stitching: use BORDER_CONSTANT in warp

modules/stitching/src/stitcher.cpp

@@ -179,7 +179,7 @@ Stitcher::Status Stitcher::composePanorama(InputArrayOfArrays images, OutputArra
         K(1,1) *= (float)seam_work_aspect_;
         K(1,2) *= (float)seam_work_aspect_;
 
-        corners[i] = w->warp(seam_est_imgs_[i], K, cameras_[i].R, INTER_LINEAR, BORDER_REFLECT, images_warped[i]);
+        corners[i] = w->warp(seam_est_imgs_[i], K, cameras_[i].R, INTER_LINEAR, BORDER_CONSTANT, images_warped[i]);
         sizes[i] = images_warped[i].size();
 
         w->warp(masks[i], K, cameras_[i].R, INTER_NEAREST, BORDER_CONSTANT, masks_warped[i]);
@@ -271,7 +271,7 @@ Stitcher::Status Stitcher::composePanorama(InputArrayOfArrays images, OutputArra
         cameras_[img_idx].K().convertTo(K, CV_32F);
 
         // Warp the current image
-        w->warp(img, K, cameras_[img_idx].R, INTER_LINEAR, BORDER_REFLECT, img_warped);
+        w->warp(img, K, cameras_[img_idx].R, INTER_LINEAR, BORDER_CONSTANT, img_warped);
 
         // Warp the current image mask
         mask.create(img_size, CV_8U);