When I try to sum up N previous frames stored in a list and then dividing by num frames, the background model produced is not as expected. I can tell because I've tried the algo in Matlab earlier on the same video.
class TemporalMeanFilter {
private:
int learningCount;
list<Mat> history;
int height, width;
Mat buildModel(){
if(history.size() == 0)
return Mat();
Mat image_avg(height, width, CV_8U, Scalar(0));
double alpha = (1.0/history.size());
list<Mat>::iterator it = history.begin();
cout << "History size: " << history.size() << " Weight per cell: " << alpha << endl;
while(it != history.end()){
image_avg += (*it * alpha);
it++;
}
return image_avg;
}
public:
TemporalMeanFilter(int height, int width, int learningCount){
this->learningCount = learningCount;
this->height = height;
this->width = width;
}
void applyFrameDifference(Mat& frame_diff, Mat& bg_model, Mat& input_frame){
if(history.size() == learningCount)
history.pop_front();
history.push_back(input_frame);
bg_model = buildModel();
frame_diff = bg_model - input_frame;
}
};
//The main looks like this
// ... reading video from file
TemporalMeanFilter meanFilter(height, width, 50); //background subtraction algorithm
meanFilter.applyFrameDifference(diff_frame, bg_model, curr_frame);
//... displaying on screen ... prog ends
Image:
http://imagegur.com/images/untitled.png
The left one is the bg_model, the middle is the curr_frame, and the right one is the output.
Maybe it's because of the rounding off done on CV_U8? I tried changing to CV_32FC1, but then the program just crashed because for some reason it couldn't add two CV_32FC1 Matrices.
Any insight would be greatly appreciated. Thanks!
More Info:
Inside the class, I now keep the average in a CV_16UC1 Mat to prevent clipping, how it results in an error after successive addition.
The add function / operator + both change the type of result from CV_16UC1 to CV8UC1. This error is caused by that. Any suggestion how to ask it preserve the original datatype? (PS: I asked politely... didn't work)
background_model += *it;
OpenCV Error: Bad argument (When the input arrays in add/subtract/multiply/divid
e functions have different types, the output array type must be explicitly speci
fied) in unknown function, file C:\buildslave64\win64_amdocl\2_4_PackSlave-win32
-vc11-shared\opencv\modules\core\src\arithm.cpp, line 1313