Panoromic image construction

Question

I am trying to construct a panoromic view from different images. Initially I tried to stitch two images as part of panoromic construction. The two input images I am trying to stitch are:

I used ORB feature descriptor to find features in the image,then I found out Homography matrix between these two images. My code is:

int main(int argc, char **argv){

Mat img1 = imread(argv[1],1);
Mat img2 = imread(argv[2],1);
//-- Step 1: Detect the keypoints using orb Detector
std::vector<KeyPoint> kp2,kp1;

// Default parameters of ORB
int nfeatures=500;
float scaleFactor=1.2f;
int nlevels=8;
int edgeThreshold=15; // Changed default (31);
int firstLevel=0;
int WTA_K=2;
int scoreType=ORB::HARRIS_SCORE;
int patchSize=31;
int fastThreshold=20;

Ptr<ORB> detector = ORB::create(
        nfeatures,
        scaleFactor,
        nlevels,
        edgeThreshold,
        firstLevel,
        WTA_K,
        scoreType,
        patchSize,
        fastThreshold );
Mat descriptors_img1, descriptors_img2;


//-- Step 2: Calculate descriptors (feature vectors)
detector->detect(img1, kp1,descriptors_img1);
detector->detect(img2, kp2,descriptors_img2);


Ptr<DescriptorExtractor> extractor = ORB::create();
extractor->compute(img1, kp1, descriptors_img1 );
extractor->compute(img2, kp2, descriptors_img2 );
//-- Step 3: Matching descriptor vectors using FLANN matcher
if ( descriptors_img1.empty() )
    cvError(0,"MatchFinder","1st descriptor empty",__FILE__,__LINE__);
if ( descriptors_img2.empty() )
    cvError(0,"MatchFinder","2nd descriptor empty",__FILE__,__LINE__);
descriptors_img1.convertTo(descriptors_img1, CV_32F);
descriptors_img2.convertTo(descriptors_img2, CV_32F);
FlannBasedMatcher matcher;
std::vector<DMatch> matches;
matcher.match(descriptors_img1,descriptors_img2,matches);
double max_dist = 0; double min_dist = 100;

//-- Quick calculation of max and min distances between keypoints
for( int i = 0; i < descriptors_img1.rows; i++ )
{
    double dist = matches[i].distance;
    if( dist < min_dist )
        min_dist = dist;
    if( dist > max_dist )
        max_dist = dist;
}

printf("-- Max dist : %f \n", max_dist );
printf("-- Min dist : %f \n", min_dist );

//-- Draw only "good" matches (i.e. whose distance is less than 3*min_dist )
std::vector< DMatch > good_matches;

for( int i = 0; i < descriptors_img1.rows; i++ )
{
    if( matches[i].distance < 3*min_dist )
    {
        good_matches.push_back( matches[i]);
    }
}
Mat img_matches;
drawMatches(img1,kp1,img2,kp2,good_matches,img_matches,Scalar::all(-1),
        Scalar::all(-1),vector<char>(),DrawMatchesFlags::NOT_DRAW_SINGLE_POINTS );
std::vector<Point2f> obj;
std::vector<Point2f> scene;
for( int i = 0; i < good_matches.size(); i++ )
{
    //-- Get the keypoints from the good matches
    obj.push_back( kp1[ good_matches[i].queryIdx ].pt );
    scene.push_back( kp2[ good_matches[i].trainIdx ].pt );
}

Mat H = findHomography( obj, scene, CV_RANSAC );

After wards some people told me to include the following code

cv::Mat result;

warpPerspective( img1, result, H, cv::Size( img1.cols+img2.cols, img1.rows) );
cv::Mat half(result, cv::Rect(0, 0, img2.cols, img2.rows) );
img2.copyTo(half);
imshow("result",result);

The result I got is

I also tried using inbuilt opencv stitch function. And I got the result

I am trying to implement stitch function so I dont want to use inbuilt opencv stitch function. Can any one tell me where I went wrong and correct my code.Thanks in advance

Answer 1

Image stitching includes the following steps:

1. Feature finding
2. Find camera parameters
3. Warping
4. Exposure compensation
5. Seam Finding
6. Blending

You have to do all these steps in order to get the perfect result. In your code you have only done the first part, that is feature finding.

You can find a detailed explanation on how image stitching works in Learn OpenCV

Also I have the code on Github

Hope this helps.