videostab::estimateGlobalMotionLeastSquares() doesn't work properly

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Hi there,

Could any one give me an example of using videostab APIs in OpenCV-3.3.0 to estimate global motion between two adjacent frames? I couldn't find any of them, so I have figured out my way (as explained step by step bellowed). I am trying with estimateGlobalMotionLeastSquares(), but things seem doesn't work well.

Here are 2 original gray frames (left: previous, right: current) between those I want to find the global motion matrix.

After the extraction of keypoints (using cv::goodFeatureTotrack).

Getting transformation matrix with estimateGlobalMotionLeastSquares(), then have it transform the previous frame into coordinate space of the current one (left) and compute difference image (right).

You can see that the result are terrible. In bellow I attach my piece of code, I would highly appreciate a help to figure out possible mistakes in it, or favorably a well working sample of code.

 //------------- READ 2 CONSECUTIVE FRAMES
 videoSrc.read(prev_frame);
 videoSrc.read(cur_frame);

 //------------- CONVERT TO GRAY SCALE & EXTRACT KEY POINTS
 cvtColor(prev_frame, prev_gray, COLOR_RGB2GRAY);
 cvtColor(cur_frame, cur_gray, COLOR_RGB2GRAY);

 goodFeaturesToTrack(prev_gray, prev_keypoints, 500, 0.04f, 10, cv::Mat(), 5, 0, 0.04f);
 goodFeaturesToTrack(cur_gray, cur_keypoints, 500, 0.04f, 10, cv::Mat(), 5, 0, 0.04f);


 //------------- ESTIMATE GLOBAL MOTION BASED ON THE ABOVE SETS OF KEY POINTS
 Mat m_transform = videostab::estimateGlobalMotionLeastSquares(prev_keypoints, cur_keypoints, videostab::MM_AFFINE, NULL);


 //------------- COMPUTE DIFFERENCE IMAGES
 Mat prev_gray_trans, diffImg, normImg;

 warpPerspective(prev_gray, prev_gray_trans, m_transform, Size(prev_gray.cols, prev_gray.rows));
 diffImg = cur_gray - prev_gray_trans;
 normalize (diffImg, normImg, 0, 255, NORM_MINMAX, CV_8UC1, Mat());