Merge pull request #19859 from danielenricocahall:fix-blob-detector-single-thresh

Fix Single ThresholdBug in Simple Blob Detector

* address bug with using min dist between blobs in blob detector

cast type in comparison and remove docs

address bug with using min dist between blobs in blob detector

use scalar instead of int

address bug with using min dist between blobs in blob detector

* fix namespace and formatting

modules/features2d/src/blobdetector.cpp

@@ -325,13 +325,19 @@ void SimpleBlobDetectorImpl::detect(InputArray image, std::vector<cv::KeyPoint>&
 
         std::vector < Center > curCenters;
         findBlobs(grayscaleImage, binarizedImage, curCenters);
+        if(params.maxThreshold - params.minThreshold <= params.thresholdStep) {
+            // if the difference between min and max threshold is less than the threshold step
+            // we're only going to enter the loop once, so we need to add curCenters
+            // to ensure we still use minDistBetweenBlobs
+            centers.push_back(curCenters);
+        }
         std::vector < std::vector<Center> > newCenters;
         for (size_t i = 0; i < curCenters.size(); i++)
         {
             bool isNew = true;
             for (size_t j = 0; j < centers.size(); j++)
             {
-                double dist = norm(centers[j][ centers[j].size() / 2 ].location - curCenters[i].location);
+                double dist = norm(centers[j][centers[j].size() / 2 ].location - curCenters[i].location);
                 isNew = dist >= params.minDistBetweenBlobs && dist >= centers[j][ centers[j].size() / 2 ].radius && dist >= curCenters[i].radius;
                 if (!isNew)
                 {

modules/features2d/test/test_blobdetector.cpp

@@ -0,0 +1,21 @@
+// This file is part of OpenCV project.
+// It is subject to the license terms in the LICENSE file found in the top-level directory
+// of this distribution and at http://opencv.org/license.html.
+
+#include "test_precomp.hpp"
+
+namespace opencv_test { namespace {
+TEST(Features2d_BlobDetector, bug_6667)
+{
+    cv::Mat image = cv::Mat(cv::Size(100, 100), CV_8UC1, cv::Scalar(255, 255, 255));
+    cv::circle(image, Point(50, 50), 20, cv::Scalar(0), -1);
+    SimpleBlobDetector::Params params;
+    params.minThreshold = 250;
+    params.maxThreshold = 260;
+    std::vector<KeyPoint> keypoints;
+
+    Ptr<SimpleBlobDetector> detector = SimpleBlobDetector::create(params);
+    detector->detect(image, keypoints);
+    ASSERT_NE((int) keypoints.size(), 0);
+}
+}} // namespace