel函数来获取图像的渐变，并使用另一个名为calculateOrientations的函数（我在互联网上找到）来计算方向。

代码如下：

void computeGradient(cv::Mat inputImg)
{
    // Gradient X
    cv::Sobel(inputImg, grad_x, CV_16S, 1, 0, 5, 1, 0, cv::BORDER_DEFAULT);
    cv::convertScaleAbs(grad_x, abs_grad_x);

    // Gradient Y
    cv::Sobel(inputImg, grad_y, CV_16S, 0, 1, 5, 1, 0, cv::BORDER_DEFAULT);
    cv::convertScaleAbs(grad_y, abs_grad_y);

    // convert from CV_8U to CV_32F
    abs_grad_x.convertTo(abs_grad_x2, CV_32F, 1. / 255);
    abs_grad_y.convertTo(abs_grad_y2, CV_32F, 1. / 255);

    // calculate orientations
    calculateOrientations(abs_grad_x2, abs_grad_y2);    
} 

void calculateOrientations(cv::Mat gradientX, cv::Mat gradientY)
{
    // Create container element
    orientation = cv::Mat(gradientX.rows, gradientX.cols, CV_32F);

    // Calculate orientations of gradients --> in degrees
    // Loop over all matrix values and calculate the accompagnied orientation
    for (int i = 0; i < gradientX.rows; i++){
        for (int j = 0; j < gradientX.cols; j++){
            // Retrieve a single value
            float valueX = gradientX.at<float>(i, j);
            float valueY = gradientY.at<float>(i, j);
            // Calculate the corresponding single direction, done by applying the arctangens function
            float result = cv::fastAtan2(valueX, valueY);
            // Store in orientation matrix element
            orientation.at<float>(i, j) = result;
        }
    }
}

现在，我需要确定获得的方向是否正确。为此，我想在方向矩阵上为每个大小为5x5的块绘制箭头。有人可以建议我如何绘制箭头吗？谢谢。

Answer 1

OpenCV区分方向的最简单方法是在线的起点或终点绘制小圆或方形。箭头afaik没有功能。如果你需要箭头，你必须写这个（这很简单，但也需要时间）。一旦我这样做了（不是openCV，但我希望你转换它）：

  double arrow_pos = 0.5; // 0.5 = at the center of line
  double len = sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));
  double co = (x2-x1)/len, si = (y2-y1)/len; // line coordinates are (x1,y1)-(x2,y2)
  double const l = 15, sz = linewidth*2; // l - arrow length 
  double x0 = x2 - len*arrow_pos*co;
  double y0 = y2 - len*arrow_pos*si;
  double x = x2 - (l+len*arrow_pos)*co;
  double y = y2 - (l+len*arrow_pos)*si;
  TPoint tp[4] = {TPoint(x+sz*si, y-sz*co), TPoint(x0, y0), TPoint(x-sz*si, y+sz*co), TPoint(x+l*0.3*co, y+0.3*l*si)};
  Polygon(tp, 3);
  Canvas->Polyline(tp, 2);

更新：自OpenCV 2.4.10和3.0

以来添加了arrowedLine（...）函数

opencv：如何在方向图上绘制箭头

1 个答案: