How to disable shadow detection in MoG2

Question

I am using C++ and Opencv 2.3.1 for background subtraction. I have tried many times to change the parameters of Mog2 in order to disable shadow detection feature also i have tried what other people suggest on the internet. however, the shadow detection still enabled.

could you please tell me how to disable it? see the sample code and the generated mask.

  //opencv
#include < opencv2/opencv.hpp>
#include < opencv2/core/core.hpp>
#include < opencv2/highgui/highgui.hpp>
#include < opencv2/video/background_segm.hpp>
#include < opencv2/imgproc/imgproc.hpp>
#include < opencv2/video/video.hpp>

//C
 #include <stdio.h>
 //C++
#include <iostream>
#include <sstream>

using namespace cv;
using namespace std;

// Global variables
Mat frame; //current frame
Mat fgMaskMOG2; //fg mask fg mask generated by MOG method
Ptr<BackgroundSubtractor> pMOG2; //MOG Background subtractor
int keyboard; //input from keyboard

//new variables
int history = 1250;
float varThreshold = 16;
bool bShadowDetection = true;

/*
//added to remove the shadow
unsigned char nShadowDetection = 0;
float fTau = 0.5;
//static const unsigned char nShadowDetection =( unsigned char)0;
 */
    // Function Headers 
   void help();
   void processImages(char* firstFrameFilename);

 void help()
{
cout
   << "This program shows how to use background subtraction methods provided   by "  << endl
  << " OpenCV. You can process  images (-img)."                                     << endl                                                                      
    << "Usage:"                                                                     << endl
   << "./bs -img <image filename>}"                                                << endl
   << "for example: ./bs -img /data/images/1.png"                                  << endl
   << endl;
  }

// morphological operation

void morphOps(Mat &thresh){

   //create structuring element that will be used to "dilate" and "erode"   image.
   //the element chosen here is a 3px by 3px rectangle

   Mat erodeElement = getStructuringElement( MORPH_RECT,Size(2,2)); //3x3
   //dilate with larger element so make sure object is nicely visible
   Mat dilateElement = getStructuringElement( MORPH_RECT,Size(1,1)); //8x8

  erode(thresh,thresh,erodeElement);
  erode(thresh,thresh,erodeElement);


    dilate(thresh,thresh,dilateElement);
    dilate(thresh,thresh,dilateElement);

}


// main function

int main(int argc, char* argv[])
{

 //print help information
 help();

 //check for the input parameter correctness
 if(argc != 3) {
    cerr <<"Incorret input list" << endl;
    cerr <<"exiting..." << endl;
    return EXIT_FAILURE;
 }

  //create GUI windows
  namedWindow("Frame");
  namedWindow("FG Mask MOG2 ");

 //create Background Subtractor objects
 //pMOG2 = new BackgroundSubtractorMOG2();
  pMOG2 = new BackgroundSubtractorMOG2( history,   varThreshold,     bShadowDetection);
//BackgroundSubtractorMOG2(int history,  float varThreshold, bool   bShadowDetection=1);
    if(strcmp(argv[1], "-img") == 0) {
    //input data coming from a sequence of images
    processImages(argv[2]);
 }
 else {
    //error in reading input parameters
    cerr <<"Please, check the input parameters." << endl;
    cerr <<"Exiting..." << endl;
    return EXIT_FAILURE;
 }
 //destroy GUI windows
 destroyAllWindows();
 return EXIT_SUCCESS;
}

 //function processImages

 void processImages(char* fistFrameFilename) {
  //read the first file of the sequence
  frame = imread(fistFrameFilename);
  if(frame.empty()){
     //error in opening the first image
     cerr << "Unable to open first image frame: " << fistFrameFilename <<   endl;
     exit(EXIT_FAILURE);

 //current image filename
 string fn(fistFrameFilename);
 //read input data. ESC or 'q' for quitting
  while( (char)keyboard != 'q' && (char)keyboard != 27 ){
     //update the background model
     pMOG2->operator()(frame, fgMaskMOG2,-1);
     //get the frame number and write it on the current frame
     size_t index = fn.find_last_of("/");
     if(index == string::npos) {
        index = fn.find_last_of("\\");
     }
    size_t index2 = fn.find_last_of(".");
    string prefix = fn.substr(0,index+1);
    string suffix = fn.substr(index2);
    string frameNumberString = fn.substr(index+1, index2-index-1);
    istringstream iss(frameNumberString);
    int frameNumber = 0;
    iss >> frameNumber;
    rectangle(frame, cv::Point(10, 2), cv::Point(100,20),
              cv::Scalar(255,255,255), -1);
    putText(frame, frameNumberString.c_str(), cv::Point(15, 15),
            FONT_HERSHEY_SIMPLEX, 0.5 , cv::Scalar(0,0,0));
    //show the current frame and the fg masks
    imshow("Frame", frame);
    morphOps(fgMaskMOG2);
    imshow("FG Mask MOG2 ", fgMaskMOG2);
    //get the input from the keyboard
    keyboard = waitKey(1);
    //search for the next image in the sequence
    ostringstream oss;
    oss << (frameNumber + 1);
    string nextFrameNumberString = oss.str();
    string nextFrameFilename = prefix + nextFrameNumberString + suffix;
    //read the next frame
    frame = imread(nextFrameFilename);
    if(frame.empty()){
        //error in opening the next image in the sequence
        cerr << "Unable to open image frame: " << nextFrameFilename << endl;
        exit(EXIT_FAILURE);
    }
    //update the path of the current frame
    fn.assign(nextFrameFilename);

    // save subtracted images
    string imageToSave =("output_MOG_" +  frameNumberString + ".png");
    bool saved = imwrite(  "D:\\SO\\temp\\" +imageToSave,fgMaskMOG2);
    if(!saved) {
    cerr << "Unable to save " << imageToSave << endl;
       }
}
}

}

Answer 1

it depends on what you really want to see - if you want to separate the shadows from your segmentation:

bool bShadowDetection = true; and use cv::threshold(Mask,Mask,254,255,cv::THRESH_BINARY); after MOG2->apply()

you'll get exactly the part of wich is {255} in your image

and sry for reanimating this...

Answer 2

take a look at the documentation

on your code you have

bool bShadowDetection = true;

change it to

bool bShadowDetection = false;

EDIT: OpenCV 3's BackgroundSubtractorMOG2 Class has setShadowValue (int value) function to set gray value of shadow. setting value of gray to zero will remove the shadow.