How to stitch an array of images into an MxN image collage

Question

So I have an array of Mat objects (jpeg images) and I want to convert that into an MxN array so the final output would be an image made of all the input images from the array, put into the matrix from left to right, then from up to down. Suppose all input images are the same size, how do I do this in C++ using Opencv?

Many thanks

Answer 1

This should do it:

#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 );
}