set color transparent in the android camera preview

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Hello everybody

My target is to make an android application with openCV, that has a camera preview. In this preview i want to filter out a color range and set it transparent.

In the background of my application, (behind the camerapreview) is a static picture that should come through the transparent part of the camera preview.

For example, I want to filter out green and set it to transparent.

http://kotao-production.com">

Question 1: is it possible to make parts of the CvCameraViewFrame transparent?

Question 2: with respect to these answers: sustract color from Mat why is following code not working?

android activity:

    public Mat onCameraFrame(CvCameraViewFrame inputFrame){
        mRgba = inputFrame.rgba();
        RemovePink(mRgba.getNativeObjAddr());       
        return mRgba;
    }
   public native void RemovePink( long matAddrRgba);

and the jni:

JNIEXPORT void JNICALL        
Java_org_opencv_samples_tutorial2_Tutorial2Activity_RemovePink(JNIEnv*, jobject, jlong addrRgba);
JNIEXPORT void JNICALL Java_org_opencv_samples_tutorial2_Tutorial2Activity_RemovePink(JNIEnv*, jobject, jlong addrRgba){

Mat& mRgba = *(Mat*)addrRgba;
Mat alpha;   
inRange(mRgba , Scalar(0,0,250),  Scalar(0,0,255),alpha);    
bitwise_not(alpha,alpha);

//split source  
Mat bgr[4];   
split(mRgba ,bgr);   

//Merge to final image including alpha   
Mat tmp[4] = { bgr[0],bgr[1],bgr[2],alpha};   
merge(mRgba ,4,dst);   
}
}

thanks in advance for every kind of help!