image_alignment.cpp

/**
 * OpenCV Image Alignment  Example
 *
 * Copyright 2015 by Satya Mallick <spmallick@learnopencv.com>
 *
 */

#include "opencv2/opencv.hpp"

using namespace cv;
using namespace std;

Mat GetGradient(Mat src_gray)
{ 
	Mat grad_x, grad_y;
	Mat abs_grad_x, abs_grad_y;

	int scale = 1; 	
	int delta = 0; 
	int ddepth = CV_32FC1; ;
    
    // Calculate the x and y gradients using Sobel operator

	Sobel( src_gray, grad_x, ddepth, 1, 0, 3, scale, delta, BORDER_DEFAULT );
	convertScaleAbs( grad_x, abs_grad_x );

	Sobel( src_gray, grad_y, ddepth, 0, 1, 3, scale, delta, BORDER_DEFAULT );
	convertScaleAbs( grad_y, abs_grad_y );

    // Combine the two gradients
    Mat grad;
	addWeighted( abs_grad_x, 0.5, abs_grad_y, 0.5, 0, grad );

	return grad; 

} 


int main( int argc, char** argv )
{

	// Read 8-bit color image.
    // This is an image in which the three channels are
    // concatenated vertically.
	Mat im =  imread("images/cathedral.jpg", IMREAD_GRAYSCALE);
	
    // Find the width and height of the color image
    Size sz = im.size();
    int height = sz.height / 3;
	int width = sz.width; 
 
    // Extract the three channels from the gray scale image
	vector<Mat>channels; 
	channels.push_back(im( Rect(0, 0,         width, height)));
	channels.push_back(im( Rect(0, height,    width, height))); 
	channels.push_back(im( Rect(0, 2*height,  width, height))); 

    // Merge the three channels into one color image
	Mat im_color; 
	merge(channels,im_color);
    
    // Set space for aligned image.
    vector<Mat> aligned_channels;
    aligned_channels.push_back(Mat(height, width, CV_8UC1));
    aligned_channels.push_back(Mat(height, width, CV_8UC1));
    
    // The blue and green channels will be aligned to the red channel.
    // So copy the red channel
    aligned_channels.push_back(channels[2].clone());


    // Define motion model
	const int warp_mode = MOTION_AFFINE;
    
    // Set space for warp matrix.
	Mat warp_matrix;
    
    // Set the warp matrix to identity.
    if ( warp_mode == MOTION_HOMOGRAPHY )
		warp_matrix = Mat::eye(3, 3, CV_32F);
	else
		warp_matrix = Mat::eye(2, 3, CV_32F);

    // Set the stopping criteria for the algorithm.
    int number_of_iterations = 5000;
	double termination_eps = 1e-10;
    
    TermCriteria criteria(TermCriteria::COUNT+TermCriteria::EPS,
                          number_of_iterations, termination_eps);

    
    // Warp the blue and green channels to the red channel
	for ( int i = 0; i < 2; i++)
	{
        
		double cc = findTransformECC (
                                      GetGradient(channels[2]),
                                      GetGradient(channels[i]),
                                      warp_matrix,
                                      warp_mode,
                                      criteria
                                      );

		cout << "warp_matrix : " << warp_matrix << endl;  
		cout << "CC " << cc << endl; 
		if (cc == -1)
		{
			cerr << "The execution was interrupted. The correlation value is going to be minimized." << endl;
			cerr << "Check the warp initialization and/or the size of images." << endl << flush;
		}


		if (warp_mode == MOTION_HOMOGRAPHY)
            // Use Perspective warp when the transformation is a Homography
            warpPerspective (channels[i], aligned_channels[i], warp_matrix, aligned_channels[0].size(), INTER_LINEAR + WARP_INVERSE_MAP);
        else
            // Use Affine warp when the transformation is not a Homography
            warpAffine(channels[i], aligned_channels[i], warp_matrix, aligned_channels[0].size(), INTER_LINEAR + WARP_INVERSE_MAP);
        
	} 
	
    // Merge the three channels
    Mat im_aligned;
    merge(aligned_channels, im_aligned);

    // Show final output
	imshow("Color Image", im_color);
	imshow("Aligned Image", im_aligned);
  	waitKey(0);	

}