From 3675cd82abadceb3d1d032092b1f7698fd8e6712 Mon Sep 17 00:00:00 2001
From: Matt Hill <matthill@openalpr.com>
Date: Fri, 25 Sep 2015 20:34:11 -0400
Subject: [PATCH] Calculating char gap by distance from midpoint (rather than
 edge). More accurate for characters like "1" that don't fill up the full
 area, but still have the same distance between overall characters

---
 .../segmentation/charactersegmenter.cpp       | 21 +++++++++++++------
 .../segmentation/charactersegmenter.h         |  2 ++
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/src/openalpr/segmentation/charactersegmenter.cpp b/src/openalpr/segmentation/charactersegmenter.cpp
index 144edac..f4d467c 100644
--- a/src/openalpr/segmentation/charactersegmenter.cpp
+++ b/src/openalpr/segmentation/charactersegmenter.cpp
@@ -403,6 +403,11 @@ namespace alpr
       }
     }
   }
+  int CharacterSegmenter::getCharGap(cv::Rect leftBox, cv::Rect rightBox) {
+      int right_midpoint = (rightBox.x + (rightBox.width / 2));
+      int left_midpoint = (leftBox.x + (leftBox.width / 2));
+      return  right_midpoint - left_midpoint;
+  }
 
   vector<Rect> CharacterSegmenter::combineCloseBoxes( vector<Rect> charBoxes)
   {
@@ -410,7 +415,7 @@ namespace alpr
     if (charBoxes.size() <= 2)
       return charBoxes;
     
-    // First find the median char gap (the space between characters)
+    // First find the median char gap (the space from midpoint to midpoint of chars)
     
     vector<int> char_gaps;
     for (unsigned int i = 0; i < charBoxes.size(); i++)
@@ -419,8 +424,7 @@ namespace alpr
         break;
       
       // the space between charbox i and i+1
-      int char_gap = charBoxes[i+1].x - (charBoxes[i].x + charBoxes[i].width);
-      char_gaps.push_back(char_gap);
+      char_gaps.push_back(getCharGap(charBoxes[i], charBoxes[i+1]));
     }
         
     int median_char_gap = median(char_gaps.data(), char_gaps.size());
@@ -455,14 +459,14 @@ namespace alpr
       if (i == 0)
         left_gap = 999999999999;
       else
-        left_gap = charBoxes[i].x - (charBoxes[i-1].x + charBoxes[i-1].width);
+        left_gap = getCharGap(charBoxes[i-1], charBoxes[i]);
       
-      right_gap = charBoxes[i+1].x - (charBoxes[i].x + charBoxes[i].width);
+      right_gap = getCharGap(charBoxes[i], charBoxes[i+1]);
       
       int min_gap = (int) ((float)median_char_gap) * 0.75;
       int max_gap = (int) ((float)median_char_gap) * 1.25;
       
-      int max_width = (int) ((float)biggestCharWidth) * 1.1;
+      int max_width = (int) ((float)biggestCharWidth) * 1.2;
       
       bool has_good_gap = (left_gap >= min_gap && left_gap <= max_gap) || (right_gap >= min_gap && right_gap <= max_gap);
       
@@ -488,6 +492,11 @@ namespace alpr
       else
       {
         newCharBoxes.push_back(charBoxes[i]);
+        if (this->config->debugCharSegmenter)
+        {
+          cout << "Not Merging 2 boxes -- " << i << " and " << i + 1 << " -- has_good_gap: " << has_good_gap <<
+                  " bigWidth (" << bigWidth << ") > max_width ("  << max_width << ")" << endl;
+        }
       }
     }
 
diff --git a/src/openalpr/segmentation/charactersegmenter.h b/src/openalpr/segmentation/charactersegmenter.h
index 5bdb988..b6c9565 100644
--- a/src/openalpr/segmentation/charactersegmenter.h
+++ b/src/openalpr/segmentation/charactersegmenter.h
@@ -68,6 +68,8 @@ namespace alpr
 
       std::vector<cv::Rect> getHistogramBoxes(HistogramVertical histogram, float avgCharWidth, float avgCharHeight, float* score);
       std::vector<cv::Rect> getBestCharBoxes(cv::Mat img, std::vector<cv::Rect> charBoxes, float avgCharWidth);
+      
+      int getCharGap(cv::Rect leftBox, cv::Rect rightBox);
       std::vector<cv::Rect> combineCloseBoxes( std::vector<cv::Rect> charBoxes);
 
       std::vector<cv::Rect> get1DHits(cv::Mat img, int yOffset);