OpenCV线路检测

Question

我试图在此图像中找到居中框的边缘:

我尝试使用houghLines使用dRho = img_width/1000,dTheta = pi/180,阈值= 250它在这个图像上效果很好,缩放到大小的1/3,但在全尺寸图像上它只是到处都是线条在各个方向......

我可以做些什么来调整这个更准确？

Answer 1

实现以下结果的代码稍微修改了本答案中提供的代码:如何检测方块:

原始程序可以在OpenCV中找到,它叫做squares.cpp.下面的代码被修改为仅在第一个颜色平面中搜索正方形,但由于它仍然检测到许多正方形,所以在程序结束时我将丢弃除第一个之外的所有正方形,然后调用draw_squares()以显示检测到的内容.你可以更容易地改变它以绘制所有这些并查看检测到的所有内容.

你可以从现在开始做各种各样的事情,包括设置一个感兴趣的(ROI)区域来提取广场内的区域(忽略它周围的一切).

您可以看到检测到的矩形与图像中的线条不完全对齐.您应该在图像中执行一些预处理(侵蚀？)操作,以减少线条的粗细并改善检测.但是从这里开始就是你的全部内容:

#include <cv.h>
#include <highgui.h>

using namespace cv;

double angle( cv::Point pt1, cv::Point pt2, cv::Point pt0 ) {
    double dx1 = pt1.x - pt0.x;
    double dy1 = pt1.y - pt0.y;
    double dx2 = pt2.x - pt0.x;
    double dy2 = pt2.y - pt0.y;
    return (dx1*dx2 + dy1*dy2)/sqrt((dx1*dx1 + dy1*dy1)*(dx2*dx2 + dy2*dy2) + 1e-10);
}

void find_squares(Mat& image, vector<vector<Point> >& squares)
{
    // TODO: pre-processing

    // blur will enhance edge detection
    Mat blurred(image);
    medianBlur(image, blurred, 9);

    Mat gray0(blurred.size(), CV_8U), gray;
    vector<vector<Point> > contours;

    // find squares in the first color plane.
    for (int c = 0; c < 1; c++)
    {
        int ch[] = {c, 0};
        mixChannels(&blurred, 1, &gray0, 1, ch, 1);

        // try several threshold levels
        const int threshold_level = 2;
        for (int l = 0; l < threshold_level; l++)
        {
            // Use Canny instead of zero threshold level!
            // Canny helps to catch squares with gradient shading
            if (l == 0)
            {
                Canny(gray0, gray, 10, 20, 3); // 

                // Dilate helps to remove potential holes between edge segments
                dilate(gray, gray, Mat(), Point(-1,-1));
            }
            else
            {
                    gray = gray0 >= (l+1) * 255 / threshold_level;
            }

            // Find contours and store them in a list
            findContours(gray, contours, CV_RETR_LIST, CV_CHAIN_APPROX_SIMPLE);

            // Test contours
            vector<Point> approx;
            for (size_t i = 0; i < contours.size(); i++)
            {
                    // approximate contour with accuracy proportional
                    // to the contour perimeter
                    approxPolyDP(Mat(contours[i]), approx, arcLength(Mat(contours[i]), true)*0.02, true);

                    // Note: absolute value of an area is used because
                    // area may be positive or negative - in accordance with the
                    // contour orientation
                    if (approx.size() == 4 &&
                            fabs(contourArea(Mat(approx))) > 1000 &&
                            isContourConvex(Mat(approx)))
                    {
                            double maxCosine = 0;

                            for (int j = 2; j < 5; j++)
                            {
                                    double cosine = fabs(angle(approx[j%4], approx[j-2], approx[j-1]));
                                    maxCosine = MAX(maxCosine, cosine);
                            }

                            if (maxCosine < 0.3)
                                    squares.push_back(approx);
                    }
            }
        }
    }
}

void draw_squares(Mat& img, vector<vector<Point> > squares)
{
    for (int i = 0; i < squares.size(); i++)
    {
        for (int j = 0; j < squares[i].size(); j++)
        {
            cv::line(img, squares[i][j], squares[i][(j+1) % 4], cv::Scalar(0, 255, 0), 1, CV_AA);
        }
    }
}


int main(int argc, char* argv[])
{
    Mat img = imread(argv[1]);

    vector<vector<Point> > squares;
    find_squares(img, squares);

    std::cout << "* " << squares.size() << " squares were found." << std::endl;

    // Ignore all the detected squares and draw just the first found
    vector<vector<Point> > tmp;
    if (squares.size() > 0)
    {
        tmp.push_back(squares[0]);
        draw_squares(img, tmp);
    }
    //imshow("squares", img);
    //cvWaitKey(0);

    imwrite("out.png", img);

    return 0;
}