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copied!<p>fix</p> <ul> <li>change <code>_fgmask.create(img_input.size(), CV_8U);</code> to <code>_fgmask.create(img_input.size(), CV_8UC3);</code> or <code>_fgmask.create(img_input.size(), img_input.type());</code> </li> </ul> <p>why</p> <ul> <li>this is because <code>cv::absdiff(img_input_prev, img_input, img_foreground);</code> recreate a new array everytime internally. and it does update the img_foreground structure but after the allocation, the memory address data inside _fgmask fail to change since the headers are passed by value. <ul> <li>you can seemlingly fix this(but still incurs creation cost) by doing <code>cv::Mat& img_foreground = _fgmask.getMatRef();</code></li> </ul></li> <li>and that is because CV_8U is not the same as CV_8UC3 and therefore the check @ Mat::create() in mat.hpp always end up allocating a new array due to type difference</li> </ul> <p>opinion</p> <p>i think...maybe use Mat instead?</p> <pre><code>#include "opencv2/opencv.hpp" using namespace cv; class FrameDifferenceBGS { public: Mat prev; Mat diff; bool enableThreshold; bool showOutput; bool firstTime; uchar threshold; FrameDifferenceBGS():firstTime(false),enableThreshold(false),showOutput(false),threshold(0) { } void FrameDifferenceBGS::operator()(cv::Mat& _in, cv::Mat &_fg, double _lr) { if(_in.empty()) return; if(prev.empty()) { prev=_in.clone(); _fg=cv::Mat::zeros(_in.size(),CV_8UC1); return; } cv::absdiff(prev, _in, diff); if(diff.channels() == 3) cv::cvtColor(diff, _fg, CV_BGR2GRAY); else _fg=diff; if(enableThreshold) cv::threshold(_fg, _fg, threshold, 255, cv::THRESH_BINARY); if(showOutput) cv::imshow("Frame Difference", _fg); prev=_in.clone(); firstTime = false; } }; int main() { VideoCapture cap(0); FrameDifferenceBGS bgs; Mat frame,fg; for(;;) { cap >> frame; bgs(frame,fg,0); imshow("frame", frame); imshow("fg", fg); if(waitKey(1) ==27) exit(0); } return 0; } </code></pre> <h2>edit 2(modified original)</h2> <pre><code>#include "opencv2/opencv.hpp" class FrameDifferenceBGS { public: cv::Mat img_input_prev; cv::Mat diff; cv::Mat img_foreground;//put this in class in stead of inside the function bool enableThreshold; bool showOutput; bool firstTime; uchar threshold; FrameDifferenceBGS():firstTime(false),enableThreshold(false),showOutput(false),threshold(0) { } void FrameDifferenceBGS::operator()(cv::InputArray _image, cv::OutputArray _fgmask, double learningRate) { cv::Mat img_input = _image.getMat(); if(img_input.empty()) return; if(_fgmask.empty()) _fgmask.create(img_input.size(), CV_8UC1); if(img_input_prev.empty()) { img_input.copyTo(img_input_prev); return; } cv::absdiff(img_input_prev, img_input, img_foreground); if(img_foreground.channels() == 3) cv::cvtColor(img_foreground, _fgmask, CV_BGR2GRAY); if(enableThreshold) cv::threshold(img_foreground, img_foreground, threshold, 255, cv::THRESH_BINARY); if(showOutput) cv::imshow("Frame Difference", img_foreground); img_input.copyTo(img_input_prev); //img_foreground.copyTo(_fgmask); firstTime = false; } }; int main() { cv::VideoCapture cap(0); FrameDifferenceBGS bgs; cv::Mat frame,fg; for(;;) { cap >> frame; bgs(frame,fg,0); cv::imshow("frame", frame); cv::imshow("fg", fg); if(cv::waitKey(1) ==27) exit(0); } return 0; } </code></pre>

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