Adding pixel data from two ofxCvFloatImage instances

I am trying to combine two ofxCvFloatImage instances from some optical flow with the ofxOpenCv built in addon.

I have the split the flow into separate images flowX describing the motion of each pixel in the x-axis and flowY describing the motion in the y-axis.

From the documentation in ofxCvColorImage this shows you can add pixel data from one to another:

first += second; // both are ofxCvFloatImage instances

However, I am unable to do this and get and error: “Invalid operands to binary expression (‘ofxCvFloatImage’ and ‘ofxCvFloatImage’)”

Any help on adding pixel data from two ofxCvFloatImage instances would be great.
Here is the code I’m working with.

        Mat img1( gray1.getCvImage() );  //Create OpenCV images
        Mat img2( gray2.getCvImage() );
        Mat flow;                        //Image for flow
        calcOpticalFlowFarneback( img1, img2, flow, 0.7, 3, 11, 5, 5, 1.1, 0 );

        //Split flow into separate images
        //describing the motion of each pixel in the x-axis and one describing the motion in the y-axis

        vector<Mat> flowPlanes;

        split( flow, flowPlanes );
        //Copy float planes to ofxCvFloatImage images flowX and flowY
        IplImage iplX( flowPlanes[0] );
        flowX = &iplX;
        IplImage iplY( flowPlanes[1] );
        flowY = &iplY;

        //Need to combine flowX and flowY which are of type ofxCvFloatImage
        //Or convert the flow into one CVimage.

This seems to work like this. Must have been a silly mistake.

        flowX += flowY;
        flowXY = flowX;
        flXY = flowXY.getFloatPixelsRef();

However, now I see that movement only seems to work in one direction in the X and Y axis. A separate issue though.