Function ComputeDerivatives

cpp/5_Domain_Specific/HSOpticalFlow/flowGold.cpp:225–267

////////////////////////////////////////////////////////////////////////// \brief computes image derivatives for a pair of images \param[in] I0 source image \param[in] I1 tracked image \param[in] w images width \param[in] h images height \param[in] s images stride \param[out] Ix x derivative \param[out] Iy y derivative \param[out] Iz temporal derivative ////////////////////////////

/// \param[out] Iz  temporal derivative
///////////////////////////////////////////////////////////////////////////////
static void ComputeDerivatives(const float *I0, const float *I1, int w, int h, int s, float *Ix, float *Iy, float *Iz)
{
    for (int i = 0; i < h; ++i) {
        for (int j = 0; j < w; ++j) {
            const int pos = j + i * s;
            float     t0, t1;
            // derivative filter is (1, -8, 0, 8, -1)/12
            // x derivative
            t0 = Tex2Di(I0, w, h, s, j - 2, i);
            t0 -= Tex2Di(I0, w, h, s, j - 1, i) * 8.0f;
            t0 += Tex2Di(I0, w, h, s, j + 1, i) * 8.0f;
            t0 -= Tex2Di(I0, w, h, s, j + 2, i);
            t0 /= 12.0f;

            t1 = Tex2Di(I1, w, h, s, j - 2, i);
            t1 -= Tex2Di(I1, w, h, s, j - 1, i) * 8.0f;
            t1 += Tex2Di(I1, w, h, s, j + 1, i) * 8.0f;
            t1 -= Tex2Di(I1, w, h, s, j + 2, i);
            t1 /= 12.0f;

            // spatial derivatives are averaged
            Ix[pos] = (t0 + t1) * 0.5f;

            // t derivative
            Iz[pos] = I1[pos] - I0[pos];

            // y derivative
            t0 = Tex2Di(I0, w, h, s, j, i - 2);
            t0 -= Tex2Di(I0, w, h, s, j, i - 1) * 8.0f;
            t0 += Tex2Di(I0, w, h, s, j, i + 1) * 8.0f;
            t0 -= Tex2Di(I0, w, h, s, j, i + 2);
            t0 /= 12.0f;

            t1 = Tex2Di(I1, w, h, s, j, i - 2);
            t1 -= Tex2Di(I1, w, h, s, j, i - 1) * 8.0f;
            t1 += Tex2Di(I1, w, h, s, j, i + 1) * 8.0f;
            t1 -= Tex2Di(I1, w, h, s, j, i + 2);
            t1 /= 12.0f;

            Iy[pos] = (t0 + t1) * 0.5f;
        }
    }
}

///////////////////////////////////////////////////////////////////////////////
/// \brief one iteration of classical Horn-Schunck method