Opencv学习之 LineSegmentDector(LSD)

简介

这个示例不涉及具体原理，主要演示了如何使用OpenCV对图像进行LSD直线检测。

cv::LineSegmentDetector 类

https://docs.opencv.org/3.4.1/db/d73/classcv_1_1LineSegmentDetector.html#details

Line segment detector class,该类基于论文《Rafael Grompone von Gioi, Jérémie Jakubowicz, Jean-Michel Morel, and Gregory Randall. Lsd: a line segment detector. 2012》 所写。

• 头文件
  #include<opencv2/imgproc.hpp>
• 主要步骤

（1） 使用 createLineSegmentDetector 创建 LSD detector （智能指针）

Ptr<LineSegmentDetector> ls = createLineSegmentDetector(LSD_REFINE_STD); 

（2） 使用 LSD detector 进行LSD直线检测；

vector<Vec4i>lines; // 或vector<Vec4f>lines; 
ls->detect(image,lines);

• image：A grayscale (CV_8UC1) input image. If only a roi needs to be selected, use: lsd_ptr->detect(image(roi), lines, …); lines += Scalar(roi.x, roi.y, roi.x, roi.y);
• lines：A vector of Vec4i or Vec4f elements specifying the beginning and ending point of a line. Where Vec4i/Vec4f is (x1, y1, x2, y2), point 1 is the start, point 2 - end. Returned lines are strictly oriented depending on the gradient.

（3） 使用 drawSegment 在图像中显示找到的直线

// Show found lines
    Mat drawnLines(image); //深拷贝，drawnLines和image位于不同内存
    ls->drawSegments(drawnLines, lines); //lines为上步直线检测的结果

代码地址：https://docs.opencv.org/3.0.0/d8/dd4/lsd_lines_8cpp-example.html

#include <iostream>
#include <string>
 
#include <opencv2/core/core.hpp>
#include <opencv2/core/utility.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/imgcodecs.hpp>
#include <opencv2/highgui/highgui.hpp>
 
using namespace std;
using namespace cv;
 
int main(int argc, char** argv)
{
    std::string in;
    if (argc != 2)
    {
        std::cout << "Usage: lsd_lines [input image]. Now loading .." << std::endl;
        in = "../data/building.jpg";
    }
    else
    {
        in = argv[1];
    }
 
    Mat image = imread(in, IMREAD_GRAYSCALE);
    Mat dst;
 
#if 1
    Canny(image, dst, 50, 200, 3); // Apply canny edge
#endif
 
    // Create and LSD detector with standard or no refinement.
#if 1
    Ptr<LineSegmentDetector> ls = createLineSegmentDetector(LSD_REFINE_STD);
#else
    Ptr<LineSegmentDetector> ls = createLineSegmentDetector(LSD_REFINE_NONE);
#endif
 
    double start = double(getTickCount());
    vector<Vec4f> lines_std;
 
    // Detect the lines
    ls->detect(dst, lines_std);
 
    double duration_ms = (double(getTickCount()) - start) * 1000 / getTickFrequency();
    std::cout << "It took " << duration_ms << " ms." << std::endl;
 
    // Show found lines
    Mat drawnLines(image);
    ls->drawSegments(drawnLines, lines_std);
    imshow("Standard refinement", drawnLines);
 
    waitKey();
    return 0;
}

运行结果：