From c5357cc17c0149ec9190cbcaf7a2409a6b1c709c Mon Sep 17 00:00:00 2001
From: Alexey Spizhevoy <no@email>
Date: Fri, 30 Sep 2011 12:46:11 +0000
Subject: [PATCH] Added fix for removing too similar images into the stitching
 module

---
 modules/stitching/src/matchers.cpp          | 14 +++++++-------
 modules/stitching/src/motion_estimators.cpp |  7 ++++---
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/modules/stitching/src/matchers.cpp b/modules/stitching/src/matchers.cpp
index f37fb467b..a720c6a63 100644
--- a/modules/stitching/src/matchers.cpp
+++ b/modules/stitching/src/matchers.cpp
@@ -427,12 +427,6 @@ void BestOf2NearestMatcher::match(const ImageFeatures &features1, const ImageFea
 {
     (*impl_)(features1, features2, matches_info);
 
-    //Mat out;
-    //drawMatches(features1.img, features1.keypoints, features2.img, features2.keypoints, matches_info.matches, out);
-    //stringstream ss;
-    //ss << features1.img_idx << features2.img_idx << ".png";
-    //imwrite(ss.str(), out);
-
     // Check if it makes sense to find homography
     if (matches_info.matches.size() < static_cast<size_t>(num_matches_thresh1_))
         return;
@@ -466,7 +460,13 @@ void BestOf2NearestMatcher::match(const ImageFeatures &features1, const ImageFea
         if (matches_info.inliers_mask[i])
             matches_info.num_inliers++;
 
-    matches_info.confidence = matches_info.num_inliers / (8 + 0.3*matches_info.matches.size());
+    // These coeffs are from paper M. Brown and D. Lowe. "Automatic Panoramic Image Stitching 
+    // using Invariant Features"
+    matches_info.confidence = matches_info.num_inliers / (8 + 0.3 * matches_info.matches.size());
+
+    // Set zero confidence to remove matches between too close images, as they don't provide 
+    // additional information anyway. The threshold was set experimentally.
+    matches_info.confidence = matches_info.confidence > 3. ? 0. : matches_info.confidence;
 
     // Check if we should try to refine motion
     if (matches_info.num_inliers < num_matches_thresh2_)
diff --git a/modules/stitching/src/motion_estimators.cpp b/modules/stitching/src/motion_estimators.cpp
index 74ff57954..e8ebd1a6d 100644
--- a/modules/stitching/src/motion_estimators.cpp
+++ b/modules/stitching/src/motion_estimators.cpp
@@ -748,11 +748,12 @@ vector<int> leaveBiggestComponent(vector<ImageFeatures> &features,  vector<Match
     if (static_cast<int>(features_subset.size()) == num_images)
         return indices;
 
-    LOG("Removed some images, because can't match them: (");
-    LOG(indices_removed[0]+1);
+    LOG("Removed some images, because can't match them or there are too similar images: (");
+    LOG(indices_removed[0] + 1);
     for (size_t i = 1; i < indices_removed.size(); ++i) 
         LOG(", " << indices_removed[i]+1);
-    LOGLN("). Try to decrease --match_conf value.");
+    LOGLN(").");
+    LOGLN("Try to decrease --match_conf value and/or check if you're stitching duplicates.");
 
     features = features_subset;
     pairwise_matches = pairwise_matches_subset;