Error Message “Xcode alone is not sufficient on Sierra”

Question

I\'d like to install openCV to vectorize image, but there\'s a series error message regarding Xcode and Ruby.

First, I use terminal to install openCV, brew install

Answer 1

I got the same message despite having Xcode and the command line tools already being installed a long time ago and updated numerous times.

I think it is the Apple way of telling you that Xcode command line tools need to be updated, as the App Store showed me the below:

After executing the xcode-select --install command, the update disappears from the App Store, which means they are exactly the same thing.