sobel() [2/2]

MAYAFLUX_API GradientResult MayaFlux::Kinesis::Vision::sobel	(	std::span< const float >	gray,
		uint32_t	w,
		uint32_t	h
	)

Sobel gradient operator.

3x3 Sobel kernels applied separably. dx and dy are in [-1, 1]. Magnitude is normalised by the theoretical maximum (4 * 255 / 255 = 4 for uint8 sources, but since input is already [0,1] the max magnitude is sqrt(2) which is divided out). Angle via atan2(dy, dx).

Parameters

gray	Single-channel float span, size must be w * h.
w	Image width in pixels.
h	Image height in pixels.

Returns

GradientResult with all four maps populated.

Definition at line 72 of file Gradient.cpp.

{
    const size_t n = static_cast<size_t>(w) * h;
    GradientResult r;
    r.dx.resize(n);
    r.dy.resize(n);
    std::vector<float> tmp(n);
    sobel(gray, r.dx, r.dy, tmp, w, h);
 
    const auto en = static_cast<Eigen::Index>(n);
    auto dx = Eigen::Map<const Eigen::ArrayXf>(r.dx.data(), en);
    auto dy = Eigen::Map<const Eigen::ArrayXf>(r.dy.data(), en);
    r.magnitude.resize(n);
    r.angle.resize(n);
 
    Eigen::Map<Eigen::ArrayXf>(r.magnitude.data(), en) = (dx.square() + dy.square()).sqrt();
    const float peak = Eigen::Map<const Eigen::ArrayXf>(r.magnitude.data(), en).maxCoeff();
    if (peak > 0.0F)
        Eigen::Map<Eigen::ArrayXf>(r.magnitude.data(), en) /= peak;
 
    std::transform(std::execution::par_unseq, r.dx.begin(), r.dx.end(), r.dy.begin(), r.angle.begin(),
        [](float gx, float gy) { return std::atan2(gy, gx); });
    return r;
}

References MayaFlux::Kinesis::Vision::GradientResult::angle, MayaFlux::Kinesis::Vision::GradientResult::dx, MayaFlux::Kinesis::Vision::GradientResult::dy, h, MayaFlux::Kinesis::Vision::GradientResult::magnitude, and sobel().

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