canny边缘检测C\C++实现

这个是主函数

#define PI              3.1415926#define EDGE_VALUE      235#define NON_EDGE_VALUE  16typedef unsigned char uint8;enum {HOR = 0, VER, POS45, NEG45};const int row_table[4] = {0, 1, 1, 1};const int col_table[4] = {1, 0, 1, -1};void CannyEdge(const uint8* img, int width, int height, int pitch, int low_thr, int high_thr, uint8 *edge){uint8 *lpf_img = new uint8[pitch * height];int *grad = new int[pitch * height];int *max_grad = new int[pitch * height];GaussianFilter(img, width, height, pitch, lpf_img);CalcGrad(lpf_img, width, height, pitch, grad);SuppressNonMax(grad, width, height, pitch, max_grad);GetEdge(max_grad, width, height, pitch, low_thr, high_thr, edge);delete [] lpf_img;delete [] grad;delete [] max_grad;}

对图像做高斯低通滤波，这里用一个7tap的滤波器，滤波器尺寸可以根据需要做调整

二维高斯滤波可以分解成两个一维的高斯滤波，先做水平滤波，再做垂直滤波

void GaussianFilter(const uint8* srcp, int width, int height, int pitch, uint8 *dstp){int filter[7] = {1, 6, 19, 27, 19, 6, 1};int weight_sum = 79;int *fltp = filter + 3;uint8 *midp = new uint8[pitch * height];memcpy(dstp, srcp, pitch * height);memcpy(midp, srcp, pitch * height);// hor filterfor(int ver = 0; ver < height; ++ver) {for(int hor = radius; hor < width - radius; ++hor) {int sum = 0;for(int x = -radius; x <= radius; ++x) {sum += srcp[ver * pitch + hor + x] * fltp[x];}midp[ver * pitch + hor] = sum / weight_sum;}}// ver filterfor(int ver = radius; ver < height - radius; ++ver) {for(int hor = 0; hor < width; ++hor) {int sum = 0;for(int y = -radius; y <= radius; ++y) {sum += midp[(ver + y) * pitch + hor] * fltp[y];}dstp[ver * pitch + hor] = sum / weight_sum;}}delete [] midp;}

计算梯度值和法线方向

void CalcGrad(uint8 *img, int width, int height, int pitch, int *grad){const double tan225 = tan(PI / 8);const double tan675 = tan(PI * 3 / 8);memset((void*)grad, 0, pitch * height * sizeof(int));for(int ver = 0; ver < height - 1; ++ver) {for(int hor = 0; hor < width - 1; ++hor) {int offset = ver * pitch + hor;int diff_x = img[offset + 1] - img[offset];int diff_y = img[offset + pitch] - img[offset];int dir;double tanv = diff_y / (diff_x + 0.0001);if(tanv < tan225 && tanv >= -tan225) dir = HOR;else if(tanv < tan675 && tanv >= tan225)  dir = POS45;else if(tanv < -tan675 || tanv >= tan675) dir = VER;else dir = NEG45;int gradient = (int)sqrt(double(diff_x * diff_x + diff_y * diff_y) );grad[offset] = (gradient << 2) + dir; // 低2位放方向，高位放梯度值}}}

非最大值抑制

void SuppressNonMax(int *grad, int width, int height, int pitch, int *max_grad){memset((void*)max_grad, 0, pitch * height * sizeof(int));for(int ver = 1; ver < height - 1; ++ver) {for(int hor = 1; hor < width - 1; ++hor) {int offset = ver * pitch + hor;int dir = grad[offset] & 0x3;int row = row_table[dir];int col = col_table[dir];int offset1 = (ver + row) * pitch + hor + col;int offset2 = (ver - row) * pitch + hor - col;int grad0 = grad[offset] >> 2;int grad1 = grad[offset1] >> 2;int grad2 = grad[offset2] >> 2;if(grad0 >= grad1 && grad0 >= grad2) {max_grad[offset] = grad0;}}}}

利用双阈值得到边缘，连接线

阈值可以根据需要进行设置，这里设置low_thr = 7，high_thr = 14

void GetEdge(int *max_grad, int width, int height, int pitch, int low_thres, int high_thres, uint8 *edge){memset(edge, NON_EDGE_VALUE, pitch * height);for(int ver = 1; ver < height-1; ++ver) {for(int hor = 1; hor < width-1; ++hor) {int offset = ver * pitch + hor;if(max_grad[offset] >= high_thres) { edge[offset] = EDGE_VALUE;}else if(max_grad[offset] >= low_thres) {for(int row = -1; row <= 1; ++row) {for(int col = -1; col <= 1; ++col) {if(max_grad[(ver + row) * pitch + hor + col] >= high_thres) {edge[offset] = EDGE_VALUE;break;}}}}}}}

左边是原图，右边是得到的边缘