Count 'white' pixels in opencv binary image (efficiently)

Question

I am trying to count all the white pixels in an OpenCV binary image. My current code is as follows:

  whitePixels = 0;
  for (int i = 0; i < height; ++i)
    for (int j = 0; j < width; ++j)
      if (binary.at<int>(i, j) != 0)
        ++whitePixels;

However, after profiling with gprof I've found that this is a very slow piece of code, and a large bottleneck in the program.

Is there a method which can compute the same value faster?

Answer 1

cv::CountNonZero. Usually the OpenCV implementation of a task is heavily optimized.