Automatic Image Stitching from video with opencv - c++

Question

Hy, i have error when i stitch frame from video,
here's my code
#include <stdio.h>
#include <iostream>
#include "opencv2/core/core.hpp"
#include "opencv2/features2d/features2d.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/nonfree/nonfree.hpp"
#include "opencv2/calib3d/calib3d.hpp"
#include "opencv2/imgproc/imgproc.hpp"
using namespace std;
using namespace cv;
Mat Stitching(Mat image1,Mat image2){
Mat gray_image1;
Mat gray_image2;
// Convert to Grayscale
cvtColor( image1, gray_image1, CV_RGB2GRAY );
cvtColor( image2, gray_image2, CV_RGB2GRAY );
//-- Step 1: Detect the keypoints using SURF Detector
int minHessian = 10;
SurfFeatureDetector detector( minHessian );
std::vector< KeyPoint > keypoints_object, keypoints_scene;
detector.detect( gray_image1, keypoints_object );
detector.detect( gray_image2, keypoints_scene );
//-- Step 2: Calculate descriptors (feature vectors)
SurfDescriptorExtractor extractor;
Mat descriptors_object, descriptors_scene;
extractor.compute( gray_image1, keypoints_object, descriptors_object );
extractor.compute( gray_image2, keypoints_scene, descriptors_scene );
//-- Step 3: Matching descriptor vectors using FLANN matcher
FlannBasedMatcher matcher;
std::vector< DMatch > matches;
matcher.match( descriptors_object, descriptors_scene, matches );
double max_dist = 0; double min_dist = 100;
//-- Quick calculation of max and min distances between keypoints
for( int i = 0; i < descriptors_object.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 );
//-- Use only "good" matches (i.e. whose distance is less than 3*min_dist )
std::vector< DMatch > good_matches;
for( int i = 0; i < descriptors_object.rows; i++ )
{ if( matches[i].distance < 3*min_dist )
{ good_matches.push_back( matches[i]); }
}
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( keypoints_object[ good_matches[i].queryIdx ].pt );
scene.push_back( keypoints_scene[ good_matches[i].trainIdx ].pt );
}
// Find the Homography Matrix
Mat H = findHomography( obj, scene, CV_RANSAC );
// Use the Homography Matrix to warp the images
cv::Mat result;
warpPerspective(image1,result,H,cv::Size(800,600));
cv::Mat half(result,cv::Rect(0,0,image2.cols,image2.rows));
image2.copyTo(half);
//imshow( "Result", result );
return result;
}
/** #function main */
int main( int argc, char** argv )
{
// Load the images
//Mat image1= imread( "E:\\Tugas Akhir\\image\\city2.jpg" );
//Mat image2= imread( "E:\\Tugas Akhir\\image\\city1.jpg" );
char *fileName = "E:\\Tugas Akhir\\Video Master\\indv_img_3a.avi";
/* Create a window */
cvNamedWindow("Stitching", CV_WINDOW_AUTOSIZE);
/* capture frame from video file */
CvCapture* capture = cvCreateFileCapture(fileName);
/* Create IplImage to point to each frame */
IplImage* frame;
IplImage before_frame;
Mat image1;
Mat image2;
cv::Mat result;
/* Loop until frame ended or ESC is pressed */
int loop=0;
//imshow( "Result", Stitching(image1,image2));
while(1) {
frame = cvQueryFrame(capture);
if(loop>0){
if(!frame) break;
image2=Mat(frame, false);
result=Stitching(image1,image2);
before_frame=result;
frame=&before_frame;
image1=result;
image2.release();
//imshow("Stitching",frame);
cvShowImage("Stitching",frame);
//break;
}else if(loop==0){
//Mat aimage1(frame);
image1=Mat(frame, false);
}
loop++;
char c = cvWaitKey(33);
if(c==27) break;
}
cvReleaseCapture(&capture);
/* delete window */
// cvDestroyWindow("Stitching");
// return EXIT_SUCCESS;
waitKey(0);
return 0;
}
if i load from image file, it works, image stitched, but when i try to stitch image from every video frame , it shows error
First-chance exception at 0x000007f886dd64a8 in matchingHomography.exe: Microsoft C++ exception: cv::Exception at memory location 0x0080e3b0..
Unhandled exception at 0x000007f886dd64a8 in matchingHomography.exe: Microsoft C++ exception: cv::Exception at memory location 0x0080e3b0..
line error
Mat H = findHomography( obj, scene, CV_RANSAC );
what's the error mean? and how to solve it
thanks

Answer 1

First off, you seem to be mixing C and C++ interfaces of OpenCV (OpenCV VideoCapture doc). For better readability stick to one of them (Since you are using C++ just stick to using C++ functions).
Since loading from image works, but Video doesn't, your video loading is probably the problem.
Try using cv::imshow("testWindow", frame) to show the frame loaded from video. Most likely there was no frame loaded.
One possible cause is that the video file is encoded in a format not supported by OpenCV. To check you can also run grab() and then retrieve(). The grab function will return if it was successful or not. Try grabbing a couple of frames, if all of them fail you probably don't have the necessary codec to decode this video.