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QuadrangleInPicture

Quick introduction

Shows how to embed a quadrangle video into a picture using OpenCV C++.

This is the output. enter image description here

Description

You have an image and want to embed on top of the image another image. **Note that when I say image, it can also be video as video is a series of images. If the image you want to embed is a square or rectangle, there are other simpler methods. This method is overkill for square or rectangle. But if the image you want to embed is a quadrangle(four sided polygon) but not square or rectangle, this method suits you. We will use homography matrix and warped perspective.

Your inputs:

  1. background image enter image description here
  2. video to be embed Freely available The Incredibles 2 trailer
  3. The coordinate of the embedded target.

Steps

  1. Setup the background image and video.

     // setup background image
 String backgroundFilename("background.jpg"); 
 Mat background = imread(backgroundFilename, CV_LOAD_IMAGE_COLOR);

 // setup video capture
 VideoCapture cap("incredibles-2-trailer-1_h480p.mov");
 if (!cap.isOpened())
 {
 	cout << "Error opening";
 	return -1;
 }

 // the video we want to put in background
 Mat video;
 cap >> video;

  2. Define the video region (we use whole video resolution) and its corresponding region in the background image.

     // video source
 vector<Point> left_image;      
 left_image.push_back(Point(0, 0));
 left_image.push_back(Point(0, video.rows));
 left_image.push_back(Point(video.cols, video.rows));
 left_image.push_back(Point(video.cols, 0));

 // corresponding video coordinate destination
 vector<Point> right_image;
 right_image.push_back(Point(100, 100));
 right_image.push_back(Point(200, 500));
 right_image.push_back(Point(900, 650));
 right_image.push_back(Point(700, 200));

  3. Calculate homography matrix.

     // once we get 4 corresponding points in both images calculate homography matrix
 Mat H = findHomography(left_image, right_image, 0);

  4. Warped perspective.

     // warped perspective
 Mat warpedImage;
 warpPerspective(video, warpedImage, H, background.size());

enter image description here

  1. Paint the region in the background image where we want to paste the video to black.

     // create a mask at background
 int num = 4;
 const Point *pt4 = &(right_image[0]);
 fillPoly(background, &pt4, &num, 1, Scalar(0, 0, 0), 8);

enter image description here 6. Sum background image with warped perspective image. (Any colored pixel summed with black pixel will results to the colored pixel).

enter image description here

Compile notes

The project is setup based on OpenCV official tutorial (property sheets setup). Check Visual Studio property manager and assign your configured property sheets.