blend one image with another using an alpha mask in c++ w/opencv

alpha_mask_blend.cc

void alphaBlend(Mat& foreground, Mat& background, Mat& alpha, Mat& outImage)
{
     // Find number of pixels. 
     int numberOfPixels = foreground.rows * foreground.cols * foreground.channels();
 
     // Get floating point pointers to the data matrices
     float* fptr = reinterpret_cast<float*>(foreground.data);
     float* bptr = reinterpret_cast<float*>(background.data);
     float* aptr = reinterpret_cast<float*>(alpha.data);
     float* outImagePtr = reinterpret_cast<float*>(outImage.data);
 
     // Loop over all pixesl ONCE
     for( 
       int i = 0; 
       i < numberOfPixels; 
       i++, outImagePtr++, fptr++, aptr++, bptr++
     )
     {
         *outImagePtr = (*fptr)*(*aptr) + (*bptr)*(1 - *aptr);
     }
}