OpenCV  4.10.0
Open Source Computer Vision
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Structured forests for fast edge detection

Introduction

In this tutorial you will learn how to use structured forests for the purpose of edge detection in an image.

Examples

image
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Note
binarization techniques like Canny edge detector are applicable to edges produced by both algorithms (Sobel and StructuredEdgeDetection::detectEdges).

Source Code

1/**************************************************************************************
2The structured forests for fast edge detection demo requires you to provide a model.
3This model can be found at the opencv_extra repository on Github on the following link:
4https://github.com/opencv/opencv_extra/blob/master/testdata/cv/ximgproc/model.yml.gz
5***************************************************************************************/
6
7#include <opencv2/ximgproc.hpp>
8#include "opencv2/highgui.hpp"
9#include <iostream>
10
11using namespace cv;
12using namespace cv::ximgproc;
13
14const char* keys =
15{
16 "{i || input image file name}"
17 "{m || model file name}"
18 "{o || output image file name}"
19};
20
21int main( int argc, const char** argv )
22{
23 CommandLineParser parser(argc, argv, keys);
24 parser.about("This sample demonstrates usage of structured forests for fast edge detection");
25 parser.printMessage();
26
27 if ( !parser.check() )
28 {
29 parser.printErrors();
30 return -1;
31 }
32
33 String modelFilename = parser.get<String>("m");
34 String inFilename = parser.get<String>("i");
35 String outFilename = parser.get<String>("o");
36
38 Mat image = imread(inFilename, IMREAD_COLOR);
39 if ( image.empty() )
40 CV_Error(Error::StsError, String("Cannot read image file: ") + inFilename);
42
43 if ( modelFilename.size() == 0)
44 CV_Error(Error::StsError, String("Empty model name"));
45
47 image.convertTo(image, DataType<float>::type, 1/255.0);
49
50 TickMeter tm;
51 tm.start();
53 Ptr<StructuredEdgeDetection> pDollar =
54 createStructuredEdgeDetection(modelFilename);
56
57 tm.stop();
58 std::cout << "createStructuredEdgeDetection() time : " << tm << std::endl;
59
60 tm.reset();
61 tm.start();
63 Mat edges;
64 pDollar->detectEdges(image, edges);
66 tm.stop();
67 std::cout << "detectEdges() time : " << tm << std::endl;
68
69 tm.reset();
70 tm.start();
72 // computes orientation from edge map
73 Mat orientation_map;
74 pDollar->computeOrientation(edges, orientation_map);
75
76 // suppress edges
77 Mat edge_nms;
78 pDollar->edgesNms(edges, orientation_map, edge_nms, 2, 0, 1, true);
80
81 tm.stop();
82 std::cout << "nms time : " << tm << std::endl;
83
85 if ( outFilename.size() == 0 )
86 {
87 imshow("edges", edges);
88 imshow("edges nms", edge_nms);
89 waitKey(0);
90 }
91 else
92 imwrite(outFilename, 255*edges);
94
95 return 0;
96}
cv::CommandLineParser
Designed for command line parsing.
Definition utility.hpp:820
cv::DataType
Template "trait" class for OpenCV primitive data types.
Definition traits.hpp:113
cv::Mat
n-dimensional dense array class
Definition mat.hpp:812
cv::TickMeter
a Class to measure passing time.
Definition utility.hpp:295
cv::TickMeter::start
void start()
starts counting ticks.
Definition utility.hpp:304
cv::TickMeter::stop
void stop()
stops counting ticks.
Definition utility.hpp:310
cv::TickMeter::reset
void reset()
resets internal values.
Definition utility.hpp:374
cv::String
std::string String
Definition cvstd.hpp:151
cv::Ptr
std::shared_ptr< _Tp > Ptr
Definition cvstd_wrapper.hpp:23
CV_Error
#define CV_Error(code, msg)
Call the error handler.
Definition base.hpp:320
cv::imshow
void imshow(const String &winname, InputArray mat)
Displays an image in the specified window.
cv::waitKey
int waitKey(int delay=0)
Waits for a pressed key.
cv::IMREAD_COLOR
@ IMREAD_COLOR
If set, always convert image to the 3 channel BGR color image.
Definition imgcodecs.hpp:71
cv::imwrite
CV_EXPORTS_W bool imwrite(const String &filename, InputArray img, const std::vector< int > &params=std::vector< int >())
Saves an image to a specified file.
cv::imread
CV_EXPORTS_W Mat imread(const String &filename, int flags=IMREAD_COLOR)
Loads an image from a file.
cv::ximgproc::createStructuredEdgeDetection
Ptr< StructuredEdgeDetection > createStructuredEdgeDetection(const String &model, Ptr< const RFFeatureGetter > howToGetFeatures=Ptr< RFFeatureGetter >())
main
int main(int argc, char *argv[])
Definition highgui_qt.cpp:3
cv::Error::StsError
@ StsError
unknown /unspecified error
Definition base.hpp:71
cv::ximgproc
Definition ximgproc.hpp:125
cv
"black box" representation of the file storage associated with a file on disk.
Definition core.hpp:102

Explanation

  1. Load source color image

    Mat image = imread(inFilename, IMREAD_COLOR);
    if ( image.empty() )
    CV_Error(Error::StsError, String("Cannot read image file: ") + inFilename);

  2. Convert source image to float [0;1] range

    image.convertTo(image, DataType<float>::type, 1/255.0);

  3. Run main algorithm

    Ptr<StructuredEdgeDetection> pDollar =
    createStructuredEdgeDetection(modelFilename);
    Mat edges;
    pDollar->detectEdges(image, edges);
    // computes orientation from edge map
    Mat orientation_map;
    pDollar->computeOrientation(edges, orientation_map);
    // suppress edges
    Mat edge_nms;
    pDollar->edgesNms(edges, orientation_map, edge_nms, 2, 0, 1, true);

  4. Show results

    if ( outFilename.size() == 0 )
    {
    imshow("edges", edges);
    imshow("edges nms", edge_nms);
    waitKey(0);
    }
    else
    imwrite(outFilename, 255*edges);

Literature

For more information, refer to the following papers : [Dollar2013] [Lim2013]

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