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Improve FinderPatternFinder.selectBestPatterns (#1158)

* rewrite FinderPatternFinder.selectBestPatterns
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makiuchi-d authored and srowen committed Apr 18, 2019
1 parent 0e8c46e commit 653ac2a3beb11481eff82e7d5f2bab8a745f7fac
@@ -23,6 +23,7 @@ Chang Hyun Park
Christian Brunschen (Google)
Christoph Schulz (creatale GmbH)
crowdin.net
Daisuke Makiuchi
Daniel Switkin (Google)
Dave MacLachlan (Google)
David Phillip Oster (Google)
@@ -24,6 +24,7 @@

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
@@ -40,6 +41,7 @@
public class FinderPatternFinder {

private static final int CENTER_QUORUM = 2;
private static final EstimatedModuleComparator moduleComparator = new EstimatedModuleComparator();
protected static final int MIN_SKIP = 3; // 1 pixel/module times 3 modules/center
protected static final int MAX_MODULES = 97; // support up to version 20 for mobile clients

@@ -590,10 +592,18 @@ private boolean haveMultiplyConfirmedCenters() {
return totalDeviation <= 0.05f * totalModuleSize;
}

/**
* Get square of distance between a and b.
*/
private static double squaredDistance(FinderPattern a, FinderPattern b) {
double x = a.getX() - b.getX();
double y = a.getY() - b.getY();
return x * x + y * y;
}

/**
* @return the 3 best {@link FinderPattern}s from our list of candidates. The "best" are
* those that have been detected at least {@link #CENTER_QUORUM} times, and whose module
* size differs from the average among those patterns the least
* those have similar module size and form a shape closer to a isosceles right triangle.
* @throws NotFoundException if 3 such finder patterns do not exist
*/
private FinderPattern[] selectBestPatterns() throws NotFoundException {
@@ -604,85 +614,63 @@ private boolean haveMultiplyConfirmedCenters() {
throw NotFoundException.getNotFoundInstance();
}

// 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
double totalModuleSize = 0.0;
double square = 0.0;
for (FinderPattern center : possibleCenters) {
float size = center.getEstimatedModuleSize();
totalModuleSize += size;
square += (double) size * size;
}
double average = totalModuleSize / startSize;
float stdDev = (float) Math.sqrt(square / startSize - average * average);
Collections.sort(possibleCenters, moduleComparator);

Collections.sort(possibleCenters, new FurthestFromAverageComparator((float) average));
double distortion = Double.MAX_VALUE;
double[] squares = new double[3];
FinderPattern[] bestPatterns = new FinderPattern[3];

float limit = Math.max(0.2f * (float) average, stdDev);
for (int i = 0; i < possibleCenters.size() - 2; i++) {
FinderPattern fpi = possibleCenters.get(i);
float minModuleSize = fpi.getEstimatedModuleSize();

for (int i = 0; i < possibleCenters.size() && possibleCenters.size() > 3; i++) {
FinderPattern pattern = possibleCenters.get(i);
if (Math.abs(pattern.getEstimatedModuleSize() - average) > limit) {
possibleCenters.remove(i);
i--;
}
}
}
for (int j = i + 1; j < possibleCenters.size() - 1; j++) {
FinderPattern fpj = possibleCenters.get(j);
double squares0 = squaredDistance(fpi, fpj);

if (possibleCenters.size() > 3) {
// Throw away all but those first size candidate points we found.
for (int k = j + 1; k < possibleCenters.size(); k++) {
FinderPattern fpk = possibleCenters.get(k);
float maxModuleSize = fpk.getEstimatedModuleSize();
if (maxModuleSize > minModuleSize * 1.4f) {
// module size is not similar
continue;
}

float totalModuleSize = 0.0f;
for (FinderPattern possibleCenter : possibleCenters) {
totalModuleSize += possibleCenter.getEstimatedModuleSize();
squares[0] = squares0;
squares[1] = squaredDistance(fpj, fpk);
squares[2] = squaredDistance(fpi, fpk);
Arrays.sort(squares);

// a^2 + b^2 = c^2 (Pythagorean theorem), and a = b (isosceles triangle).
// Since any right triangle satisfies the formula c^2 - b^2 - a^2 = 0,
// we need to check both two equal sides separately.
// The value of |c^2 - 2 * b^2| + |c^2 - 2 * a^2| increases as dissimilarity
// from isosceles right triangle.
double d = Math.abs(squares[2] - 2 * squares[1]) + Math.abs(squares[2] - 2 * squares[0]);
if (d < distortion) {
distortion = d;
bestPatterns[0] = fpi;
bestPatterns[1] = fpj;
bestPatterns[2] = fpk;
}
}
}

float average = totalModuleSize / possibleCenters.size();

Collections.sort(possibleCenters, new CenterComparator(average));

possibleCenters.subList(3, possibleCenters.size()).clear();
}

return new FinderPattern[]{
possibleCenters.get(0),
possibleCenters.get(1),
possibleCenters.get(2)
};
}

/**
* <p>Orders by furthest from average</p>
*/
private static final class FurthestFromAverageComparator implements Comparator<FinderPattern>, Serializable {
private final float average;
private FurthestFromAverageComparator(float f) {
average = f;
}
@Override
public int compare(FinderPattern center1, FinderPattern center2) {
return Float.compare(Math.abs(center2.getEstimatedModuleSize() - average),
Math.abs(center1.getEstimatedModuleSize() - average));
if (distortion == Double.MAX_VALUE) {
throw NotFoundException.getNotFoundInstance();
}

return bestPatterns;
}

/**
* <p>Orders by {@link FinderPattern#getCount()}, descending.</p>
* <p>Orders by {@link FinderPatternFinder#getEstimatedModuleSize()}</p>
*/
private static final class CenterComparator implements Comparator<FinderPattern>, Serializable {
private final float average;
private CenterComparator(float f) {
average = f;
}
private static final class EstimatedModuleComparator implements Comparator<FinderPattern>, Serializable {
@Override
public int compare(FinderPattern center1, FinderPattern center2) {
int countCompare = Integer.compare(center2.getCount(), center1.getCount());
if (countCompare == 0) {
return Float.compare(Math.abs(center1.getEstimatedModuleSize() - average),
Math.abs(center2.getEstimatedModuleSize() - average));
}
return countCompare;
return Float.compare(center1.getEstimatedModuleSize(), center2.getEstimatedModuleSize());
}
}

@@ -28,7 +28,7 @@
public QRCodeBlackBox2TestCase() {
super("src/test/resources/blackbox/qrcode-2", new MultiFormatReader(), BarcodeFormat.QR_CODE);
addTest(31, 31, 0.0f);
addTest(29, 29, 90.0f);
addTest(30, 30, 90.0f);
addTest(30, 30, 180.0f);
addTest(30, 30, 270.0f);
}

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