image transformation by homography matrix in C++ using OpenCV (warpPerspective)

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C++

OpenCV

image-processing

Hello

I'm trying perspective transformation of an image using homography matrix.

Given translation and rotation, I made a homography matrix and applied to the perspective transformation as:

Mat srcImg = imread("tests/image3.jp2", IMREAD_COLOR);
Mat dstImg, H;

Get_Homography(H, srcImg.size());

warpPerspective(srcImg, dstImg, H, dstImg.size());

imshow("output", dstImg);

#define FL_x 1000.0
#define FL_y 1000.0
void Get_Homography(Mat &H_out, cv::Size size)
{
    static float H_uc[9], C[9], C_inv[9], H[9], C_inv_H_uc[9];
    static float H33[3][3];
    static float R[9];
    static float T[3];
    static float n[3];
    static float d;
    static float nTd[9];
    static float phi, the, psi;

    n[0] = n[1] = 0.0;
    n[2] = -1.0;

    T[0] = -500;
    T[1] = -500;
    T[2] = 0.0;

    d = 100.0;

    phi = 0.0*D2R;
    the = 0.0*D2R;
    psi = 0.0*D2R;

    matMult(T, n, 3, 1, 3, nTd);
    matMult(nTd, &d, 9, 1, 1, nTd);

    getDCM_I2B(phi, the, psi, R);

    matAdd(R, nTd, 3, 3, H_uc);

    C[0] = FL_x;    C[1] = 0.0;     C[2] = size.width / 2.0;
    C[3] = 0.0;     C[4] = FL_y;    C[5] = size.height / 2.0;
    C[6] = 0.0;     C[7] = 0.0;     C[8] = 1.0;

    matInv33(C, C_inv);

    matMult(C_inv, H_uc, 3, 3, 3, C_inv_H_uc);
    matMult(C_inv_H_uc, C, 3, 3, 3, H);

    H33[0][0] = H[0];
    H33[0][1] = H[1];
    H33[0][2] = H[2];
    H33[1][0] = H[3];
    H33[1][1] = H[4];
    H33[1][2] = H[5];
    H33[2][0] = H[6];
    H33[2][1] = H[7];
    H33[2][2] = H[8];

    H_out = Mat(3, 3, CV_32F, H33);

    return;

}

Rotations by z-axis (any value at "psi") work alright.

But when I put any value (even 1.0 deg) to "the" or "phi", the resultant image is awkward. I cannot recognize what it is.

And when I put [-500, -500, 0] to T (translation), it produces shifted image as if it is taken in different position (shifted in right direction), but I think -500 -500 are too big. For d = 1.0, the resultant image just shows few pixel shift (not recognizably).

I thought my implementation of constructing homography matrix is right, but the results are awkward.

Could you give me some advice on this?

Thank you.