Visualize image after kernel filtering

filter_webcam.cpp

#include <opencv2/opencv.hpp>
#include <opencv2/core/ocl.hpp>

int main( int argc, char ** argv )
{
  cv::VideoCapture cap;
  cv::Mat frame;

  constexpr int FILTER_SIZE = 3;
  const std::string windowName{ "Filter image" };

  std::array<float, FILTER_SIZE * FILTER_SIZE> filter_mem{{ 1.0f, 1.0f, 1.0f,
                                                            0.0f, 0.0f, 0.0f,
                                                            -1.0f, -1.0f, -1.0f }};
  const cv::Mat filter = cv::Mat( FILTER_SIZE, FILTER_SIZE, CV_32F, filter_mem.data() ) / static_cast<float>( 1 );
  cv::Point anchor = cv::Point( -1, -1 );
  cap.open( 0 );
  for( cap >> frame; !frame.empty(); cap >> frame )
  {
    cv::cvtColor( frame, frame, cv::COLOR_BGR2GRAY );
    cv::filter2D( frame, frame, -1 , filter, anchor, 0, cv::BORDER_DEFAULT );
    cv::imshow( windowName, frame );

    char key = cv::waitKey( 1 );
    if( key == 'q' || key == 27 )
      break;
  }
  cv::destroyWindow( windowName );

  return 0;
}