samples/cpp/snippets/lsd_lines.cpp

An example using the LineSegmentDetector

Sample output image

#include "opencv2/imgproc.hpp"
#include "opencv2/imgcodecs.hpp"
#include "opencv2/highgui.hpp"
#include <iostream>
 
using namespace std;
using namespace cv;
 
int main(int argc, char** argv)
{
    cv::CommandLineParser parser(argc, argv,
                                 "{input   i|building.jpg|input image}"
                                 "{refine  r|false|if true use LSD_REFINE_STD method, if false use LSD_REFINE_NONE method}"
                                 "{canny   c|false|use Canny edge detector}"
                                 "{overlay o|false|show result on input image}"
                                 "{help    h|false|show help message}");
 
    if (parser.get<bool>("help"))
    {
        parser.printMessage();
        return 0;
    }
 
    parser.printMessage();
 
    String filename = samples::findFile(parser.get<String>("input"));
    bool useRefine = parser.get<bool>("refine");
    bool useCanny = parser.get<bool>("canny");
    bool overlay = parser.get<bool>("overlay");
 
    Mat image = imread(filename, IMREAD_GRAYSCALE);
 
    if( image.empty() )
    {
        cout << "Unable to load " << filename;
        return 1;
    }
 
    imshow("Source Image", image);
 
    if (useCanny)
    {
        Canny(image, image, 50, 200, 3); // Apply Canny edge detector
    }
 
    // Create and LSD detector with standard or no refinement.
    Ptr<LineSegmentDetector> ls = useRefine ? createLineSegmentDetector(LSD_REFINE_STD) : createLineSegmentDetector(LSD_REFINE_NONE);
 
    double start = double(getTickCount());
    vector<Vec4f> lines_std;
 
    // Detect the lines
    ls->detect(image, lines_std);
 
    double duration_ms = (double(getTickCount()) - start) * 1000 / getTickFrequency();
    std::cout << "It took " << duration_ms << " ms." << std::endl;
 
    // Show found lines
    if (!overlay || useCanny)
    {
        image = Scalar(0, 0, 0);
    }
 
    ls->drawSegments(image, lines_std);
 
    String window_name = useRefine ? "Result - standard refinement" : "Result - no refinement";
    window_name += useCanny ? " - Canny edge detector used" : "";
 
    imshow(window_name, image);
 
    waitKey();
    return 0;
}