opencv - Stitching more than 2 images - c++

Question

I am now trying to align more than two images together in C++ with opencv. The problem is when I stitch more than 2, the previous image cannot be loaded.
For example, imageContainer now contains three images.
First Image:
Second Image:
Third Image:
First iteration of the loop: (Combining the first and second image)
Second iteration of the loop: (Combining the result from first iteration and third image)
You can see that after the second iteration, the result image does not contain the object. (Left side of the last image is all black),
In main.cpp
cv::Mat result = *imageContainer.begin();
for(vector<cv::Mat>::iterator itr = imageContainer.begin(); itr != imageContainer.end(); itr++){
if(itr == imageContainer.begin())
continue;
result = applySURF(result, *itr);
}
In SURF.cpp
cv::Mat applySURF(cv::Mat object, cv::Mat image){
/* More codes here but it won't affect solving the problem */
cv::Mat result;
cv::warpPerspective(image, result, transformationMat, cv::Size(object.cols + image.cols, image.rows));
cv::Mat half(result, cv::Rect(0, 0, image.cols, image.rows));
object.copyTo(half);
imshow("Object", object);
imshow("Result", result);
cvWaitKey(0);
return result;
}
I guess the problem is related to Region Of Interest (ROI). How can I solve it?
Many Thanks.

Answer 1

Try the following code:)
I tested some cases and got a conclusion that if the size of target image is not same as the source image, it will reallocate a new Mat to be pasted. In your case the size of ROI is not same as object, it allocates a new Mat half and it is not related to result
anymore. So your copyTo function copies the object into the new Mat half instead of the ROI of result.
cv::Mat applySURF(cv::Mat object, cv::Mat image){
/* More codes here but it won't affect solving the problem */
cv::Mat result;
cv::warpPerspective(image, result, transformationMat, cv::Size(object.cols + image.cols, image.rows));
cv::Mat half(result, cv::Rect(0, 0, object.cols, object.rows));
object.copyTo(half);
cv::imshow("Object", object);
cv::imshow("Result", result);
cv::WaitKey(0);
return result;
}