Split image into an MxN grid

split_image.cpp

#include <opencv2/opencv.hpp>

std::vector<cv::Mat> splitImage( cv::Mat & image, int M, int N )
{
  // All images should be the same size ...
  int width  = image.cols / M;
  int height = image.rows / N;
  // ... except for the Mth column and the Nth row
  int width_last_column = width  + ( image.cols % width  );
  int height_last_row   = height + ( image.rows % height );

  std::vector<cv::Mat> result;

  for( int i = 0; i < N; ++i )
  {
    for( int j = 0; j < M; ++j )
    {
      // Compute the region to crop from
      cv::Rect roi( width  * j,
                    height * i,
                    ( j == ( M - 1 ) ) ? width_last_column : width,
                    ( i == ( N - 1 ) ) ? height_last_row   : height );

      result.push_back( image( roi ) );
    }
  }

  return result;
}


int main()
{
  cv::Mat image = cv::imread( "image.png" );
  std::vector<cv::Mat> array_of_images = splitImage( image, 3, 2 );

  for( int i = 0; i < array_of_images.size(); ++i )
  {
    cv::imshow( "Image " + std::to_string( i ), array_of_images[i] );
  }
  cv::waitKey( 0 );
}