additionally filter contours by their size

this allows filtering out some false-positives which were so far
incorrectly recognized as bananas.

Author: Nic822

include/banana-lib/lib.hpp

@@ -118,6 +118,12 @@ namespace banana {
             /// Maximum score of `cv::matchShapes` which we still accept as a banana.
             float const match_max_score{0.6f};
 
+            /// Minimum area value of a banana (in px^2).
+            float const min_area{1e5f};
+
+            /// Maximum area value of a banana (in px^2).
+            float const max_area{1e7f};
+
             /// How long (in pixels) is a meter? This is the extrinsic calibration needed to calculate sizes.
             double const pixels_per_meter;
 

resources/test-images/banana-30.jpg

@@ -106,15 +106,19 @@ namespace banana {
     }
 
     auto Analyzer::IsBananaContour(Contour const& contour) const -> bool {
-        return cv::matchShapes(contour, this->reference_contour_, cv::CONTOURS_MATCH_I1, 0.0) > this->settings_.match_max_score;
+        if (cv::matchShapes(contour, this->reference_contour_, cv::CONTOURS_MATCH_I1, 0.0) > this->settings_.match_max_score) {
+            return false;
+        }
+        auto const area = cv::contourArea(contour);
+        return settings_.min_area < area && area < settings_.max_area;
     }
 
     auto Analyzer::FindBananaContours(cv::Mat const& image) const -> Contours {
         auto filtered_image = ColorFilter(image, settings_.filter_lower_threshold_color, settings_.filter_upper_threshold_color);
         SHOW_DEBUG_IMAGE(filtered_image, "color filtered image");
 
         // Removing noise
-        auto const kernel = cv::getStructuringElement(cv::MORPH_RECT, cv::Size(5, 5));
+        auto const kernel = cv::getStructuringElement(cv::MORPH_RECT, {5, 5});
         cv::morphologyEx(filtered_image, filtered_image, cv::MORPH_OPEN, kernel);
         SHOW_DEBUG_IMAGE(filtered_image, "morph");
 
@@ -126,7 +130,7 @@ namespace banana {
         cv::findContours(filtered_image, contours, cv::RETR_EXTERNAL, cv::CHAIN_APPROX_SIMPLE);
 
         std::erase_if(contours, [this](auto const& contour) -> auto {
-            return this->IsBananaContour(contour);
+            return !this->IsBananaContour(contour);
         });
 
         return contours;