【三维重建】特征点匹配
1、特征点
1.1 什么是角点
角点是图像中某些属性较为突出的像素点，例如像素值最大或者最小的点、线段的顶点、孤立的边缘点等。
常见的角点：
- 灰度梯度的最大值对应的像素点
- 两条直线或者曲线的交点
- 一阶梯度的导数最大值和梯度方向变化率最大的像素点
- 一阶导数值最大，但是二阶导数值为0的像素点
1.2 什么是特征点：
特征点与角点在宏观定义上相同，都是能够表现图像中局部特征的像素点，但是特征点区别于角点的是其具有能够唯一描述像素点特征的描述子。
通常特征点由关键点和描述子组成。
如：SIFT特征点、ORB特征点等都需要先计算关键点坐标再计算描述子。
关键点：KeyPoint类，可以存放关键点的坐标、方向等相关数据。
描述子：用来唯一描述关键点的一串数字，与每个人的个人信息类似，通过描述子可以区分两个不同的关键点，也可以在不同的图像中寻找同一个关键点。
1.3 特征点检测
SIFT特征点检测、SURF特征点检测、ORB特征点检测
1.4 特征点匹配
特征点匹配就是在不同的图像中寻找同一物体的同一特征点。
每个特征点具有标志着唯一身份和特点的描述子，所以特征点匹配就是在两个图像中寻找具有相似描述子的两个特征点。
寻找两个相似描述子的方法：
- 第一类：计算两个描述子之间的欧式距离，这种匹配方式的特征点有SIFT特征点、SURF特征点等
- 第二类：计算两个描述子之间的汉明距离，这种匹配方式的特征点有ORB特征点、BRISK特征点等
特征点匹配是图像处理领域寻找不同图像间信息关联的重要方法。由于相机移动导致成像视场发生改变，因此同一个物体会出现在图像中不同的位置，通过特征点匹配可以快速定位物体在新图像中的位置，为后续对图像的进一步处理提供数据支持。
特征点匹配由于数据量小、匹配精确而被广泛应用在三维重建、视觉定位、运动估计、图像配准等领域。
1.5 orb特征点匹配的例子(来源于slam十四讲)
#include <iostream>
#include <opencv2/core/core.hpp>
#include <opencv2/features2d/features2d.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <chrono>
using namespace std;
using namespace cv;
int main(int argc, char *argv[])
{
// if (argc != 3)
// {
// cout << "usage: ch7_orb_cv img1 img2" << endl;
// }
argv[1] = (char *)"../1.png";
argv[2] = (char *)"../2.png";
// 读取图像
Mat img_1 = imread(argv[1]);
Mat img_2 = imread(argv[2]);
assert(img_1.data != nullptr && img_2.data != nullptr);
// 初始化
std::vector<KeyPoint> keypoints_1, keypoints_2;
Mat descriptors_1, descriptors_2;
Ptr<FeatureDetector> detector = ORB::create();
Ptr<DescriptorExtractor> descriptor = ORB::create();
Ptr<DescriptorMatcher> matcher = DescriptorMatcher::create("BruteForce-Hamming");
// --第一步：检测 Oriented FAST 角点位置
chrono::steady_clock::time_point t1 = chrono::steady_clock::now();
detector->detect(img_1, keypoints_1);
detector->detect(img_2, keypoints_2);
// --第二步：根据角点位置计算 BRIEF 描述子
descriptor->compute(img_1, keypoints_1, descriptors_1);
descriptor->compute(img_2, keypoints_2, descriptors_2);
chrono::steady_clock::time_point t2 = chrono::steady_clock::now();
chrono::duration<double> time_used = chrono::duration_cast<chrono::duration<double>>(t2 - t1);
cout << "extract ORB cost = " << time_used.count() << " seconds." << endl;
Mat outimg1;
drawKeypoints(img_1, keypoints_1, outimg1, Scalar::all(-1), DrawMatchesFlags::DEFAULT);
imshow("ORB features", outimg1);
// -- 第三步：对两幅图像中的BRIEF描述子进行匹配，使用 Hamming 距离
vector<DMatch> matches;
t1 = chrono::steady_clock::now();
matcher->match(descriptors_1, descriptors_2, matches);
t2 = chrono::steady_clock::now();
time_used = chrono::duration_cast<chrono::duration<double>>(t2 - t1);
cout << "match ORB cost = " << time_used.count() << " seconds." << endl;
// -- 第四步：匹配点对筛选
// 计算最小距离和最大距离
auto min_max = minmax_element(matches.begin(), matches.end(),
[](const DMatch &m1, const DMatch &m2)
{ return m1.distance < m2.distance; });
double min_dist = min_max.first->distance;
double max_dist = min_max.second->distance;
printf("-- Max dist : %f\n", max_dist);
printf("-- Min dist : %f\n", min_dist);
// 当描述子之间的距离大于两倍的最小距离时，即认为匹配有误，但有时候最小距离会非常小，设置一个经验值30作为下限
std::vector<DMatch> good_matches;
for (int i = 0; i < descriptors_1.rows; i++)
{
if (matches[i].distance <= max(2 * min_dist, 30.0))
{
good_matches.push_back(matches[i]);
}
}
// -- 第五步：绘制匹配结果
Mat img_match;
Mat img_goodmatch;
drawMatches(img_1, keypoints_1, img_2, keypoints_2, matches, img_match);
drawMatches(img_1, keypoints_1, img_2, keypoints_2, good_matches, img_goodmatch);
imshow("all matches", img_match);
imshow("good matches", img_goodmatch);
waitKey(0);
return 0;
}
手写ORB
#include <opencv2/opencv.hpp>
#include <string>
#include <nmmintrin.h>
using namespace std;
// global variables
string first_file = "../1.png";
string second_file = "../2.png";
// 32 bit unsigned int, will have 8, 8x32=256
typedef vector<uint32_t> DescType; // Descriptor type
/**
* compute descriptor of orb keypoints
* @param img input image
* @param keypoints detected fast keypoints
* @param descriptors descriptors
*
* NOTE: if a keypoint goes outside the image boundary (8 pixels),
* descriptors will not be compute and will be left as empty
*/
void ComputeORB(const cv::Mat &img, vector<cv::KeyPoint> &keypoints, vector<DescType> &descriptors);
/**
* brute-force match two sets of descriptors
* @param desc1 the first descriptor
* @param desc2 the second descriptor
* @param matches matches of two images
*/
void BfMatch(const vector<DescType> &desc1, const vector<DescType> &desc2, vector<cv::DMatch> &matches);
int main(int argc, char *argv[])
{
// load iamge,灰度图
cv::Mat first_image = cv::imread(first_file, 0);
cv::Mat second_image = cv::imread(second_file, 0);
assert(first_image.data != nullptr && second_image.data != nullptr);
// detect FAST keypoints1 using threshold=40
// 这边的阈值40就是十四讲中P155，FAST关键点中提到的第二步：设置一个阈值T
// 这边的阈值是什么意思呢，因为FAST是一种角点，主要检测局部像素灰度变化明显的地方，
// 然后需要比较中间点和领域像素亮度的差异
chrono::steady_clock::time_point t1 = chrono::steady_clock::now();
vector<cv::KeyPoint> keypoints1;
cv::FAST(first_image, keypoints1, 40);
vector<DescType> descriptor1;
ComputeORB(first_image, keypoints1, descriptor1);
// same for the second
vector<cv::KeyPoint> keypoints2;
vector<DescType> descriptor2;
cv::FAST(second_image, keypoints2, 40);
ComputeORB(second_image, keypoints2, descriptor2);
chrono::steady_clock::time_point t2 = chrono::steady_clock::now();
chrono::duration<double> time_used = chrono::duration_cast<chrono::duration<double>>(t2 - t1);
cout << "extract ORB cost = " << time_used.count() << "seconds. " << endl;
// find matches
vector<cv::DMatch> matches;
t1 = chrono::steady_clock::now();
BfMatch(descriptor1, descriptor2, matches);
t2 = chrono::steady_clock::now();
time_used = chrono::duration_cast<chrono::duration<double>>(t2 - t1);
cout << "match ORB cost = " << time_used.count() << " seconds." << endl;
cout << "matches : " << matches.size() << endl;
// plot the matches
cv::Mat image_show;
cv::drawMatches(first_image, keypoints1, second_image, keypoints2, matches, image_show);
cv::imshow("matches", image_show);
cv::waitKey(0);
return 0;
}
// -------------------------------------------------------------------------------------------------- //
// ORB pattern
int ORB_pattern[256 * 4] = {
8, -3, 9, 5 /*mean (0), correlation (0)*/,
4, 2, 7, -12 /*mean (1.12461e-05), correlation (0.0437584)*/,
-11, 9, -8, 2 /*mean (3.37382e-05), correlation (0.0617409)*/,
7, -12, 12, -13 /*mean (5.62303e-05), correlation (0.0636977)*/,
2, -13, 2, 12 /*mean (0.000134953), correlation (0.085099)*/,
1, -7, 1, 6 /*mean (0.000528565), correlation (0.0857175)*/,
-2, -10, -2, -4 /*mean (0.0188821), correlation (0.0985774)*/,
-13, -13, -11, -8 /*mean (0.0363135), correlation (0.0899616)*/,
-13, -3, -12, -9 /*mean (0.121806), correlation (0.099849)*/,
10, 4, 11, 9 /*mean (0.122065), correlation (0.093285)*/,
-13, -8, -8, -9 /*mean (0.162787), correlation (0.0942748)*/,
-11, 7, -9, 12 /*mean (0.21561), correlation (0.0974438)*/,
7, 7, 12, 6 /*mean (0.160583), correlation (0.130064)*/,
-4, -5, -3, 0 /*mean (0.228171), correlation (0.132998)*/,
-13, 2, -12, -3 /*mean (0.00997526), correlation (0.145926)*/,
-9, 0, -7, 5 /*mean (0.198234), correlation (0.143636)*/,
12, -6, 12, -1 /*mean (0.0676226), correlation (0.16689)*/,
-3, 6, -2, 12 /*mean (0.166847), correlation (0.171682)*/,
-6, -13, -4, -8 /*mean (0.101215), correlation (0.179716)*/,
11, -13, 12, -8 /*mean (0.200641), correlation (0.192279)*/,
4, 7, 5, 1 /*mean (0.205106), correlation (0.186848)*/,
5, -3, 10, -3 /*mean (0.234908), correlation (0.192319)*/,
3, -7, 6, 12 /*mean (0.0709964), correlation (0.210872)*/,
-8, -7, -6, -2 /*mean (0.0939834), correlation (0.212589)*/,
-2, 11, -1, -10 /*mean (0.127778), correlation (0.20866)*/,
-13, 12, -8, 10 /*mean (0.14783), correlation (0.206356)*/,
-7, 3, -5, -3 /*mean (0.182141), correlation (0.198942)*/,
-4, 2, -3, 7 /*mean (0.188237), correlation (0.21384)*/,
-10, -12, -6, 11 /*mean (0.14865), correlation (0.23571)*/,
5, -12, 6, -7 /*mean (0.222312), correlation (0.23324)*/,
5, -6, 7, -1 /*mean (0.229082), correlation (0.23389)*/,
1, 0, 4, -5 /*mean (0.241577), correlation (0.215286)*/,
9, 11, 11, -13 /*mean (0.00338507), correlation (0.251373)*/,
4, 7, 4, 12 /*mean (0.131005), correlation (0.257622)*/,
2, -1, 4, 4 /*mean (0.152755), correlation (0.255205)*/,
-4, -12, -2, 7 /*mean (0.182771), correlation (0.244867)*/,
-8, -5, -7, -10 /*mean (0.186898), correlation (0.23901)*/,
4, 11, 9, 12 /*mean (0.226226), correlation (0.258255)*/,
0, -8, 1, -13 /*mean (0.0897886), correlation (0.274827)*/,
-13, -2, -8, 2 /*mean (0.148774), correlation (0.28065)*/,
-3, -2, -2, 3 /*mean (0.153048), correlation (0.283063)*/,
-6, 9, -4, -9 /*mean (0.169523), correlation (0.278248)*/,
8, 12, 10, 7 /*mean (0.225337), correlation (0.282851)*/,
0, 9, 1, 3 /*mean (0.226687), correlation (0.278734)*/,
7, -5, 11, -10 /*mean (0.00693882), correlation (0.305161)*/,
-13, -6, -11, 0 /*mean (0.0227283), correlation (0.300181)*/,
10, 7, 12, 1 /*mean (0.125517), correlation (0.31089)*/,
-6, -3, -6, 12 /*mean (0.131748), correlation (0.312779)*/,
10, -9, 12, -4 /*mean (0.144827), correlation (0.292797)*/,
-13, 8, -8, -12 /*mean (0.149202), correlation (0.308918)*/,
-13, 0, -8, -4 /*mean (0.160909), correlation (0.310013)*/,
3, 3, 7, 8 /*mean (0.177755), correlation (0.309394)*/,
5, 7, 10, -7 /*mean (0.212337), correlation (0.310315)*/,
-1, 7, 1, -12 /*mean (0.214429), correlation (0.311933)*/,
3, -10, 5, 6 /*mean (0.235807), correlation (0.313104)*/,
2, -4, 3, -10 /*mean (0.00494827), correlation (0.344948)*/,
-13, 0, -13, 5 /*mean (0.0549145), correlation (0.344675)*/,
-13, -7, -12, 12 /*mean (0.103385), correlation (0.342715)*/,
-13, 3, -11, 8 /*mean (0.134222), correlation (0.322922)*/,
-7, 12, -4, 7 /*mean (0.153284), correlation (0.337061)*/,
6, -10, 12, 8 /*mean (0.154881), correlation (0.329257)*/,
-9, -1, -7, -6 /*mean (0.200967), correlation (0.33312)*/,
-2, -5, 0, 12 /*mean (0.201518), correlation (0.340635)*/,
-12, 5, -7, 5 /*mean (0.207805), correlation (0.335631)*/,
3, -10, 8, -13 /*mean (0.224438), correlation (0.34504)*/,
-7, -7, -4, 5 /*mean (0.239361), correlation (0.338053)*/,
-3, -2, -1, -7 /*mean (0.240744), correlation (0.344322)*/,
2, 9, 5, -11 /*mean (0.242949), correlation (0.34145)*/,
-11, -13, -5, -13 /*mean (0.244028), correlation (0.336861)*/,
-1, 6, 0, -1 /*mean (0.247571), correlation (0.343684)*/,
5, -3, 5, 2 /*mean (0.000697256), correlation (0.357265)*/,
-4, -13, -4, 12 /*mean (0.00213675), correlation (0.373827)*/,
-9, -6, -9, 6 /*mean (0.0126856), correlation (0.373938)*/,
-12, -10, -8, -4 /*mean (0.0152497), correlation (0.364237)*/,
10, 2, 12, -3 /*mean (0.0299933), correlation (0.345292)*/,
7, 12, 12, 12 /*mean (0.0307242), correlation (0.366299)*/,
-7, -13, -6, 5 /*mean (0.0534975), correlation (0.368357)*/,
-4, 9, -3, 4 /*mean (0.099865), correlation (0.372276)*/,
7, -1, 12, 2 /*mean (0.117083), correlation (0.364529)*/,
-7, 6, -5, 1 /*mean (0.126125), correlation (0.369606)*/,
-13, 11, -12, 5 /*mean (0.130364), correlation (0.358502)*/,
-3, 7, -2, -6 /*mean (0.131691), correlation (0.375531)*/,
7, -8, 12, -7 /*mean (0.160166), correlation (0.379508)*/,
-13, -7, -11, -12 /*mean (0.167848), correlation (0.353343)*/,
1, -3, 12, 12 /*mean (0.183378), correlation (0.371916)*/,
2, -6, 3, 0 /*mean (0.228711), correlation (0.371761)*/,
-4, 3, -2, -13 /*mean (0.247211), correlation (0.364063)*/,
-1, -13, 1, 9 /*mean (0.249325), correlation (0.378139)*/,
7, 1, 8, -6 /*mean (0.000652272), correlation (0.411682)*/,
1, -1, 3, 12 /*mean (0.00248538), correlation (0.392988)*/,
9, 1, 12, 6 /*mean (0.0206815), correlation (0.386106)*/,
-1, -9, -1, 3 /*mean (0.0364485), correlation (0.410752)*/,
-13, -13, -10, 5 /*mean (0.0376068), correlation (0.398374)*/,
7, 7, 10, 12 /*mean (0.0424202), correlation (0.405663)*/,
12, -5, 12, 9 /*mean (0.0942645), correlation (0.410422)*/,
6, 3, 7, 11 /*mean (0.1074), correlation (0.413224)*/,
5, -13, 6, 10 /*mean (0.109256), correlation (0.408646)*/,
2, -12, 2, 3 /*mean (0.131691), correlation (0.416076)*/,
3, 8, 4, -6 /*mean (0.165081), correlation (0.417569)*/,
2, 6, 12, -13 /*mean (0.171874), correlation (0.408471)*/,
9, -12, 10, 3 /*mean (0.175146), correlation (0.41296)*/,
-8, 4, -7, 9 /*mean (0.183682), correlation (0.402956)*/,
-11, 12, -4, -6 /*mean (0.184672), correlation (0.416125)*/,
1, 12, 2, -8 /*mean (0.191487), correlation (0.386696)*/,
6, -9, 7, -4 /*mean (0.192668), correlation (0.394771)*/,
2, 3, 3, -2 /*mean (0.200157), correlation (0.408303)*/,
6, 3, 11, 0 /*mean (0.204588), correlation (0.411762)*/,
3, -3, 8, -8 /*mean (0.205904), correlation (0.416294)*/,
7, 8, 9, 3 /*mean (0.213237), correlation (0.409306)*/,
-11, -5, -6, -4 /*mean (0.243444), correlation (0.395069)*/,
-10, 11, -5, 10 /*mean (0.247672), correlation (0.413392)*/,
-5, -8, -3, 12 /*mean (0.24774), correlation (0.411416)*/,
-10, 5, -9, 0 /*mean (0.00213675), correlation (0.454003)*/,
8, -1, 12, -6 /*mean (0.0293635), correlation (0.455368)*/,
4, -6, 6, -11 /*mean (0.0404971), correlation (0.457393)*/,
-10, 12, -8, 7 /*mean (0.0481107), correlation (0.448364)*/,
4, -2, 6, 7 /*mean (0.050641), correlation (0.455019)*/,
-2, 0, -2, 12 /*mean (0.0525978), correlation (0.44338)*/,
-5, -8, -5, 2 /*mean (0.0629667), correlation (0.457096)*/,
7, -6, 10, 12 /*mean (0.0653846), correlation (0.445623)*/,
-9, -13, -8, -8 /*mean (0.0858749), correlation (0.449789)*/,
-5, -13, -5, -2 /*mean (0.122402), correlation (0.450201)*/,
8, -8, 9, -13 /*mean (0.125416), correlation (0.453224)*/,
-9, -11, -9, 0 /*mean (0.130128), correlation (0.458724)*/,
1, -8, 1, -2 /*mean (0.132467), correlation (0.440133)*/,
7, -4, 9, 1 /*mean (0.132692), correlation (0.454)*/,
-2, 1, -1, -4 /*mean (0.135695), correlation (0.455739)*/,
11, -6, 12, -11 /*mean (0.142904), correlation (0.446114)*/,
-12, -9, -6, 4 /*mean (0.146165), correlation (0.451473)*/,
3, 7, 7, 12 /*mean (0.147627), correlation (0.456643)*/,
5, 5, 10, 8 /*mean (0.152901), correlation (0.455036)*/,
0, -4, 2, 8 /*mean (0.167083), correlation (0.459315)*/,
-9, 12, -5, -13 /*mean (0.173234), correlation (0.454706)*/,
0, 7, 2, 12 /*mean (0.18312), correlation (0.433855)*/,
-1, 2, 1, 7 /*mean (0.185504), correlation (0.443838)*/,
5, 11, 7, -9 /*mean (0.185706), correlation (0.451123)*/,
3, 5, 6, -8 /*mean (0.188968), correlation (0.455808)*/,
-13, -4, -8, 9 /*mean (0.191667), correlation (0.459128)*/,
-5, 9, -3, -3 /*mean (0.193196), correlation (0.458364)*/,
-4, -7, -3, -12 /*mean (0.196536), correlation (0.455782)*/,
6, 5, 8, 0 /*mean (0.1972), correlation (0.450481)*/,
-7, 6, -6, 12 /*mean (0.199438), correlation (0.458156)*/,
-13, 6, -5, -2 /*mean (0.211224), correlation (0.449548)*/,
1, -10, 3, 10 /*mean (0.211718), correlation (0.440606)*/,
4, 1, 8, -4 /*mean (0.213034), correlation (0.443177)*/,
-2, -2, 2, -13 /*mean (0.234334), correlation (0.455304)*/,
2, -12, 12, 12 /*mean (0.235684), correlation (0.443436)*/,
-2, -13, 0, -6 /*mean (0.237674), correlation (0.452525)*/,
4, 1, 9, 3 /*mean (0.23962), correlation (0.444824)*/,
-6, -10, -3, -5 /*mean (0.248459), correlation (0.439621)*/,
-3, -13, -1, 1 /*mean (0.249505), correlation (0.456666)*/,
7, 5, 12, -11 /*mean (0.00119208), correlation (0.495466)*/,
4, -2, 5, -7 /*mean (0.00372245), correlation (0.484214)*/,
-13, 9, -9, -5 /*mean (0.00741116), correlation (0.499854)*/,
7, 1, 8, 6 /*mean (0.0208952), correlation (0.499773)*/,
7, -8, 7, 6 /*mean (0.0220085), correlation (0.501609)*/,
-7, -4, -7, 1 /*mean (0.0233806), correlation (0.496568)*/,
-8, 11, -7, -8 /*mean (0.0236505), correlation (0.489719)*/,
-13, 6, -12, -8 /*mean (0.0268781), correlation (0.503487)*/,
2, 4, 3, 9 /*mean (0.0323324), correlation (0.501938)*/,
10, -5, 12, 3 /*mean (0.0399235), correlation (0.494029)*/,
-6, -5, -6, 7 /*mean (0.0420153), correlation (0.486579)*/,
8, -3, 9, -8 /*mean (0.0548021), correlation (0.484237)*/,
2, -12, 2, 8 /*mean (0.0616622), correlation (0.496642)*/,
-11, -2, -10, 3 /*mean (0.0627755), correlation (0.498563)*/,
-12, -13, -7, -9 /*mean (0.0829622), correlation (0.495491)*/,
-11, 0, -10, -5 /*mean (0.0843342), correlation (0.487146)*/,
5, -3, 11, 8 /*mean (0.0929937), correlation (0.502315)*/,
-2, -13, -1, 12 /*mean (0.113327), correlation (0.48941)*/,
-1, -8, 0, 9 /*mean (0.132119), correlation (0.467268)*/,
-13, -11, -12, -5 /*mean (0.136269), correlation (0.498771)*/,
-10, -2, -10, 11 /*mean (0.142173), correlation (0.498714)*/,
-3, 9, -2, -13 /*mean (0.144141), correlation (0.491973)*/,
2, -3, 3, 2 /*mean (0.14892), correlation (0.500782)*/,
-9, -13, -4, 0 /*mean (0.150371), correlation (0.498211)*/,
-4, 6, -3, -10 /*mean (0.152159), correlation (0.495547)*/,
-4, 12, -2, -7 /*mean (0.156152), correlation (0.496925)*/,
-6, -11, -4, 9 /*mean (0.15749), correlation (0.499222)*/,
6, -3, 6, 11 /*mean (0.159211), correlation (0.503821)*/,
-13, 11, -5, 5 /*mean (0.162427), correlation (0.501907)*/,
11, 11, 12, 6 /*mean (0.16652), correlation (0.497632)*/,
7, -5, 12, -2 /*mean (0.169141), correlation (0.484474)*/,
-1, 12, 0, 7 /*mean (0.169456), correlation (0.495339)*/,
-4, -8, -3, -2 /*mean (0.171457), correlation (0.487251)*/,
-7, 1, -6, 7 /*mean (0.175), correlation (0.500024)*/,
-13, -12, -8, -13 /*mean (0.175866), correlation (0.497523)*/,
-7, -2, -6, -8 /*mean (0.178273), correlation (0.501854)*/,
-8, 5, -6, -9 /*mean (0.181107), correlation (0.494888)*/,
-5, -1, -4, 5 /*mean (0.190227), correlation (0.482557)*/,
-13, 7, -8, 10 /*mean (0.196739), correlation (0.496503)*/,
1, 5, 5, -13 /*mean (0.19973), correlation (0.499759)*/,
1, 0, 10, -13 /*mean (0.204465), correlation (0.49873)*/,
9, 12, 10, -1 /*mean (0.209334), correlation (0.49063)*/,
5, -8, 10, -9 /*mean (0.211134), correlation (0.503011)*/,
-1, 11, 1, -13 /*mean (0.212), correlation (0.499414)*/,
-9, -3, -6, 2 /*mean (0.212168), correlation (0.480739)*/,
-1, -10, 1, 12 /*mean (0.212731), correlation (0.502523)*/,
-13, 1, -8, -10 /*mean (0.21327), correlation (0.489786)*/,
8, -11, 10, -6 /*mean (0.214159), correlation (0.488246)*/,
2, -13, 3, -6 /*mean (0.216993), correlation (0.50287)*/,
7, -13, 12, -9 /*mean (0.223639), correlation (0.470502)*/,
-10, -10, -5, -7 /*mean (0.224089), correlation (0.500852)*/,
-10, -8, -8, -13 /*mean (0.228666), correlation (0.502629)*/,
4, -6, 8, 5 /*mean (0.22906), correlation (0.498305)*/,
3, 12, 8, -13 /*mean (0.233378), correlation (0.503825)*/,
-4, 2, -3, -3 /*mean (0.234323), correlation (0.476692)*/,
5, -13, 10, -12 /*mean (0.236392), correlation (0.475462)*/,
4, -13, 5, -1 /*mean (0.236842), correlation (0.504132)*/,
-9, 9, -4, 3 /*mean (0.236977), correlation (0.497739)*/,
0, 3, 3, -9 /*mean (0.24314), correlation (0.499398)*/,
-12, 1, -6, 1 /*mean (0.243297), correlation (0.489447)*/,
3, 2, 4, -8 /*mean (0.00155196), correlation (0.553496)*/,
-10, -10, -10, 9 /*mean (0.00239541), correlation (0.54297)*/,
8, -13, 12, 12 /*mean (0.0034413), correlation (0.544361)*/,
-8, -12, -6, -5 /*mean (0.003565), correlation (0.551225)*/,
2, 2, 3, 7 /*mean (0.00835583), correlation (0.55285)*/,
10, 6, 11, -8 /*mean (0.00885065), correlation (0.540913)*/,
6, 8, 8, -12 /*mean (0.0101552), correlation (0.551085)*/,
-7, 10, -6, 5 /*mean (0.0102227), correlation (0.533635)*/,
-3, -9, -3, 9 /*mean (0.0110211), correlation (0.543121)*/,
-1, -13, -1, 5 /*mean (0.0113473), correlation (0.550173)*/,
-3, -7, -3, 4 /*mean (0.0140913), correlation (0.554774)*/,
-8, -2, -8, 3 /*mean (0.017049), correlation (0.55461)*/,
4, 2, 12, 12 /*mean (0.01778), correlation (0.546921)*/,
2, -5, 3, 11 /*mean (0.0224022), correlation (0.549667)*/,
6, -9, 11, -13 /*mean (0.029161), correlation (0.546295)*/,
3, -1, 7, 12 /*mean (0.0303081), correlation (0.548599)*/,
11, -1, 12, 4 /*mean (0.0355151), correlation (0.523943)*/,
-3, 0, -3, 6 /*mean (0.0417904), correlation (0.543395)*/,
4, -11, 4, 12 /*mean (0.0487292), correlation (0.542818)*/,
2, -4, 2, 1 /*mean (0.0575124), correlation (0.554888)*/,
-10, -6, -8, 1 /*mean (0.0594242), correlation (0.544026)*/,
-13, 7, -11, 1 /*mean (0.0597391), correlation (0.550524)*/,
-13, 12, -11, -13 /*mean (0.0608974), correlation (0.55383)*/,
6, 0, 11, -13 /*mean (0.065126), correlation (0.552006)*/,
0, -1, 1, 4 /*mean (0.074224), correlation (0.546372)*/,
-13, 3, -9, -2 /*mean (0.0808592), correlation (0.554875)*/,
-9, 8, -6, -3 /*mean (0.0883378), correlation (0.551178)*/,
-13, -6, -8, -2 /*mean (0.0901035), correlation (0.548446)*/,
5, -9, 8, 10 /*mean (0.0949843), correlation (0.554694)*/,
2, 7, 3, -9 /*mean (0.0994152), correlation (0.550979)*/,
-1, -6, -1, -1 /*mean (0.10045), correlation (0.552714)*/,
9, 5, 11, -2 /*mean (0.100686), correlation (0.552594)*/,
11, -3, 12, -8 /*mean (0.101091), correlation (0.532394)*/,
3, 0, 3, 5 /*mean (0.101147), correlation (0.525576)*/,
-1, 4, 0, 10 /*mean (0.105263), correlation (0.531498)*/,
3, -6, 4, 5 /*mean (0.110785), correlation (0.540491)*/,
-13, 0, -10, 5 /*mean (0.112798), correlation (0.536582)*/,
5, 8, 12, 11 /*mean (0.114181), correlation (0.555793)*/,
8, 9, 9, -6 /*mean (0.117431), correlation (0.553763)*/,
7, -4, 8, -12 /*mean (0.118522), correlation (0.553452)*/,
-10, 4, -10, 9 /*mean (0.12094), correlation (0.554785)*/,
7, 3, 12, 4 /*mean (0.122582), correlation (0.555825)*/,
9, -7, 10, -2 /*mean (0.124978), correlation (0.549846)*/,
7, 0, 12, -2 /*mean (0.127002), correlation (0.537452)*/,
-1, -6, 0, -11 /*mean (0.127148), correlation (0.547401)*/
};
// compute the descriptor
void ComputeORB(const cv::Mat &img, vector<cv::KeyPoint> &keypoints, vector<DescType> &descriptors)
{
const int half_patch_size = 8;
const int half_boundary = 16;
int bad_points = 0;
for (auto &kp : keypoints)
{
if (kp.pt.x < half_boundary || kp.pt.y < half_boundary ||
kp.pt.x >= img.cols - half_boundary || kp.pt.y > img.rows - half_boundary)
{
// outside
bad_points++;
descriptors.push_back({});
continue;
}
float m01 = 0, m10 = 0;
for (int dx = -half_patch_size; dx < half_patch_size; ++dx)
{
for (int dy = -half_patch_size; dy < half_patch_size; ++dy)
{
uchar pixel = img.at<uchar>(kp.pt.y + dy, kp.pt.x + dx);
m01 += dx * pixel;
m10 += dy * pixel;
}
}
// angle should be arc tan(m01/m10)
float m_sqrt = sqrt(m01 * m01 + m10 * m10) + 1e-18; // avoid divid by zero
float sin_theta = m01 / m_sqrt;
float cos_theta = m10 / m_sqrt;
// compute the angle of this point
DescType desc(8, 0);
for (int i = 0; i < 8; i++)
{
uint32_t d = 0;
for (int k = 0; k < 32; k++)
{
int idx_pq = i * 8 + k;
cv::Point2f p(ORB_pattern[idx_pq * 4], ORB_pattern[idx_pq * 4 + 1]);
cv::Point2f q(ORB_pattern[idx_pq * 4 + 2], ORB_pattern[idx_pq * 4 + 3]);
// rotate with theta
cv::Point2f pp = cv::Point2f(cos_theta * p.x - sin_theta * p.y, sin_theta * p.x + cos_theta * p.y) + kp.pt;
cv::Point2f qq = cv::Point2f(cos_theta * q.x - sin_theta * q.y, sin_theta * q.x + cos_theta * q.y) + kp.pt;
if (img.at<uchar>(pp.y, pp.x) < img.at<uchar>(qq.y, qq.x))
{
d |= 1 << k;
}
}
desc[i] = d;
}
descriptors.push_back(desc);
}
cout << "bad/total: " << bad_points << "/" << keypoints.size() << endl;
}
void BfMatch(const vector<DescType> &desc1, const vector<DescType> &desc2, vector<cv::DMatch> &matches)
{
const int d_max = 40;
for (size_t i1 = 0; i1 < desc1.size(); ++i1)
{
if (desc1[i1].empty())
continue;
cv::DMatch m{i1, 0, 256};
for (size_t i2 = 0; i2 < desc2.size(); ++i2)
{
if (desc2[i2].empty())
continue;
int distance = 0;
for (int k = 0; k < 8; k++)
{
distance += _mm_popcnt_u32(desc1[i1][k] ^ desc2[i2][k]);
}
if (distance < d_max && distance < m.distance)
{
m.distance = distance;
m.trainIdx = i2;
}
}
if (m.distance < d_max)
{
matches.push_back(m);
}
}
}
