selectable match confidence for detection/stitching (#66)

relation to distance ratio from Lowe's paper: match confidence = 1 - (distance ratio)

xpano/algorithm/algorithm.cc

@@ -14,6 +14,7 @@
 #include <opencv2/features2d.hpp>
 #include <opencv2/photo.hpp>
 #include <opencv2/stitching.hpp>
+#include <opencv2/stitching/detail/matchers.hpp>
 
 #include "xpano/algorithm/auto_crop.h"
 #include "xpano/algorithm/image.h"
@@ -85,7 +86,8 @@ std::optional<cv::RotateFlags> GetRotationFlags(ProjectionOptions options) {
 
 }  // namespace
 
-std::vector<cv::DMatch> MatchImages(const Image& img1, const Image& img2) {
+std::vector<cv::DMatch> MatchImages(const Image& img1, const Image& img2,
+                                    float match_conf) {
   if (img1.GetKeypoints().empty() || img2.GetKeypoints().empty()) {
     return {};
   }
@@ -98,8 +100,7 @@ std::vector<cv::DMatch> MatchImages(const Image& img1, const Image& img2) {
   // FILTER BY FIRST/SECOND RATIO
   std::vector<cv::DMatch> good_matches;
   for (const auto& match : matches) {
-    double ratio = match[0].distance / match[1].distance;
-    if (ratio < 0.8) {
+    if (match[0].distance < (1.0f - match_conf) * match[1].distance) {
       good_matches.push_back(match[0]);
     }
   }
@@ -187,6 +188,8 @@ StitchResult Stitch(const std::vector<cv::Mat>& images, StitchOptions options,
       stitcher->setFeaturesFinder(cv::ORB::create());
       break;
   }
+  stitcher->setFeaturesMatcher(cv::makePtr<cv::detail::BestOf2NearestMatcher>(
+      false, options.match_conf));
 
   cv::Mat pano;
   auto status = stitcher->stitch(images, pano);

xpano/algorithm/algorithm.h

@@ -25,7 +25,8 @@ struct Match {
   std::vector<cv::DMatch> matches;
 };
 
-std::vector<cv::DMatch> MatchImages(const Image& img1, const Image& img2);
+std::vector<cv::DMatch> MatchImages(const Image& img1, const Image& img2,
+                                    float match_conf);
 
 std::vector<Pano> FindPanos(const std::vector<Match>& matches,
                             int match_threshold);
@@ -76,6 +77,7 @@ struct ProjectionOptions {
 struct StitchOptions {
   ProjectionOptions projection;
   FeatureType feature = FeatureType::kSift;
+  float match_conf = kDefaultMatchConf;
 };
 
 struct StitchResult {

xpano/constants.h

@@ -65,6 +65,9 @@ constexpr int kStepPreviewLongerSide = 256;
 
 constexpr float kDefaultPaniniA = 2.0f;
 constexpr float kDefaultPaniniB = 1.0f;
+constexpr float kDefaultMatchConf = 0.25f;
+constexpr float kMinMatchConf = 0.1f;
+constexpr float kMaxMatchConf = 0.4f;
 
 const std::string kConfigFilename = "config.txt";
 

xpano/gui/panels/sidebar.cc

@@ -100,7 +100,30 @@ void DrawLoadingOptionsMenu(pipeline::LoadingOptions* loading_options) {
   }
 }
 
-void DrawMatchingOptionsMenu(pipeline::MatchingOptions* matching_options) {
+bool DrawMatchConf(float* match_conf) {
+  bool value_changed = false;
+  if (ImGui::InputFloat("Match confidence", match_conf, 0.01f, 0.01f, "%.2f")) {
+    value_changed = true;
+
+    if (*match_conf < kMinMatchConf) {
+      *match_conf = kMinMatchConf;
+    }
+
+    if (*match_conf > kMaxMatchConf) {
+      *match_conf = kMaxMatchConf;
+    }
+  }
+  ImGui::SameLine();
+  utils::imgui::InfoMarker(
+      "(?)",
+      "Increasing this value will get less matches, but with higher quality."
+      "\nChanging both ways can be useful in case a panorama fails to detect "
+      "or stitch.");
+  return value_changed;
+}
+
+void DrawMatchingOptionsMenu(pipeline::MatchingOptions* matching_options,
+                             bool debug_enabled) {
   if (ImGui::BeginMenu("Panorama detection")) {
     ImGui::Text(
         "Experiment with this if the app cannot find the panoramas you "
@@ -121,6 +144,10 @@ void DrawMatchingOptionsMenu(pipeline::MatchingOptions* matching_options) {
         "(?)",
         "Number of keypoints that need to match in order to include the two "
         "images in a panorama.");
+    if (debug_enabled) {
+      ImGui::Text("[debug options]");
+      DrawMatchConf(&matching_options->match_conf);
+    }
     ImGui::EndMenu();
   }
 }
@@ -181,7 +208,12 @@ Action DrawStitchOptionsMenu(pipeline::StitchAlgorithmOptions* stitch_options,
     action |= DrawProjectionOptions(stitch_options);
 
     if (debug_enabled) {
+      ImGui::Text("[debug options]");
       action |= DrawFeatureMatchingOptions(stitch_options);
+
+      if (DrawMatchConf(&stitch_options->match_conf)) {
+        action |= {ActionType::kRecomputePano};
+      }
     }
     ImGui::EndMenu();
   }
@@ -190,6 +222,7 @@ Action DrawStitchOptionsMenu(pipeline::StitchAlgorithmOptions* stitch_options,
 
 void DrawAutofillOptionsMenu(pipeline::InpaintingOptions* inpaint_options) {
   if (ImGui::BeginMenu("Auto fill")) {
+    ImGui::Text("[debug options]");
     ImGui::Text("Algorithm:");
     ImGui::Spacing();
     if (ImGui::BeginCombo("##inpaint_type", Label(inpaint_options->method))) {
@@ -224,7 +257,7 @@ Action DrawOptionsMenu(pipeline::CompressionOptions* compression_options,
   if (ImGui::BeginMenu("Options")) {
     DrawCompressionOptionsMenu(compression_options);
     DrawLoadingOptionsMenu(loading_options);
-    DrawMatchingOptionsMenu(matching_options);
+    DrawMatchingOptionsMenu(matching_options, debug_enabled);
     action |= DrawStitchOptionsMenu(stitch_options, debug_enabled);
     if (debug_enabled) {
       DrawAutofillOptionsMenu(inpaint_options);

xpano/pipeline/stitcher_pipeline.cc

@@ -238,8 +238,10 @@ StitcherData StitcherPipeline::RunMatchingPipeline(
   for (int j = 0; j < images.size(); j++) {
     for (int i = std::max(0, j - num_neighbors); i < j; i++) {
       matches_future.push_back(
-          pool_.submit([this, i, j, left = images[i], right = images[j]]() {
-            auto match = algorithm::Match{i, j, MatchImages(left, right)};
+          pool_.submit([this, i, j, left = images[i], right = images[j],
+                        match_conf = options.match_conf]() {
+            auto match =
+                algorithm::Match{i, j, MatchImages(left, right, match_conf)};
             progress_.NotifyTaskDone();
             return match;
           }));

xpano/pipeline/stitcher_pipeline.h

@@ -30,6 +30,7 @@ struct CompressionOptions {
 struct MatchingOptions {
   int neighborhood_search_size = kDefaultNeighborhoodSearchSize;
   int match_threshold = kDefaultMatchThreshold;
+  float match_conf = kDefaultMatchConf;
 };
 
 struct LoadingOptions {