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Improve detector logic to throw out false positive finder patterns in a more reasonable manner. Current logic didn't quite achieve its goal in some corner cases and needed rethinking and some simplification. Fixes a reported failure from the group list. Net change in passed test cases is -1 otherwise (for 270 degree rotation -- not vital) so I consider it a net tiny win.

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git-svn-id: https://zxing.googlecode.com/svn/trunk@1039 59b500cc-1b3d-0410-9834-0bbf25fbcc57
This commit is contained in:
srowen 2009-08-23 15:32:01 +00:00
parent 362236564e
commit e1dd41a115
2 changed files with 25 additions and 33 deletions
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52
core/src/com/google/zxing/qrcode/detector/FinderPatternFinder.java
View file

@ -463,7 +463,7 @@ public class FinderPatternFinder {
// 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.
// 5% of the total module size estimates, it's too much.
float average = totalModuleSize / (float) max;
float totalDeviation = 0.0f;
for (int i = 0; i < max; i++) {
@ -480,25 +480,35 @@ public class FinderPatternFinder {
* @throws ReaderException if 3 such finder patterns do not exist
*/
private FinderPattern[] selectBestPatterns() throws ReaderException {
if (possibleCenters.size() < 3) {
int startSize = possibleCenters.size();
if (startSize < 3) {
// Couldn't find enough finder patterns
throw ReaderException.getInstance();
}
Collections.insertionSort(possibleCenters, new CenterComparator());
// Filter outlier possibilities whose module size is too different
if (startSize > 3) {
// But we can only afford to do so if we have at least 4 possibilities to choose from
float totalModuleSize = 0.0f;
for (int i = 0; i < startSize; i++) {
totalModuleSize += ((FinderPattern) possibleCenters.get(i)).getEstimatedModuleSize();
}
float average = totalModuleSize / (float) startSize;
for (int i = 0; i < possibleCenters.size() && possibleCenters.size() > 3; i++) {
FinderPattern pattern = (FinderPattern) possibleCenters.get(i);
if (Math.abs(pattern.getEstimatedModuleSize() - average) > 0.2f * average) {
possibleCenters.remove(i);
i--;
}
}
}
if (possibleCenters.size() > 3) {
// Throw away all but those first size candidate points we found.
Collections.insertionSort(possibleCenters, new CenterComparator());
possibleCenters.setSize(3);
}
// We need to pick the best three. Find the most
// popular ones whose module size is nearest the average
float averageModuleSize = 0.0f;
for (int i = 0; i < 3; i++) {
averageModuleSize += ((FinderPattern) possibleCenters.elementAt(i)).getEstimatedModuleSize();
}
averageModuleSize /= 3.0f;
// We don't have java.util.Collections in J2ME
Collections.insertionSort(possibleCenters, new ClosestToAverageComparator(averageModuleSize));
return new FinderPattern[]{
(FinderPattern) possibleCenters.elementAt(0),
@ -516,22 +526,4 @@ public class FinderPatternFinder {
}
}
/**
* <p>Orders by variance from average module size, ascending.</p>
*/
private static class ClosestToAverageComparator implements Comparator {
private final float averageModuleSize;
private ClosestToAverageComparator(float averageModuleSize) {
this.averageModuleSize = averageModuleSize;
}
public int compare(Object center1, Object center2) {
return Math.abs(((FinderPattern) center1).getEstimatedModuleSize() - averageModuleSize) <
Math.abs(((FinderPattern) center2).getEstimatedModuleSize() - averageModuleSize) ?
-1 :
1;
}
}
}

6
core/test/src/com/google/zxing/qrcode/QRCodeBlackBox2TestCase.java
View file

@ -28,9 +28,9 @@ public final class QRCodeBlackBox2TestCase extends AbstractBlackBoxTestCase {
public QRCodeBlackBox2TestCase() {
super("test/data/blackbox/qrcode-2", new MultiFormatReader(), BarcodeFormat.QR_CODE);
addTest(23, 23, 0.0f);
addTest(20, 20, 90.0f);
addTest(21, 21, 180.0f);
addTest(19, 19, 270.0f);
addTest(21, 21, 90.0f);
addTest(20, 20, 180.0f);
addTest(18, 18, 270.0f);
}
}