| OpenCV 3.4.7 Open Source Computer Vision

Public Member Functions | List of all members
cv::ximgproc::FastLineDetector Class Referenceabstract
Extended Image Processing » Fast line detector

Class implementing the FLD (Fast Line Detector) algorithm described in [114] . 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. More...
virtual void | drawSegments (InputOutputArray _image, InputArray lines, bool draw_arrow=false)=0
| Draws the line segments on a given image. More...
Public Member Functions inherited from cv::Algorithm
| Algorithm ()
virtual | ~Algorithm ()
virtual void | clear ()
| Clears the algorithm state. More...
virtual bool | empty () const
| Returns true if the Algorithm is empty (e.g. in the very beginning or after unsuccessful read. More...
virtual String | getDefaultName () const
virtual void | read (const FileNode &fn)
| Reads algorithm parameters from a file storage. More...
virtual void | save (const String &filename) const
virtual void | write (FileStorage &fs) const
| Stores algorithm parameters in a file storage. More...
void | write (const Ptr< FileStorage > &fs, const String &name=String()) const
| simplified API for language bindings This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts. More...

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

## Detailed Description

Class implementing the FLD (Fast Line Detector) algorithm described in [114] .

#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 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 the algorithm 10 times
// to see the algorithm's processing time with sufficiently warmed-up
// CPU performance.
for(int run_count = 0; run_count < 10; run_count++) {
double freq = getTickFrequency();
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 << "Elapsed time for FLD " << duration_ms << " ms." << std::endl;
}
// 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

## § ~FastLineDetector()

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

## Member Function Documentation

## § detect()

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.

Examples:
  fld_lines.cpp.

## § drawSegments()

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.

Examples:
  fld_lines.cpp.

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

- opencv2/ximgproc/fast_line_detector.hpp