How to assigne a cv::Scalar to cv::Mat?

Question

Using the class Scalar implemented in OpenCV, I didn't understand what is the difference between this code:

Mat test;
test = Scalar::all(0);

and this:

Mat test = Scalar::all(0);
         ^

My question is why is the first assignment correct while the second is not?

Do they both compile? I prefer the first, but I think the second would compile. — Pam, Feb 22 '18 at 20:46
The first compile, the second don't. And rafix07 answered this. — BrainabilGH, Feb 22 '18 at 21:19

score 2 · Accepted Answer · answered Feb 22 '18 at 20:48

Declaration of Mat constructor which takes Vec<_Tp,n> as parameter is

  template<typename _Tp, int n>
  explicit Mat(const Vec<_Tp, n>& vec, bool copyData=true);

cv::Scalar is treated as Vec<_Tp,4> so you can pass Scalar to Mat constructor in explicit way Class obj(parameter); not Class obj = parameter; so call

Mat test(Scalar::all(0));

How to assigne a cv::Scalar to cv::Mat?

1 Answers1