sobel_operator.h

#ifndef SOBEL_OPERATOR_H
#define SOBEL_OPERATOR_H
 
#ifdef __cplusplus
#include <cassert>
#include <cmath>
#include <iostream>
#include <utility>
#include <vector>
#include "../image.h"
#endif

namespace sobel {
inline std::pair<std::vector<std::vector<int32_t>>, std::vector<std::vector<int32_t>>> kernel() {
    std::vector<std::vector<int32_t>> G_x = {{1, 0, -1}, {2, 0, -2}, {1, 0, -1}};
    std::vector<std::vector<int32_t>> G_y = {{1, 2, 1}, {0, 0, 0}, {-1, -2, -1}};
    return std::make_pair(G_x, G_y);
}

inline std::vector<std::vector<int32_t>> square(const std::vector<std::vector<int32_t>>& G) {
    int height = G.size();
    int width = G[0].size();
    std::vector<std::vector<int32_t>> res_img(height, std::vector<int32_t>(width));
    for (int i = 0; i < height; i++) {
        for (int j = 0; j < width; j++) {
            res_img[i][j] = sqrt(G[i][j]);
        }
    }
    return res_img;
}

inline std::vector<std::vector<int32_t>> Sobel(const std::vector<std::vector<int32_t>>& image) {
    Image img(image);
 
    std::pair<std::vector<std::vector<int32_t>>, std::vector<std::vector<int32_t>>> kernels =
        kernel();
    std::vector<std::vector<int32_t>> k1 = kernels.first;
    std::vector<std::vector<int32_t>> k2 = kernels.second;
 
    Image G_x(img.apply_filter2d(k1));
    Image G_y(img.apply_filter2d(k2));
 
    G_x = G_x.mul(G_x);
    G_y = G_y.mul(G_y);
 
    Image G(G_x);   // G = G_x^2
    G = G.add(G_y); // G += G_y^2
 
    return square(G.get_2d_array()); // result is: G = sqrt(G_x^2 + G_y^2)
}
} // namespace sobel
 
#endif