CMake a project with OpenCV in Mac OS X - 'opencv2/opencv.hpp' file not found

I wrote a simple opencv project containing only a main.cpp file:

// main.cpp
#include <opencv/cv.h>
#include <opencv2/opencv.hpp>
int main()
{
    cv::Mat I = cv::imread("img.png");
    cv::imshow("img",I);
    cv::waitKey(0);
    return 0;
}

Then to build it, I wrote a CMakeLists.txt like this, which is actually copied from http://docs.opencv.org/doc/tutorials/introduction/linux_gcc_cmake/linux_gcc_cmake.html

cmake_minimum_required(VERSION 2.8)
project( DisplayImage )
find_package( OpenCV REQUIRED )
add_executable( DisplayImage main.cpp )
target_link_libraries( DisplayImage ${OpenCV_LIBS} )

In terminal, first I ran cmake . and a Makefile was generated. Then I ran make and got the following error:

fatal error: 
  'opencv2/opencv.hpp' file not found
#include <opencv2/opencv.hpp>
         ^
......

It seems the compiler cannot find OpenCV include dir. But I don't know where to add it to the CMakeLists.txt. My platform is Mac OS X 10.10, and OpenCV include and lib files have been installed at /usr/local/include and /usr/local/lib already. However, in Ubuntu, the compiler can find it and successfully build the project.

So what is a correct CMakeLists.txt in Mac OS X?