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I'm using the MOG2 algorithm for background subtration in opencv 3.2. I want to look at the learned gaussian mixture models(weights, variance, mean...), however opencv does not provide built-in function to look at the values.

In bgfg_gaussmix2.cpp source code, I found the variables I need in class BackgroundSubtractorMOG2Impl:

UMat u_weight;
UMat u_variance;
UMat u_mean;
UMat u_bgmodelUsedMod

So what I did is just put some functions that can return the variables(in the same format as the built-in functions)

 virtual UMat getWeight() const { return u_weight; }
 virtual UMat getVariance() const { return u_variance; }
 virtual UMat getMean() const { return u_mean; }
 virtual UMat getNmodes() const {return u_bgmodelUsedModes;}

Then I also added the following to the background_segm.hpp file, in class CV_EXPORTS_W BackgroundSubtractorMOG2:

CV_WRAP virtual UMat getWeight() const = 0;
CV_WRAP virtual UMat getVariance() const = 0;
CV_WRAP virtual UMat getMean() const = 0;
CV_WRAP virtual UMat getNmodes() const = 0;

After this, I build and install the modified opencv source code. Then I wrote my own program to run the backgroundubtractorMOG2 algorithm. I can call the new functions I added to the opencv source code, but the returned UMats are just full of zeros.

So my question is how to get the UMats in the right way?

James Brown
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  • You only will be able to access the UMat values for the cases where you are running MOG2 with the OpenCL implementation. http://stackoverflow.com/questions/33602675/what-is-the-difference-between-umat-and-mat-in-opencv Is this your case? – Eliezer Bernart Mar 25 '17 at 05:32

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