cv::ximgproc::FastLineDetector Class Reference

Class implementing the FLD (Fast Line Detector) algorithm described in. More...

#include <opencv2/ximgproc/fast_line_detector.hpp>

Inheritance diagram for cv::ximgproc::FastLineDetector:

Public Member Functions
virtual	~FastLineDetector ()
virtual void	detect (InputArray _image, OutputArray _lines)=0
	Finds lines in the input image. This is the output of the default parameters of the algorithm on the above shown image.
virtual void	drawSegments (InputOutputArray _image, InputArray lines, bool draw_arrow=false)=0
	Draws the line segments on a given image.
Public Member Functions inherited from cv::Algorithm
	Algorithm ()
virtual	~Algorithm ()
virtual void	clear ()
	Clears the algorithm state.
virtual bool	empty () const
	Returns true if the Algorithm is empty (e.g. in the very beginning or after unsuccessful read.
virtual String	getDefaultName () const
virtual void	read (const FileNode &fn)
	Reads algorithm parameters from a file storage.
virtual void	save (const String &filename) const
virtual void	write (FileStorage &fs) const
	Stores algorithm parameters in a file storage.
void	write (const Ptr< FileStorage > &fs, const String &name=String()) const
	simplified API for language bindingsThis is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Additional Inherited Members
Static Public Member Functions inherited from cv::Algorithm
template<typename _Tp >
static Ptr< _Tp >	load (const String &filename, const String &objname=String())
	Loads algorithm from the file.
template<typename _Tp >
static Ptr< _Tp >	loadFromString (const String &strModel, const String &objname=String())
	Loads algorithm from a String.
template<typename _Tp >
static Ptr< _Tp >	read (const FileNode &fn)
	Reads algorithm from the file node.
Protected Member Functions inherited from cv::Algorithm
void	writeFormat (FileStorage &fs) const

Detailed Description

Class implementing the FLD (Fast Line Detector) algorithm described in.

Lee14 .

#include <iostream>

#include "opencv2/imgproc.hpp"
#include "opencv2/ximgproc.hpp"
#include "opencv2/imgcodecs.hpp"
#include "opencv2/highgui.hpp"

using namespace std;
using namespace cv;
using namespace cv::ximgproc;

int main(int argc, char** argv)
{
    std::string in;
    cv::CommandLineParser parser(argc, argv, "{@input|../samples/data/corridor.jpg|input image}{help h||show help message}");
    if (parser.has("help"))
    {
        parser.printMessage();
        return 0;
    }
    in = parser.get<string>("@input");

    Mat image = imread(in, IMREAD_GRAYSCALE);

    if( image.empty() )
    {
        return -1;
    }

    // Create LSD detector
    Ptr<LineSegmentDetector> lsd = createLineSegmentDetector();
    vector<Vec4f> lines_lsd;

    // Create FLD detector
    // Param               Default value   Description
    // length_threshold    10            - Segments shorter than this will be discarded
    // distance_threshold  1.41421356    - A point placed from a hypothesis line
    //                                     segment farther than this will be
    //                                     regarded as an outlier
    // canny_th1           50            - First threshold for
    //                                     hysteresis procedure in Canny()
    // canny_th2           50            - Second threshold for
    //                                     hysteresis procedure in Canny()
    // canny_aperture_size 3             - Aperturesize for the sobel
    //                                     operator in Canny()
    // do_merge            false         - If true, incremental merging of segments
    //                                     will be perfomred
    int length_threshold = 10;
    float distance_threshold = 1.41421356f;
    double canny_th1 = 50.0;
    double canny_th2 = 50.0;
    int canny_aperture_size = 3;
    bool do_merge = false;
    Ptr<FastLineDetector> fld = createFastLineDetector(length_threshold,
            distance_threshold, canny_th1, canny_th2, canny_aperture_size,
            do_merge);
    vector<Vec4f> lines_fld;

    // Because of some CPU's power strategy, it seems that the first running of
    // an algorithm takes much longer. So here we run both of the algorithmes 10
    // times to see each algorithm's processing time with sufficiently warmed-up
    // CPU performance.
    for(int run_count = 0; run_count < 10; run_count++) {
        lines_lsd.clear();
        int64 start_lsd = getTickCount();
        lsd->detect(image, lines_lsd);
        // Detect the lines with LSD
        double freq = getTickFrequency();
        double duration_ms_lsd = double(getTickCount() - start_lsd) * 1000 / freq;
        std::cout << "Elapsed time for LSD: " << duration_ms_lsd << " ms." << std::endl;

        lines_fld.clear();
        int64 start = getTickCount();
        // Detect the lines with FLD
        fld->detect(image, lines_fld);
        double duration_ms = double(getTickCount() - start) * 1000 / freq;
        std::cout << "Ealpsed time for FLD " << duration_ms << " ms." << std::endl;
    }
    // Show found lines with LSD
    Mat line_image_lsd(image);
    lsd->drawSegments(line_image_lsd, lines_lsd);
    imshow("LSD result", line_image_lsd);

    // Show found lines with FLD
    Mat line_image_fld(image);
    fld->drawSegments(line_image_fld, lines_fld);
    imshow("FLD result", line_image_fld);

    waitKey();
    return 0;
}

Constructor & Destructor Documentation

virtual cv::ximgproc::FastLineDetector::~FastLineDetector ( )

inlinevirtual

Member Function Documentation

virtual void cv::ximgproc::FastLineDetector::detect ( InputArray  _image, OutputArray  _lines  )

pure virtual

Python:
	_lines	=	cv.ximgproc_FastLineDetector.detect(	_image[, _lines]	)

Finds lines in the input image. This is the output of the default parameters of the algorithm on the above shown image.

image

Parameters

_image	A grayscale (CV_8UC1) input image. If only a roi needs to be selected, use: fld_ptr-\>detect(image(roi), lines, ...); lines += Scalar(roi.x, roi.y, roi.x, roi.y);
_lines	A vector of Vec4f elements specifying the beginning and ending point of a line. Where Vec4f is (x1, y1, x2, y2), point 1 is the start, point 2 - end. Returned lines are directed so that the brighter side is on their left.

virtual void cv::ximgproc::FastLineDetector::drawSegments ( InputOutputArray  _image, InputArray  lines, bool  draw_arrow = false  )

pure virtual

Python:
	_image	=	cv.ximgproc_FastLineDetector.drawSegments(	_image, lines[, draw_arrow]	)

Draws the line segments on a given image.

Parameters

_image	The image, where the lines will be drawn. Should be bigger or equal to the image, where the lines were found.
lines	A vector of the lines that needed to be drawn.
draw_arrow	If true, arrow heads will be drawn.

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The documentation for this class was generated from the following file:

• fast_line_detector.hpp