Cannot set user parameters in BackgroundSubtractorMOG2
background-subtraction, c++, opencv
Solution
I've just looked OpenCV source code and found interesting initialization in file `/modules/video/src/video_init.cpp`. Here it is:
CV_INIT_ALGORITHM(BackgroundSubtractorMOG2, "BackgroundSubtractor.MOG2",
obj.info()->addParam(obj, "history", obj.history);
obj.info()->addParam(obj, "nmixtures", obj.nmixtures);
obj.info()->addParam(obj, "varThreshold", obj.varThreshold);
obj.info()->addParam(obj, "detectShadows", obj.bShadowDetection));
It seems that it's possible to set only these four parameters using method `set`.
And also take a look at file `modules/video/src/bgfg_gaussmix2.cpp`, which has a `BackgroundSubtractorMOG2` class. It has the following fields:
float fVarInit;
float fVarMax;
float fVarMin;
//initial standard deviation for the newly generated components.
//It will will influence the speed of adaptation. A good guess should be made.
//A simple way is to estimate the typical standard deviation from the images.
//I used here 10 as a reasonable value
And the value `fVarMin` (which you want to change) is set to:
fVarMin = defaultVarMin2
in both constructors. Here are all of them:
static const float defaultVarInit2 = 15.0f; // initial variance for new components
static const float defaultVarMax2 = 5*defaultVarInit2;
static const float defaultVarMin2 = 4.0f;
And interesting fact that this value is not used in any other file, so it seems that it's impossible to change it for now. You can post this issue directly to OpenCV bugtracker.
Problem
OpenCV library version 2.42. I'd like to set a parameter in `BackgroundSubtractorMOG2` object, e.g. ``` BackgroundSubtractorMOG2 bgr; // the following doesn't work because 'nmixtures', 'backgroundRatio' // and 'fVarMin' are a protected members. bgr.nmixtures = 3; bgr.backgroundRatio = 0.9; bgr.fVarMin = 5; // the following works bgr.set('nmixtures', 3); // both of the following lines will give a run-time error // `Access violation reading location 0x0000000000000008.` bgr.set("backgroundRatio", 0.9); bgr.set("fVarMin", 5); ``` `backgroundRatio` and `fVarMin` are parameters that control the algorithm. User should be able to change these parameters according to the documentation. How can I set the parameters of `BackgroundSubtractorMOG2`? EDIT As correctly mentioned in the answer below, this was a bug in OpenCV. The bug was fixed in OpenCV version 2.4.6.