This example was based on the addweighted.cpp algorithm and answers to the proposed exercises at agostinhobritojr.github.io.

This program adds three more functions to the provided example. Through these functions, the tiltyshift.cpp program makes the following adjustments:

1. Adjust the height of the focus centre of the image
2. Adjust the decay of the blurred area
3. Adjust the vertical position of the focus centre area of the filtered image

#include <iostream>
#include <opencv2/opencv.hpp>
#include <cmath>

using namespace cv;
using namespace std;

double alfa;


int center_slider=0;
int center_slider_max=100;

int alfa_slider = 0;
int alfa_slider_max = 100;
// height
int top_slider = 0;
int top_slider_max = 100;
Mat image1, image2, blended;
Mat imageTop;

char TrackbarName[50];

void on_trackbar_blend(int, void*){
 alfa = (double) alfa_slider/alfa_slider_max ;
 addWeighted( image2, alfa, imageTop, 1-alfa, 0.0, blended);
 imshow("addweighted", blended);
}

void on_trackbar_line(int, void*){
  image2.copyTo(imageTop);

  int width = image2.size().width;
  int height = image2.size().height;
  int limit = top_slider*height/100;
  int base = center_slider*height/100;


  if(limit > 0){


    if(base >= 0 && base <= height-limit){
      Mat tmp = image1(Rect(0, base, width,limit));
      tmp.copyTo(imageTop(Rect(0, base, width,limit)));
    }

    else{
      Mat tmp = image1(Rect(0, 0, width,limit));
      tmp.copyTo(imageTop(Rect(0, 0, width,limit)));
    }
  }

  on_trackbar_blend(alfa_slider,0);
}

int main(int argvc, char** argv){
  image1 = imread("img/sydney7.jpg");
  resize(image1,image1,Size(640,480));
  image1.copyTo(image2);
  namedWindow("addweighted", 1);
  image2.convertTo(image2,CV_32F);

  
  float media[]={1,1,1,
               1,1,1,
               1,1,1};
  Mat mascara;
  mascara = Mat(3,3,CV_32F,media);
  scaleAdd(mascara, 1/9.0, Mat::zeros(3,3,CV_32F), mascara);

  for (int i = 0; i < 7; i++) {
        filter2D(image2, image2, image2.depth(), mascara, Point(1,1), 0);
  }
  image2.convertTo(image2, CV_8U);
  image2.copyTo(imageTop);
  sprintf( TrackbarName, "Decay x %d", alfa_slider_max );
  createTrackbar( TrackbarName, "addweighted",
          &alfa_slider,
          alfa_slider_max,
          on_trackbar_blend );
  on_trackbar_blend(alfa_slider, 0 );

  sprintf( TrackbarName, "Hight x %d", top_slider_max );
  createTrackbar( TrackbarName, "addweighted",
          &top_slider,
          top_slider_max,
          on_trackbar_line );
  on_trackbar_line(top_slider, 0 );

  sprintf( TrackbarName, "Center x %d", top_slider_max );
  createTrackbar( TrackbarName, "addweighted",
          &center_slider,
          center_slider_max,
          on_trackbar_line );
  on_trackbar_line(center_slider, 0 );

  waitKey(0);
  imwrite("tiltyshift.jpg", blended);
  imshow("window",blended);
  imwrite("original.jpg", image1);
  imshow("window2",image1);
  return 0;
}

Original image

Filtered image