/*M///////////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2013, Alfonso Sanchez-Beato, all rights reserved.
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#include "precomp.hpp"
#include "opencv2/reg/mappergradsimilar.hpp"
#include "opencv2/reg/mapaffine.hpp"

namespace cv {
namespace reg {


////////////////////////////////////////////////////////////////////////////////////////////////////
MapperGradSimilar::MapperGradSimilar()
{
}


////////////////////////////////////////////////////////////////////////////////////////////////////
MapperGradSimilar::~MapperGradSimilar()
{
}


////////////////////////////////////////////////////////////////////////////////////////////////////
cv::Ptr<Map> MapperGradSimilar::calculate(
    InputArray _img1, InputArray image2, cv::Ptr<Map> init) const
{
    Mat img1 = _img1.getMat();
    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(!init.empty()) {
        // We have initial values for the registration: we move img2 to that initial reference
        init->inverseWarp(image2, img2);
    } else {
        img2 = image2.getMat();
    }

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

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

    // Calculate parameters using least squares
    Matx<double, 4, 4> A;
    Vec<double, 4> 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 xIx_p_yIy = grid_c.mul(gradx);
    xIx_p_yIy += grid_r.mul(grady);
    Mat yIx_m_xIy = grid_r.mul(gradx);
    yIx_m_xIy -= grid_c.mul(grady);

    A(0, 0) = sum(sum(sqr(xIx_p_yIy)))[0];
    A(0, 1) = sum(sum(xIx_p_yIy.mul(yIx_m_xIy)))[0];
    A(0, 2) = sum(sum(gradx.mul(xIx_p_yIy)))[0];
    A(0, 3) = sum(sum(grady.mul(xIx_p_yIy)))[0];

    A(1, 1) = sum(sum(sqr(yIx_m_xIy)))[0];
    A(1, 2) = sum(sum(gradx.mul(yIx_m_xIy)))[0];
    A(1, 3) = sum(sum(grady.mul(yIx_m_xIy)))[0];

    A(2, 2) = sum(sum(sqr(gradx)))[0];
    A(2, 3) = sum(sum(gradx.mul(grady)))[0];

    A(3, 3) = sum(sum(sqr(grady)))[0];

    // Lower half values (A is symmetric)
    A(1, 0) = A(0, 1);
    A(2, 0) = A(0, 2);
    A(3, 0) = A(0, 3);

    A(2, 1) = A(1, 2);
    A(3, 1) = A(1, 3);

    A(3, 2) = A(2, 3);

    // Calculation of b
    b(0) = -sum(sum(imgDiff.mul(xIx_p_yIy)))[0];
    b(1) = -sum(sum(imgDiff.mul(yIx_m_xIy)))[0];
    b(2) = -sum(sum(imgDiff.mul(gradx)))[0];
    b(3) = -sum(sum(imgDiff.mul(grady)))[0];

    // Calculate affine transformation. We use Cholesky decomposition, as A is symmetric.
    Vec<double, 4> k = A.inv(DECOMP_CHOLESKY)*b;

    Matx<double, 2, 2> linTr(k(0) + 1., k(1), -k(1), k(0) + 1.);
    Vec<double, 2> shift(k(2), k(3));
    if(init.empty()) {
        return Ptr<Map>(new MapAffine(linTr, shift));
    } else {
        Ptr<MapAffine> newTr(new MapAffine(linTr, shift));
        MapAffine* initPtr = dynamic_cast<MapAffine*>(init.get());
        Ptr<MapAffine> oldTr(new MapAffine(initPtr->getLinTr(), initPtr->getShift()));
        oldTr->compose(newTr);
        return oldTr;
   }
}

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


}}  // namespace cv::reg
