From 256f3125fd9ffa08e0c9e347071ef5038e9c9a28 Mon Sep 17 00:00:00 2001
From: srowen <srowen@59b500cc-1b3d-0410-9834-0bbf25fbcc57>
Date: Thu, 8 May 2008 15:12:44 +0000
Subject: [PATCH] Detector is now a little more skeptical once it has found 3
 confirmed finder patterns -- one may be a false positive, so it also checks
 to see if the estimated module sizes are "pretty similar". If not, keeps
 looking.

git-svn-id: http://zxing.googlecode.com/svn/trunk@394 59b500cc-1b3d-0410-9834-0bbf25fbcc57
---
 .../qrcode/detector/FinderPatternFinder.java  | 29 ++++++++++++++-----
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/core/src/com/google/zxing/qrcode/detector/FinderPatternFinder.java b/core/src/com/google/zxing/qrcode/detector/FinderPatternFinder.java
index 029be72d..10c0708b 100755
--- a/core/src/com/google/zxing/qrcode/detector/FinderPatternFinder.java
+++ b/core/src/com/google/zxing/qrcode/detector/FinderPatternFinder.java
@@ -419,19 +419,34 @@ final class FinderPatternFinder {
 
   /**
    * @return true iff we have found at least 3 finder patterns that have been detected
-   *         at least {@link #CENTER_QUORUM} times each
+   *         at least {@link #CENTER_QUORUM} times each, and, the estimated module size of the
+   *         candidates is "pretty similar"
    */
   private boolean haveMulitplyConfirmedCenters() {
-    int count = 0;
+    int confirmedCount = 0;
+    float totalModuleSize = 0.0f;
     int max = possibleCenters.size();
     for (int i = 0; i < max; i++) {
-      if (((FinderPattern) possibleCenters.elementAt(i)).getCount() >= CENTER_QUORUM) {
-        if (++count == 3) {
-          return true;
-        }
+      FinderPattern pattern = (FinderPattern) possibleCenters.elementAt(i);
+      if (pattern.getCount() >= CENTER_QUORUM) {
+        confirmedCount++;
+        totalModuleSize += pattern.getEstimatedModuleSize();
       }
     }
-    return false;
+    if (confirmedCount < 3) {
+      return false;
+    }
+    // OK, we have at least 3 confirmed centers, but, it's possible that one is a "false positive"
+    // and that we need to keep looking. We detect this by asking if the estimated module sizes
+    // vary too much. We arbitrarily say that when the total deviation from average exceeds
+    // 15% of the total module size estimates, it's too much.
+    float average = totalModuleSize / max;
+    float totalDeviation = 0.0f;
+    for (int i = 0; i < max; i++) {
+      FinderPattern pattern = (FinderPattern) possibleCenters.elementAt(i);
+      totalDeviation += Math.abs(pattern.getEstimatedModuleSize() - average);
+    }
+    return totalDeviation <= 0.15f * totalModuleSize;
   }
 
   /**
-- 
2.20.1