Stitch images into a MxN collage

image_collage.cpp

#include <opencv2/opencv.hpp>

cv::Mat imageCollage( std::vector<cv::Mat> & array_of_images, int M, int N )
{
  // All images should be the same size
  const cv::Size images_size = array_of_images[0].size();
  // Create a black canvas
  cv::Mat image_collage( images_size.height * N, images_size.width * M, CV_8UC3, cv::Scalar( 0, 0, 0 ) );

  for( int i = 0; i < N; ++i )
  {
    for( int j = 0; j < M; ++j )
    {
      if( ( ( i * M ) + j ) >= array_of_images.size() )
        break;

      cv::Rect roi( images_size.width * j, images_size.height * i, images_size.width, images_size.height );
      array_of_images[ ( i * M ) + j ].copyTo( image_collage( roi ) );
    }
  }
  
  return image_collage;
}


int main()
{
  std::vector<cv::Mat> array_of_images;
  array_of_images.push_back( cv::imread( "1.jpg" ) );
  array_of_images.push_back( cv::imread( "2.jpg" ) );
  cv::Mat image_collage = imageCollage( array_of_images, 3, 3 );

  cv::imshow( "Image Collage", image_collage );
  cv::waitKey( 0 );
}