?圖像拼接在實(shí)際的應(yīng)用場(chǎng)景很廣，比如無(wú)人機(jī)航拍，遙感圖像等等，圖像拼接是進(jìn)一步做圖像理解基礎(chǔ)步驟，拼接效果的好壞直接影響接下來(lái)的工作，所以一個(gè)好的圖像拼接算法非常重要。

再舉一個(gè)身邊的例子吧，你用你的手機(jī)對(duì)某一場(chǎng)景拍照，但是你沒有辦法一次將所有你要拍的景物全部拍下來(lái)，所以你對(duì)該場(chǎng)景從左往右依次拍了好幾張圖，來(lái)把你要拍的所有景物記錄下來(lái)。那么我們能不能把這些圖像拼接成一個(gè)大圖呢？我們利用opencv就可以做到圖像拼接的效果！

比如我們有對(duì)這兩張圖進(jìn)行拼接。

從上面兩張圖可以看出，這兩張圖有比較多的重疊部分，這也是拼接的基本要求。

那么要實(shí)現(xiàn)圖像拼接需要那幾步呢？簡(jiǎn)單來(lái)說有以下幾步：

對(duì)每幅圖進(jìn)行特征點(diǎn)提取

對(duì)對(duì)特征點(diǎn)進(jìn)行匹配

進(jìn)行圖像配準(zhǔn)

把圖像拷貝到另一幅圖像的特定位置

對(duì)重疊邊界進(jìn)行特殊處理

好吧，那就開始正式實(shí)現(xiàn)圖像配準(zhǔn)。

第一步就是特征點(diǎn)提取?，F(xiàn)在CV領(lǐng)域有很多特征點(diǎn)的定義，比如sift、surf、harris角點(diǎn)、ORB都是很有名的特征因子，都可以用來(lái)做圖像拼接的工作，他們各有優(yōu)勢(shì)。本文將使用ORB和SURF進(jìn)行圖像拼接，用其他方法進(jìn)行拼接也是類似的。

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基于SURF的圖像拼接

用SIFT算法來(lái)實(shí)現(xiàn)圖像拼接是很常用的方法，但是因?yàn)镾IFT計(jì)算量很大，所以在速度要求很高的場(chǎng)合下不再適用。所以，它的改進(jìn)方法SURF因?yàn)樵谒俣确矫嬗辛嗣黠@的提高（速度是SIFT的3倍），所以在圖像拼接領(lǐng)域還是大有作為。雖說SURF精確度和穩(wěn)定性不及SIFT，但是其綜合能力還是優(yōu)越一些。下面將詳細(xì)介紹拼接的主要步驟。

1.特征點(diǎn)提取和匹配

特征點(diǎn)提取和匹配的方法我在上一篇文章《OpenCV探索之路（二十三）：特征檢測(cè)和特征匹配方法匯總》中做了詳細(xì)的介紹，在這里直接使用上文所總結(jié)的SURF特征提取和特征匹配的方法。

//提取特征點(diǎn) SurfFeatureDetector Detector(2000); vector<KeyPoint> keyPoint1, keyPoint2; Detector.detect(image1, keyPoint1); Detector.detect(image2, keyPoint2);//特征點(diǎn)描述，為下邊的特征點(diǎn)匹配做準(zhǔn)備 SurfDescriptorExtractor Descriptor; Mat imageDesc1, imageDesc2; Descriptor.compute(image1, keyPoint1, imageDesc1); Descriptor.compute(image2, keyPoint2, imageDesc2);FlannBasedMatcher matcher; vector<vector<DMatch> > matchePoints; vector<DMatch> GoodMatchePoints;vector<Mat> train_desc(1, imageDesc1); matcher.add(train_desc); matcher.train();matcher.knnMatch(imageDesc2, matchePoints, 2); cout << "total match points: " << matchePoints.size() << endl;// Lowe's algorithm,獲取優(yōu)秀匹配點(diǎn) for (int i = 0; i < matchePoints.size(); i++) {if (matchePoints[i][0].distance < 0.4 * matchePoints[i][1].distance){GoodMatchePoints.push_back(matchePoints[i][0]);} }Mat first_match; drawMatches(image02, keyPoint2, image01, keyPoint1, GoodMatchePoints, first_match); imshow("first_match ", first_match);

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2.圖像配準(zhǔn)

這樣子我們就可以得到了兩幅待拼接圖的匹配點(diǎn)集，接下來(lái)我們進(jìn)行圖像的配準(zhǔn)，即將兩張圖像轉(zhuǎn)換為同一坐標(biāo)下，這里我們需要使用findHomography函數(shù)來(lái)求得變換矩陣。但是需要注意的是，findHomography函數(shù)所要用到的點(diǎn)集是Point2f類型的，所有我們需要對(duì)我們剛得到的點(diǎn)集GoodMatchePoints再做一次處理，使其轉(zhuǎn)換為Point2f類型的點(diǎn)集。

vector<Point2f> imagePoints1, imagePoints2;for (int i = 0; i<GoodMatchePoints.size(); i++) {imagePoints2.push_back(keyPoint2[GoodMatchePoints[i].queryIdx].pt);imagePoints1.push_back(keyPoint1[GoodMatchePoints[i].trainIdx].pt); }

這樣子，我們就可以拿著imagePoints1, imagePoints2去求變換矩陣了，并且實(shí)現(xiàn)圖像配準(zhǔn)。值得注意的是findHomography函數(shù)的參數(shù)中我們選澤了CV_RANSAC，這表明我們選擇RANSAC算法繼續(xù)篩選可靠地匹配點(diǎn)，這使得匹配點(diǎn)解更為精確。

//獲取圖像1到圖像2的投影映射矩陣 尺寸為3*3 Mat homo = findHomography(imagePoints1, imagePoints2, CV_RANSAC); 也可以使用getPerspectiveTransform方法獲得透視變換矩陣，不過要求只能有4個(gè)點(diǎn)，效果稍差 //Mat homo=getPerspectiveTransform(imagePoints1,imagePoints2); cout << "變換矩陣為：\n" << homo << endl << endl; //輸出映射矩陣 //圖像配準(zhǔn) Mat imageTransform1, imageTransform2; warpPerspective(image01, imageTransform1, homo, Size(MAX(corners.right_top.x, corners.right_bottom.x), image02.rows)); //warpPerspective(image01, imageTransform2, adjustMat*homo, Size(image02.cols*1.3, image02.rows*1.8)); imshow("直接經(jīng)過透視矩陣變換", imageTransform1); imwrite("trans1.jpg", imageTransform1);

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3. 圖像拷貝

拷貝的思路很簡(jiǎn)單，就是將左圖直接拷貝到配準(zhǔn)圖上就可以了。

//創(chuàng)建拼接后的圖,需提前計(jì)算圖的大小 int dst_width = imageTransform1.cols; //取最右點(diǎn)的長(zhǎng)度為拼接圖的長(zhǎng)度 int dst_height = image02.rows;Mat dst(dst_height, dst_width, CV_8UC3); dst.setTo(0);imageTransform1.copyTo(dst(Rect(0, 0, imageTransform1.cols, imageTransform1.rows))); image02.copyTo(dst(Rect(0, 0, image02.cols, image02.rows)));imshow("b_dst", dst);

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4.圖像融合（去裂縫處理）

從上圖可以看出，兩圖的拼接并不自然，原因就在于拼接圖的交界處，兩圖因?yàn)楣庹丈珴傻脑蚴沟脙蓤D交界處的過渡很糟糕，所以需要特定的處理解決這種不自然。這里的處理思路是加權(quán)融合，在重疊部分由前一幅圖像慢慢過渡到第二幅圖像，即將圖像的重疊區(qū)域的像素值按一定的權(quán)值相加合成新的圖像。

//優(yōu)化兩圖的連接處，使得拼接自然 void OptimizeSeam(Mat& img1, Mat& trans, Mat& dst) {int start = MIN(corners.left_top.x, corners.left_bottom.x);//開始位置，即重疊區(qū)域的左邊界 double processWidth = img1.cols - start;//重疊區(qū)域的寬度 int rows = dst.rows;int cols = img1.cols; //注意，是列數(shù)*通道數(shù)double alpha = 1;//img1中像素的權(quán)重 for (int i = 0; i < rows; i++){uchar* p = img1.ptr<uchar>(i); //獲取第i行的首地址uchar* t = trans.ptr<uchar>(i);uchar* d = dst.ptr<uchar>(i);for (int j = start; j < cols; j++){//如果遇到圖像trans中無(wú)像素的黑點(diǎn)，則完全拷貝img1中的數(shù)據(jù)if (t[j * 3] == 0 && t[j * 3 + 1] == 0 && t[j * 3 + 2] == 0){alpha = 1;}else{//img1中像素的權(quán)重，與當(dāng)前處理點(diǎn)距重疊區(qū)域左邊界的距離成正比，實(shí)驗(yàn)證明，這種方法確實(shí)好 alpha = (processWidth - (j - start)) / processWidth;}d[j * 3] = p[j * 3] * alpha + t[j * 3] * (1 - alpha);d[j * 3 + 1] = p[j * 3 + 1] * alpha + t[j * 3 + 1] * (1 - alpha);d[j * 3 + 2] = p[j * 3 + 2] * alpha + t[j * 3 + 2] * (1 - alpha);}}}

多嘗試幾張，驗(yàn)證拼接效果

測(cè)試一

測(cè)試二

測(cè)試三

最后給出完整的SURF算法實(shí)現(xiàn)的拼接代碼。

#include "highgui/highgui.hpp" #include "opencv2/nonfree/nonfree.hpp" #include "opencv2/legacy/legacy.hpp" #include <iostream> using namespace cv; using namespace std;void OptimizeSeam(Mat& img1, Mat& trans, Mat& dst);typedef struct {Point2f left_top;Point2f left_bottom;Point2f right_top;Point2f right_bottom; }four_corners_t;four_corners_t corners;void CalcCorners(const Mat& H, const Mat& src) {double v2[] = { 0, 0, 1 };//左上角double v1[3];//變換后的坐標(biāo)值Mat V2 = Mat(3, 1, CV_64FC1, v2); //列向量Mat V1 = Mat(3, 1, CV_64FC1, v1); //列向量V1 = H * V2;//左上角(0,0,1)cout << "V2: " << V2 << endl;cout << "V1: " << V1 << endl;corners.left_top.x = v1[0] / v1[2];corners.left_top.y = v1[1] / v1[2];//左下角(0,src.rows,1)v2[0] = 0;v2[1] = src.rows;v2[2] = 1;V2 = Mat(3, 1, CV_64FC1, v2); //列向量V1 = Mat(3, 1, CV_64FC1, v1); //列向量V1 = H * V2;corners.left_bottom.x = v1[0] / v1[2];corners.left_bottom.y = v1[1] / v1[2];//右上角(src.cols,0,1)v2[0] = src.cols;v2[1] = 0;v2[2] = 1;V2 = Mat(3, 1, CV_64FC1, v2); //列向量V1 = Mat(3, 1, CV_64FC1, v1); //列向量V1 = H * V2;corners.right_top.x = v1[0] / v1[2];corners.right_top.y = v1[1] / v1[2];//右下角(src.cols,src.rows,1)v2[0] = src.cols;v2[1] = src.rows;v2[2] = 1;V2 = Mat(3, 1, CV_64FC1, v2); //列向量V1 = Mat(3, 1, CV_64FC1, v1); //列向量V1 = H * V2;corners.right_bottom.x = v1[0] / v1[2];corners.right_bottom.y = v1[1] / v1[2];}int main(int argc, char *argv[]) {Mat image01 = imread("g5.jpg", 1); //右圖Mat image02 = imread("g4.jpg", 1); //左圖imshow("p2", image01);imshow("p1", image02);//灰度圖轉(zhuǎn)換 Mat image1, image2;cvtColor(image01, image1, CV_RGB2GRAY);cvtColor(image02, image2, CV_RGB2GRAY);//提取特征點(diǎn) SurfFeatureDetector Detector(2000); vector<KeyPoint> keyPoint1, keyPoint2;Detector.detect(image1, keyPoint1);Detector.detect(image2, keyPoint2);//特征點(diǎn)描述，為下邊的特征點(diǎn)匹配做準(zhǔn)備 SurfDescriptorExtractor Descriptor;Mat imageDesc1, imageDesc2;Descriptor.compute(image1, keyPoint1, imageDesc1);Descriptor.compute(image2, keyPoint2, imageDesc2);FlannBasedMatcher matcher;vector<vector<DMatch> > matchePoints;vector<DMatch> GoodMatchePoints;vector<Mat> train_desc(1, imageDesc1);matcher.add(train_desc);matcher.train();matcher.knnMatch(imageDesc2, matchePoints, 2);cout << "total match points: " << matchePoints.size() << endl;// Lowe's algorithm,獲取優(yōu)秀匹配點(diǎn)for (int i = 0; i < matchePoints.size(); i++){if (matchePoints[i][0].distance < 0.4 * matchePoints[i][1].distance){GoodMatchePoints.push_back(matchePoints[i][0]);}}Mat first_match;drawMatches(image02, keyPoint2, image01, keyPoint1, GoodMatchePoints, first_match);imshow("first_match ", first_match);vector<Point2f> imagePoints1, imagePoints2;for (int i = 0; i<GoodMatchePoints.size(); i++){imagePoints2.push_back(keyPoint2[GoodMatchePoints[i].queryIdx].pt);imagePoints1.push_back(keyPoint1[GoodMatchePoints[i].trainIdx].pt);}//獲取圖像1到圖像2的投影映射矩陣 尺寸為3*3 Mat homo = findHomography(imagePoints1, imagePoints2, CV_RANSAC);也可以使用getPerspectiveTransform方法獲得透視變換矩陣，不過要求只能有4個(gè)點(diǎn)，效果稍差 //Mat homo=getPerspectiveTransform(imagePoints1,imagePoints2); cout << "變換矩陣為：\n" << homo << endl << endl; //輸出映射矩陣 //計(jì)算配準(zhǔn)圖的四個(gè)頂點(diǎn)坐標(biāo)CalcCorners(homo, image01);cout << "left_top:" << corners.left_top << endl;cout << "left_bottom:" << corners.left_bottom << endl;cout << "right_top:" << corners.right_top << endl;cout << "right_bottom:" << corners.right_bottom << endl;//圖像配準(zhǔn) Mat imageTransform1, imageTransform2;warpPerspective(image01, imageTransform1, homo, Size(MAX(corners.right_top.x, corners.right_bottom.x), image02.rows));//warpPerspective(image01, imageTransform2, adjustMat*homo, Size(image02.cols*1.3, image02.rows*1.8));imshow("直接經(jīng)過透視矩陣變換", imageTransform1);imwrite("trans1.jpg", imageTransform1);//創(chuàng)建拼接后的圖,需提前計(jì)算圖的大小int dst_width = imageTransform1.cols; //取最右點(diǎn)的長(zhǎng)度為拼接圖的長(zhǎng)度int dst_height = image02.rows;Mat dst(dst_height, dst_width, CV_8UC3);dst.setTo(0);imageTransform1.copyTo(dst(Rect(0, 0, imageTransform1.cols, imageTransform1.rows)));image02.copyTo(dst(Rect(0, 0, image02.cols, image02.rows)));imshow("b_dst", dst);OptimizeSeam(image02, imageTransform1, dst);imshow("dst", dst);imwrite("dst.jpg", dst);waitKey();return 0; }//優(yōu)化兩圖的連接處，使得拼接自然 void OptimizeSeam(Mat& img1, Mat& trans, Mat& dst) {int start = MIN(corners.left_top.x, corners.left_bottom.x);//開始位置，即重疊區(qū)域的左邊界 double processWidth = img1.cols - start;//重疊區(qū)域的寬度 int rows = dst.rows;int cols = img1.cols; //注意，是列數(shù)*通道數(shù)double alpha = 1;//img1中像素的權(quán)重 for (int i = 0; i < rows; i++){uchar* p = img1.ptr<uchar>(i); //獲取第i行的首地址uchar* t = trans.ptr<uchar>(i);uchar* d = dst.ptr<uchar>(i);for (int j = start; j < cols; j++){//如果遇到圖像trans中無(wú)像素的黑點(diǎn)，則完全拷貝img1中的數(shù)據(jù)if (t[j * 3] == 0 && t[j * 3 + 1] == 0 && t[j * 3 + 2] == 0){alpha = 1;}else{//img1中像素的權(quán)重，與當(dāng)前處理點(diǎn)距重疊區(qū)域左邊界的距離成正比，實(shí)驗(yàn)證明，這種方法確實(shí)好 alpha = (processWidth - (j - start)) / processWidth;}d[j * 3] = p[j * 3] * alpha + t[j * 3] * (1 - alpha);d[j * 3 + 1] = p[j * 3 + 1] * alpha + t[j * 3 + 1] * (1 - alpha);d[j * 3 + 2] = p[j * 3 + 2] * alpha + t[j * 3 + 2] * (1 - alpha);}}}

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基于ORB的圖像拼接

利用ORB進(jìn)行圖像拼接的思路跟上面的思路基本一樣，只是特征提取和特征點(diǎn)匹配的方式略有差異罷了。這里就不再詳細(xì)介紹思路了，直接貼代碼看效果。

#include "highgui/highgui.hpp" #include "opencv2/nonfree/nonfree.hpp" #include "opencv2/legacy/legacy.hpp" #include <iostream> using namespace cv; using namespace std;void OptimizeSeam(Mat& img1, Mat& trans, Mat& dst);typedef struct {Point2f left_top;Point2f left_bottom;Point2f right_top;Point2f right_bottom; }four_corners_t;four_corners_t corners;void CalcCorners(const Mat& H, const Mat& src) {double v2[] = { 0, 0, 1 };//左上角double v1[3];//變換后的坐標(biāo)值Mat V2 = Mat(3, 1, CV_64FC1, v2); //列向量Mat V1 = Mat(3, 1, CV_64FC1, v1); //列向量V1 = H * V2;//左上角(0,0,1)cout << "V2: " << V2 << endl;cout << "V1: " << V1 << endl;corners.left_top.x = v1[0] / v1[2];corners.left_top.y = v1[1] / v1[2];//左下角(0,src.rows,1)v2[0] = 0;v2[1] = src.rows;v2[2] = 1;V2 = Mat(3, 1, CV_64FC1, v2); //列向量V1 = Mat(3, 1, CV_64FC1, v1); //列向量V1 = H * V2;corners.left_bottom.x = v1[0] / v1[2];corners.left_bottom.y = v1[1] / v1[2];//右上角(src.cols,0,1)v2[0] = src.cols;v2[1] = 0;v2[2] = 1;V2 = Mat(3, 1, CV_64FC1, v2); //列向量V1 = Mat(3, 1, CV_64FC1, v1); //列向量V1 = H * V2;corners.right_top.x = v1[0] / v1[2];corners.right_top.y = v1[1] / v1[2];//右下角(src.cols,src.rows,1)v2[0] = src.cols;v2[1] = src.rows;v2[2] = 1;V2 = Mat(3, 1, CV_64FC1, v2); //列向量V1 = Mat(3, 1, CV_64FC1, v1); //列向量V1 = H * V2;corners.right_bottom.x = v1[0] / v1[2];corners.right_bottom.y = v1[1] / v1[2];}int main(int argc, char *argv[]) {Mat image01 = imread("t1.jpg", 1); //右圖Mat image02 = imread("t2.jpg", 1); //左圖imshow("p2", image01);imshow("p1", image02);//灰度圖轉(zhuǎn)換 Mat image1, image2;cvtColor(image01, image1, CV_RGB2GRAY);cvtColor(image02, image2, CV_RGB2GRAY);//提取特征點(diǎn) OrbFeatureDetector surfDetector(3000); vector<KeyPoint> keyPoint1, keyPoint2;surfDetector.detect(image1, keyPoint1);surfDetector.detect(image2, keyPoint2);//特征點(diǎn)描述，為下邊的特征點(diǎn)匹配做準(zhǔn)備 OrbDescriptorExtractor SurfDescriptor;Mat imageDesc1, imageDesc2;SurfDescriptor.compute(image1, keyPoint1, imageDesc1);SurfDescriptor.compute(image2, keyPoint2, imageDesc2);flann::Index flannIndex(imageDesc1, flann::LshIndexParams(12, 20, 2), cvflann::FLANN_DIST_HAMMING);vector<DMatch> GoodMatchePoints;Mat macthIndex(imageDesc2.rows, 2, CV_32SC1), matchDistance(imageDesc2.rows, 2, CV_32FC1);flannIndex.knnSearch(imageDesc2, macthIndex, matchDistance, 2, flann::SearchParams());// Lowe's algorithm,獲取優(yōu)秀匹配點(diǎn)for (int i = 0; i < matchDistance.rows; i++){if (matchDistance.at<float>(i, 0) < 0.4 * matchDistance.at<float>(i, 1)){DMatch dmatches(i, macthIndex.at<int>(i, 0), matchDistance.at<float>(i, 0));GoodMatchePoints.push_back(dmatches);}}Mat first_match;drawMatches(image02, keyPoint2, image01, keyPoint1, GoodMatchePoints, first_match);imshow("first_match ", first_match);vector<Point2f> imagePoints1, imagePoints2;for (int i = 0; i<GoodMatchePoints.size(); i++){imagePoints2.push_back(keyPoint2[GoodMatchePoints[i].queryIdx].pt);imagePoints1.push_back(keyPoint1[GoodMatchePoints[i].trainIdx].pt);}//獲取圖像1到圖像2的投影映射矩陣 尺寸為3*3 Mat homo = findHomography(imagePoints1, imagePoints2, CV_RANSAC);也可以使用getPerspectiveTransform方法獲得透視變換矩陣，不過要求只能有4個(gè)點(diǎn)，效果稍差 //Mat homo=getPerspectiveTransform(imagePoints1,imagePoints2); cout << "變換矩陣為：\n" << homo << endl << endl; //輸出映射矩陣 //計(jì)算配準(zhǔn)圖的四個(gè)頂點(diǎn)坐標(biāo)CalcCorners(homo, image01);cout << "left_top:" << corners.left_top << endl;cout << "left_bottom:" << corners.left_bottom << endl;cout << "right_top:" << corners.right_top << endl;cout << "right_bottom:" << corners.right_bottom << endl;//圖像配準(zhǔn) Mat imageTransform1, imageTransform2;warpPerspective(image01, imageTransform1, homo, Size(MAX(corners.right_top.x, corners.right_bottom.x), image02.rows));//warpPerspective(image01, imageTransform2, adjustMat*homo, Size(image02.cols*1.3, image02.rows*1.8));imshow("直接經(jīng)過透視矩陣變換", imageTransform1);imwrite("trans1.jpg", imageTransform1);//創(chuàng)建拼接后的圖,需提前計(jì)算圖的大小int dst_width = imageTransform1.cols; //取最右點(diǎn)的長(zhǎng)度為拼接圖的長(zhǎng)度int dst_height = image02.rows;Mat dst(dst_height, dst_width, CV_8UC3);dst.setTo(0);imageTransform1.copyTo(dst(Rect(0, 0, imageTransform1.cols, imageTransform1.rows)));image02.copyTo(dst(Rect(0, 0, image02.cols, image02.rows)));imshow("b_dst", dst);OptimizeSeam(image02, imageTransform1, dst);imshow("dst", dst);imwrite("dst.jpg", dst);waitKey();return 0; }//優(yōu)化兩圖的連接處，使得拼接自然 void OptimizeSeam(Mat& img1, Mat& trans, Mat& dst) {int start = MIN(corners.left_top.x, corners.left_bottom.x);//開始位置，即重疊區(qū)域的左邊界 double processWidth = img1.cols - start;//重疊區(qū)域的寬度 int rows = dst.rows;int cols = img1.cols; //注意，是列數(shù)*通道數(shù)double alpha = 1;//img1中像素的權(quán)重 for (int i = 0; i < rows; i++){uchar* p = img1.ptr<uchar>(i); //獲取第i行的首地址uchar* t = trans.ptr<uchar>(i);uchar* d = dst.ptr<uchar>(i);for (int j = start; j < cols; j++){//如果遇到圖像trans中無(wú)像素的黑點(diǎn)，則完全拷貝img1中的數(shù)據(jù)if (t[j * 3] == 0 && t[j * 3 + 1] == 0 && t[j * 3 + 2] == 0){alpha = 1;}else{//img1中像素的權(quán)重，與當(dāng)前處理點(diǎn)距重疊區(qū)域左邊界的距離成正比，實(shí)驗(yàn)證明，這種方法確實(shí)好 alpha = (processWidth - (j - start)) / processWidth;}d[j * 3] = p[j * 3] * alpha + t[j * 3] * (1 - alpha);d[j * 3 + 1] = p[j * 3 + 1] * alpha + t[j * 3 + 1] * (1 - alpha);d[j * 3 + 2] = p[j * 3 + 2] * alpha + t[j * 3 + 2] * (1 - alpha);}}}

看一看拼接效果，我覺得還是不錯(cuò)的。

看一下這一組圖片，這組圖片產(chǎn)生了鬼影，為什么？因?yàn)閮煞鶊D中的人物走動(dòng)了啊！所以要做圖像拼接，盡量保證使用的是靜態(tài)圖片，不要加入一些動(dòng)態(tài)因素干擾拼接。

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opencv自帶的拼接算法stitch

opencv其實(shí)自己就有實(shí)現(xiàn)圖像拼接的算法，當(dāng)然效果也是相當(dāng)好的，但是因?yàn)槠鋵?shí)現(xiàn)很復(fù)雜，而且代碼量很龐大，其實(shí)在一些小應(yīng)用下的拼接有點(diǎn)殺雞用牛刀的感覺。最近在閱讀sticth源碼時(shí)，發(fā)現(xiàn)其中有幾個(gè)很有意思的地方。

1.opencv stitch選擇的特征檢測(cè)方式

一直很好奇opencv stitch算法到底選用了哪個(gè)算法作為其特征檢測(cè)方式，是ORB，SIFT還是SURF？讀源碼終于看到答案。

#ifdef HAVE_OPENCV_NONFREEstitcher.setFeaturesFinder(new detail::SurfFeaturesFinder()); #elsestitcher.setFeaturesFinder(new detail::OrbFeaturesFinder()); #endif

在源碼createDefault函數(shù)中（默認(rèn)設(shè)置），第一選擇是SURF,第二選擇才是ORB（沒有NONFREE模塊才選），所以既然大牛們這么選擇，必然是經(jīng)過綜合考慮的，所以應(yīng)該SURF算法在圖像拼接有著更優(yōu)秀的效果。

2.opencv stitch獲取匹配點(diǎn)的方式

以下代碼是opencv stitch源碼中的特征點(diǎn)提取部分，作者使用了兩次特征點(diǎn)提取的思路：先對(duì)圖一進(jìn)行特征點(diǎn)提取和篩選匹配（1->2），再對(duì)圖二進(jìn)行特征點(diǎn)的提取和匹配（2->1），這跟我們平時(shí)的一次提取的思路不同，這種二次提取的思路可以保證更多的匹配點(diǎn)被選中，匹配點(diǎn)越多，findHomography求出的變換越準(zhǔn)確。這個(gè)思路值得借鑒。

matches_info.matches.clear();Ptr<flann::IndexParams> indexParams = new flann::KDTreeIndexParams(); Ptr<flann::SearchParams> searchParams = new flann::SearchParams();if (features2.descriptors.depth() == CV_8U) {indexParams->setAlgorithm(cvflann::FLANN_INDEX_LSH);searchParams->setAlgorithm(cvflann::FLANN_INDEX_LSH); }FlannBasedMatcher matcher(indexParams, searchParams); vector< vector<DMatch> > pair_matches; MatchesSet matches;// Find 1->2 matches matcher.knnMatch(features1.descriptors, features2.descriptors, pair_matches, 2); for (size_t i = 0; i < pair_matches.size(); ++i) {if (pair_matches[i].size() < 2)continue;const DMatch& m0 = pair_matches[i][0];const DMatch& m1 = pair_matches[i][1];if (m0.distance < (1.f - match_conf_) * m1.distance){matches_info.matches.push_back(m0);matches.insert(make_pair(m0.queryIdx, m0.trainIdx));} } LOG("\n1->2 matches: " << matches_info.matches.size() << endl);// Find 2->1 matches pair_matches.clear(); matcher.knnMatch(features2.descriptors, features1.descriptors, pair_matches, 2); for (size_t i = 0; i < pair_matches.size(); ++i) {if (pair_matches[i].size() < 2)continue;const DMatch& m0 = pair_matches[i][0];const DMatch& m1 = pair_matches[i][1];if (m0.distance < (1.f - match_conf_) * m1.distance)if (matches.find(make_pair(m0.trainIdx, m0.queryIdx)) == matches.end())matches_info.matches.push_back(DMatch(m0.trainIdx, m0.queryIdx, m0.distance)); } LOG("1->2 & 2->1 matches: " << matches_info.matches.size() << endl);

這里我仿照opencv源碼二次提取特征點(diǎn)的思路對(duì)我原有拼接代碼進(jìn)行改寫，實(shí)驗(yàn)證明獲取的匹配點(diǎn)確實(shí)較一次提取要多。

//提取特征點(diǎn) SiftFeatureDetector Detector(1000); // 海塞矩陣閾值，在這里調(diào)整精度，值越大點(diǎn)越少，越精準(zhǔn) vector<KeyPoint> keyPoint1, keyPoint2; Detector.detect(image1, keyPoint1); Detector.detect(image2, keyPoint2);//特征點(diǎn)描述，為下邊的特征點(diǎn)匹配做準(zhǔn)備 SiftDescriptorExtractor Descriptor; Mat imageDesc1, imageDesc2; Descriptor.compute(image1, keyPoint1, imageDesc1); Descriptor.compute(image2, keyPoint2, imageDesc2);FlannBasedMatcher matcher; vector<vector<DMatch> > matchePoints; vector<DMatch> GoodMatchePoints;MatchesSet matches;vector<Mat> train_desc(1, imageDesc1); matcher.add(train_desc); matcher.train();matcher.knnMatch(imageDesc2, matchePoints, 2);// Lowe's algorithm,獲取優(yōu)秀匹配點(diǎn) for (int i = 0; i < matchePoints.size(); i++) {if (matchePoints[i][0].distance < 0.4 * matchePoints[i][1].distance){GoodMatchePoints.push_back(matchePoints[i][0]);matches.insert(make_pair(matchePoints[i][0].queryIdx, matchePoints[i][0].trainIdx));} } cout<<"\n1->2 matches: " << GoodMatchePoints.size() << endl;#if 1FlannBasedMatcher matcher2; matchePoints.clear(); vector<Mat> train_desc2(1, imageDesc2); matcher2.add(train_desc2); matcher2.train();matcher2.knnMatch(imageDesc1, matchePoints, 2); // Lowe's algorithm,獲取優(yōu)秀匹配點(diǎn) for (int i = 0; i < matchePoints.size(); i++) {if (matchePoints[i][0].distance < 0.4 * matchePoints[i][1].distance){if (matches.find(make_pair(matchePoints[i][0].trainIdx, matchePoints[i][0].queryIdx)) == matches.end()){GoodMatchePoints.push_back(DMatch(matchePoints[i][0].trainIdx, matchePoints[i][0].queryIdx, matchePoints[i][0].distance));}} } cout<<"1->2 & 2->1 matches: " << GoodMatchePoints.size() << endl; #endif

最后再看一下opencv stitch的拼接效果吧~速度雖然比較慢，但是效果還是很好的。

#include <iostream> #include <opencv2/core/core.hpp> #include <opencv2/highgui/highgui.hpp> #include <opencv2/imgproc/imgproc.hpp> #include <opencv2/stitching/stitcher.hpp> using namespace std; using namespace cv; bool try_use_gpu = false; vector<Mat> imgs; string result_name = "dst1.jpg"; int main(int argc, char * argv[]) {Mat img1 = imread("34.jpg");Mat img2 = imread("35.jpg");imshow("p1", img1);imshow("p2", img2);if (img1.empty() || img2.empty()){cout << "Can't read image" << endl;return -1;}imgs.push_back(img1);imgs.push_back(img2);Stitcher stitcher = Stitcher::createDefault(try_use_gpu);// 使用stitch函數(shù)進(jìn)行拼接Mat pano;Stitcher::Status status = stitcher.stitch(imgs, pano);if (status != Stitcher::OK){cout << "Can't stitch images, error code = " << int(status) << endl;return -1;}imwrite(result_name, pano);Mat pano2 = pano.clone();// 顯示源圖像，和結(jié)果圖像imshow("全景圖像", pano);if (waitKey() == 27)return 0; }

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原文地址：https://www.cnblogs.com/skyfsm/p/7411961.html

感謝原作者。

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