improve NMS implementation (#1173)

corelib/src/util2d.cpp

@@ -2118,6 +2118,7 @@ void NMS(
  cv::Mat inds = cv::Mat(cv::Size(img_width, img_height), CV_16UC1);
 
  cv::Mat confidence = cv::Mat(cv::Size(img_width, img_height), CV_32FC1);
+ cv::Mat dilated_conf = cv::Mat(cv::Size(img_width, img_height), CV_32FC1);
 
  grid.setTo(0);
  inds.setTo(0);
@@ -2134,11 +2135,8 @@ void NMS(
  confidence.at<float>(vv, uu) = ptsIn[i].response;
  }
 
- // debug
- //cv::Mat confidenceVis = confidence.clone() * 255;
- //confidenceVis.convertTo(confidenceVis, CV_8UC1);
- //cv::imwrite("confidence.bmp", confidenceVis);
- //cv::imwrite("grid_in.bmp", grid);
+ cv::dilate(confidence, dilated_conf, cv::Mat());
+ cv::Mat peaks = confidence == dilated_conf;
 
  cv::copyMakeBorder(grid, grid, dist_thresh, dist_thresh, dist_thresh, dist_thresh, cv::BORDER_CONSTANT, 0);
 
@@ -2151,20 +2149,25 @@ void NMS(
 
  if (grid.at<unsigned char>(vv, uu) == 100) // If not yet suppressed.
  {
- for(int k = -dist_thresh; k < (dist_thresh+1); k++)
+ if (peaks.at<unsigned char>(vv-dist_thresh, uu-dist_thresh) == 255)
  {
- for(int j = -dist_thresh; j < (dist_thresh+1); j++)
+ for(int k = -dist_thresh; k < (dist_thresh+1); k++)
  {
- if((j==0 && k==0) || grid.at<unsigned char>(vv + k, uu + j) == 0)
- continue;
-
- if ( confidence.at<float>(vv + k - dist_thresh, uu + j - dist_thresh) <= c )
+ for(int j = -dist_thresh; j < (dist_thresh+1); j++)
  {
- grid.at<unsigned char>(vv + k, uu + j) = 0;
+ if ((j==0 && k==0) || grid.at<unsigned char>(vv + k, uu + j) == 0)
+ continue;
+
+ if (confidence.at<float>(vv + k - dist_thresh, uu + j - dist_thresh) <= c)
+ grid.at<unsigned char>(vv + k, uu + j) = 0;
  }
  }
+ grid.at<unsigned char>(vv, uu) = 255;
+ }
+ else
+ {
+ grid.at<unsigned char>(vv, uu) = 0;
  }
- grid.at<unsigned char>(vv, uu) = 255;
  }
  }
 
@@ -2173,9 +2176,6 @@ void NMS(
 
  grid = cv::Mat(grid, cv::Rect(dist_thresh, dist_thresh, img_width, img_height));
 
- //debug
- //cv::imwrite("grid_nms.bmp", grid);
-
  for (int v = 0; v < img_height; v++)
  {
  for (int u = 0; u < img_width; u++)