/*M///////////////////////////////////////////////////////////////////////////////////////
//
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//  By downloading, copying, installing or using the software you agree to this license.
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// Copyright (C) 2013, Alfonso Sanchez-Beato, all rights reserved.
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#include "precomp.hpp"
#include "opencv2/reg/mappergradeuclid.hpp"
#include "opencv2/reg/mapaffine.hpp"

namespace cv {
namespace reg {


////////////////////////////////////////////////////////////////////////////////////////////////////
MapperGradEuclid::MapperGradEuclid(void)
{
}


////////////////////////////////////////////////////////////////////////////////////////////////////
MapperGradEuclid::~MapperGradEuclid(void)
{
}


////////////////////////////////////////////////////////////////////////////////////////////////////
void MapperGradEuclid::calculate(
    const cv::Mat& img1, const cv::Mat& image2, cv::Ptr<Map>& res) const
{
    Mat gradx, grady, imgDiff;
    Mat img2;

    CV_DbgAssert(img1.size() == image2.size());
    CV_DbgAssert(img1.channels() == image2.channels());
    CV_DbgAssert(img1.channels() == 1 || img1.channels() == 3);

    if(!res.empty()) {
        // We have initial values for the registration: we move img2 to that initial reference
        res->inverseWarp(image2, img2);
    } else {
        img2 = image2;
    }

    // Matrices with reference frame coordinates
    Mat grid_r, grid_c;
    grid(img1, grid_r, grid_c);

    // Get gradient in all channels
    gradient(img1, img2, gradx, grady, imgDiff);

    // Calculate parameters using least squares
    Matx<double, 3, 3> A;
    Vec<double, 3> b;
    // For each value in A, all the matrix elements are added and then the channels are also added,
    // so we have two calls to "sum". The result can be found in the first element of the final
    // Scalar object.
    Mat xIy_yIx = grid_c.mul(grady);
    xIy_yIx -= grid_r.mul(gradx);

    A(0, 0) = sum(sum(gradx.mul(gradx)))[0];
    A(0, 1) = sum(sum(gradx.mul(grady)))[0];
    A(0, 2) = sum(sum(gradx.mul(xIy_yIx)))[0];
    A(1, 1) = sum(sum(grady.mul(grady)))[0];
    A(1, 2) = sum(sum(grady.mul(xIy_yIx)))[0];
    A(2, 2) = sum(sum(xIy_yIx.mul(xIy_yIx)))[0];
    A(1, 0) = A(0, 1);
    A(2, 0) = A(0, 2);
    A(2, 1) = A(1, 2);

    b(0) = -sum(sum(imgDiff.mul(gradx)))[0];
    b(1) = -sum(sum(imgDiff.mul(grady)))[0];
    b(2) = -sum(sum(imgDiff.mul(xIy_yIx)))[0];

    // Calculate parameters. We use Cholesky decomposition, as A is symmetric.
    Vec<double, 3> k = A.inv(DECOMP_CHOLESKY)*b;

    double cosT = cos(k(2));
    double sinT = sin(k(2));
    Matx<double, 2, 2> linTr(cosT, -sinT, sinT, cosT);
    Vec<double, 2> shift(k(0), k(1));

    if(res.empty()) {
        res = Ptr<Map>(new MapAffine(linTr, shift));
    } else {
        MapAffine newTr(linTr, shift);
        res->compose(newTr);
   }
}

////////////////////////////////////////////////////////////////////////////////////////////////////
cv::Ptr<Map> MapperGradEuclid::getMap(void) const
{
    return cv::Ptr<Map>(new MapAffine());
}


}}  // namespace cv::reg
