Opencv image translation artifacts (C++) - c++

Question

I have created a stitching algorithm that can stitch many images together. It doesn't use a bundle adjustment but that is a later addition to be made.
After finding the homography between the two images I am stitching I do a series of translations, perspectiveTransforms and warpPerspectives to achieve my end result. The following two images are two image stitched the first being images passed left to right and the latter being images passed right to left. Each image includes information about the translation matrix created to stitch the images. The result image is the new padded size of a blank images that will contain the stitched images (what you are seeing pictured).
Image 1: Min x 478.711 Min y 3.16 Max x 1853.66 Max y 1449.42
Image 2: Min x 0 Min y 0 Max x 1200 Max y 900
Result Image: Min x 0 Min y 0 Max x 1853.66 Max y 1449.42
[1, 0, 0;
0, 1, 0; Stitch 2
0, 0, 1]
Image 1: Min x -671.462 Min y -461.816 Max x 652.656 Max y 655.324
Image 2: Min x 0 Min y 0 Max x 1200 Max y 900
Result Image: Min x -671.462 Min y -461.816 Max x 1200 Max y 900
[1, 0, 672;
0, 1, 462; Stitch2/Rev
0, 0, 1]
Looks like it works great which is awesome. However when I run the code piping in 3 images I get weird lines where the black background should be and then my padding begins to fail. Again reference images and translations.
---------------------
Image 1: Min x 390.279 Min y 72.4343 Max x 1658.93 Max y 1110.17
Image 2: Min x 0 Min y 0 Max x 1200 Max y 900
Result Image: Min x 0 Min y 0 Max x 1658.93 Max y 1110.17
[1, 0, 0;
0, 1, 0;
0, 0, 1]
Image 1: Min x 439.817 Min y -20.4711 Max x 2205.2 Max y 1288.93
Image 2: Min x 0 Min y 0 Max x 1200 Max y 900
Result Image: Min x 0 Min y -20.4711 Max x 2205.2 Max y 1288.93
[1, 0, 0;
0, 1, 21;
0, 0, 1]
---------------------
Code for this section follows. Any help is appreciated.
Mat result, descriptors_updated;
vector<Point2f> fourPointImage1, fourPointImage2, image1dst, image2dst;
vector<KeyPoint> keypoints_updated;
float min_x, min_y, max_x, max_y, result_x, result_y, img1_min_x, img1_min_y, img2_min_x, img2_min_y,img1_max_x, img1_max_y, img2_max_x, img2_max_y, result_min_x, result_max_x, result_min_y, result_max_y;
//get four corners of image MATs
fourPointImage1 = fourCorners(image1);
fourPointImage2 = fourCorners(image2);
//get the min and max corners
tie(min_x, min_y, max_x, max_y) = minMaxCorners(fourPointImage1);
//- Htr use to map image one to result in line with the already warped image two
Mat Htr = Mat::eye(3,3,CV_64F);
if (min_x < 0){
max_x = image2.size().width - min_x;
Htr.at<double>(0,2)= -min_x;
}
if (min_y < 0){
max_y = image2.size().height - min_y;
Htr.at<double>(1,2)= -min_y;
}
//- Need to create a padded blank image to accomodate stitched images.
//- Must first determine where the translations of the two images will end up to determine if shift is needed and how much to pad blank image
perspectiveTransform(fourPointImage1, image1dst, Htr*homography);
perspectiveTransform(fourPointImage2, image2dst, Htr);
//- Now determine what is out of bounds
//New coordinates for image 1
tie(img1_min_x, img1_min_y,img1_max_x,img1_max_y) = minMaxCorners(image1dst);
cout << "Image 1: Min x " << img1_min_x << " Min y " << img1_min_y << " Max x " << img1_max_x << " Max y " << img1_max_y << endl;
//New coordinates for iamge 2
tie(img2_min_x, img2_min_y,img2_max_x,img2_max_y) = minMaxCorners(image2dst);
cout << "Image 2: Min x " << img2_min_x << " Min y " << img2_min_y << " Max x " << img2_max_x << " Max y " << img2_max_y << endl;
//determine bounding area for resulting images
result_min_x = min(img1_min_x, img2_min_x);
result_max_x = max(img1_max_x, img2_max_x);
result_min_y = min(img1_min_y, img2_min_y);
result_max_y = max(img1_max_y, img2_max_y);
cout << "Result Image: Min x " << result_min_x << " Min y " << result_min_y << " Max x " << result_max_x << " Max y " << result_max_y << endl;
//Determine size of padded result (blank image) to be used for stitching
result_x = (abs(floor(result_min_x)) + abs(ceil(result_max_x)));
result_y = (abs(floor(result_min_y)) + abs(ceil(result_max_y)));
result = Mat(Size(result_x,result_y), CV_32FC1,Scalar(0,0,0));
//-Move the images to the postiive by creating a matrix to represent the translation
int anchor_x, anchor_y = 0;
Mat translation = Mat::eye(3,3,CV_64F);
if(result_min_x < 0){
anchor_x = (int) floor(result_min_x);
translation.at<double>(0,2) -= anchor_x;
}
if(result_min_y < 0){
anchor_y = (int) floor(result_min_y);
translation.at<double>(1,2) -= anchor_y;
}
cout << translation << endl;
//Warp each image accordingly to the new padded result image
warpPerspective(image2, result, translation, result.size(), INTER_LINEAR, BORDER_TRANSPARENT, 0);
warpPerspective(image1, result, (translation*homography), result.size(), INTER_LINEAR, BORDER_TRANSPARENT,0);
vector<Point2f> fourCorners(Mat image){
vector<Point2f> corners;
corners.push_back(Point2f (0,0));
corners.push_back(Point2f (image.size().width,0));
corners.push_back(Point2f (0, image.size().height));
corners.push_back(Point2f (image.size().width, image.size().height));
return(corners);
}
tuple<float, float, float, float> minMaxCorners(vector<Point2f> imageMatrix){
float min_x1, min_x2, min_y1, min_y2, max_x1, max_x2, max_y1, max_y2,img_min_x, img_min_y, img_max_x, img_max_y;
min_x1 = min(imageMatrix.at(0).x, imageMatrix.at(1).x);
min_x2 = min(imageMatrix.at(2).x, imageMatrix.at(3).x);
min_y1 = min(imageMatrix.at(0).y, imageMatrix.at(1).y);
min_y2 = min(imageMatrix.at(2).y, imageMatrix.at(3).y);
max_x1 = max(imageMatrix.at(0).x, imageMatrix.at(1).x);
max_x2 = max(imageMatrix.at(2).x, imageMatrix.at(3).x);
max_y1 = max(imageMatrix.at(0).y, imageMatrix.at(1).y);
max_y2 = max(imageMatrix.at(2).y, imageMatrix.at(3).y);
img_min_x = min(min_x1, min_x2);
img_min_y = min(min_y1, min_y2);
img_max_x = max(max_x1, max_x2);
img_max_y = max(max_y1, max_y2);
return{img_min_x,img_min_y, img_max_x, img_max_y };
}
EDIT I am not sure but it only happens sometimes as you can see in the following image.