Question

I’am actually working in a project on android in which I want to extract some specific pixel values (according to a condition, using the threshold method , I have set some pixels to a certain values and all the others to zero) I want to extract all these values different from zero in a vector. I will use this vector of the chosen pixels to do some operation ( the mean value for exemple ) , Is there a method in OpenCV that can help me doing this ?

Thank you 🙂

Answer 1

I don’t know such function but actually it’s not hard to implement it (c++):

//'in' should be CV_8UC3
vector<int>& getNonZero(const Mat& in)
{
    //get size of result vector
    //this is all non-zero pixels:
    int count = countNonZero(in);
    vector<int>& result(count);
    int k = 0;

    for (int r = 0; r < in.rows; ++r)
    {
        for (int c = 0; c < in.cols; ++c)
        {
          if (in.at<int>(r, c))
          {
              result[k++] = in.at<int>(r, c);
          }
        }
    }

    return result;
}

And also many OpenCV functions have InputArray mask parameter so use it! For example:

void meanStdDev(InputArray src, OutputArray mean, OutputArray stddev, InputArray mask=noArray())