This class attempts to find finder patterns in a QR Code. Finder patterns are the square * markers at three corners of a QR Code.
* - *This class is not thread-safe and should not be reused.
+ *This class is thread-safe but not reentrant. Each thread must allocate its own object. * * @author Sean Owen */ -final class FinderPatternFinder { +public class FinderPatternFinder { private static final int CENTER_QUORUM = 2; - private static final int MIN_SKIP = 3; // 1 pixel/module times 3 modules/center - private static final int MAX_MODULES = 57; // support up to version 10 for mobile clients + protected static final int MIN_SKIP = 3; // 1 pixel/module times 3 modules/center + protected static final int MAX_MODULES = 57; // support up to version 10 for mobile clients private static final int INTEGER_MATH_SHIFT = 8; - private final MonochromeBitmapSource image; + private final BitMatrix image; private final Vector possibleCenters; private boolean hasSkipped; private final int[] crossCheckStateCount; + private final ResultPointCallback resultPointCallback; /** *
Creates a finder that will search the image for three finder patterns.
* * @param image image to search */ - FinderPatternFinder(MonochromeBitmapSource image) { + public FinderPatternFinder(BitMatrix image) { + this(image, null); + } + + public FinderPatternFinder(BitMatrix image, ResultPointCallback resultPointCallback) { this.image = image; this.possibleCenters = new Vector(); this.crossCheckStateCount = new int[5]; + this.resultPointCallback = resultPointCallback; + } + + protected BitMatrix getImage() { + return image; } - FinderPatternInfo find(Hashtable hints) throws ReaderException { + protected Vector getPossibleCenters() { + return possibleCenters; + } + + FinderPatternInfo find(Hashtable hints) throws NotFoundException { boolean tryHarder = hints != null && hints.containsKey(DecodeHintType.TRY_HARDER); int maxI = image.getHeight(); int maxJ = image.getWidth(); @@ -69,17 +83,15 @@ final class FinderPatternFinder { // image, and then account for the center being 3 modules in size. This gives the smallest // number of pixels the center could be, so skip this often. When trying harder, look for all // QR versions regardless of how dense they are. - int iSkip = (int) (maxI / (MAX_MODULES * 4.0f) * 3); + int iSkip = (3 * maxI) / (4 * MAX_MODULES); if (iSkip < MIN_SKIP || tryHarder) { iSkip = MIN_SKIP; } boolean done = false; int[] stateCount = new int[5]; - BitArray blackRow = new BitArray(maxJ); for (int i = iSkip - 1; i < maxI && !done; i += iSkip) { // Get a row of black/white values - blackRow = image.getBlackRow(i, blackRow, 0, maxJ); stateCount[0] = 0; stateCount[1] = 0; stateCount[2] = 0; @@ -87,7 +99,7 @@ final class FinderPatternFinder { stateCount[4] = 0; int currentState = 0; for (int j = 0; j < maxJ; j++) { - if (blackRow.get(j)) { + if (image.get(j, i)) { // Black pixel if ((currentState & 1) == 1) { // Counting white pixels currentState++; @@ -103,7 +115,7 @@ final class FinderPatternFinder { // expensive and didn't improve performance. iSkip = 2; if (hasSkipped) { - done = haveMulitplyConfirmedCenters(); + done = haveMultiplyConfirmedCenters(); } else { int rowSkip = findRowSkip(); if (rowSkip > stateCount[2]) { @@ -120,11 +132,13 @@ final class FinderPatternFinder { } } } else { - // Advance to next black pixel - do { - j++; - } while (j < maxJ && !blackRow.get(j)); - j--; // back up to that last white pixel + stateCount[0] = stateCount[2]; + stateCount[1] = stateCount[3]; + stateCount[2] = stateCount[4]; + stateCount[3] = 1; + stateCount[4] = 0; + currentState = 3; + continue; } // Clear state to start looking again currentState = 0; @@ -155,14 +169,14 @@ final class FinderPatternFinder { iSkip = stateCount[0]; if (hasSkipped) { // Found a third one - done = haveMulitplyConfirmedCenters(); + done = haveMultiplyConfirmedCenters(); } } } } FinderPattern[] patternInfo = selectBestPatterns(); - GenericResultPoint.orderBestPatterns(patternInfo); + ResultPoint.orderBestPatterns(patternInfo); return new FinderPatternInfo(patternInfo); } @@ -180,7 +194,7 @@ final class FinderPatternFinder { * @return true iff the proportions of the counts is close enough to the 1/1/3/1/1 ratios * used by finder patterns to be considered a match */ - private static boolean foundPatternCross(int[] stateCount) { + protected static boolean foundPatternCross(int[] stateCount) { int totalModuleSize = 0; for (int i = 0; i < 5; i++) { int count = stateCount[i]; @@ -222,22 +236,23 @@ final class FinderPatternFinder { * observed in any reading state, based on the results of the horizontal scan * @return vertical center of finder pattern, or {@link Float#NaN} if not found */ - private float crossCheckVertical(int startI, int centerJ, int maxCount, int originalStateCountTotal) { - MonochromeBitmapSource image = this.image; + private float crossCheckVertical(int startI, int centerJ, int maxCount, + int originalStateCountTotal) { + BitMatrix image = this.image; int maxI = image.getHeight(); int[] stateCount = getCrossCheckStateCount(); // Start counting up from center int i = startI; - while (i >= 0 && image.isBlack(centerJ, i)) { + while (i >= 0 && image.get(centerJ, i)) { stateCount[2]++; i--; } if (i < 0) { return Float.NaN; } - while (i >= 0 && !image.isBlack(centerJ, i) && stateCount[1] <= maxCount) { + while (i >= 0 && !image.get(centerJ, i) && stateCount[1] <= maxCount) { stateCount[1]++; i--; } @@ -245,7 +260,7 @@ final class FinderPatternFinder { if (i < 0 || stateCount[1] > maxCount) { return Float.NaN; } - while (i >= 0 && image.isBlack(centerJ, i) && stateCount[0] <= maxCount) { + while (i >= 0 && image.get(centerJ, i) && stateCount[0] <= maxCount) { stateCount[0]++; i--; } @@ -255,21 +270,21 @@ final class FinderPatternFinder { // Now also count down from center i = startI + 1; - while (i < maxI && image.isBlack(centerJ, i)) { + while (i < maxI && image.get(centerJ, i)) { stateCount[2]++; i++; } if (i == maxI) { return Float.NaN; } - while (i < maxI && !image.isBlack(centerJ, i) && stateCount[3] < maxCount) { + while (i < maxI && !image.get(centerJ, i) && stateCount[3] < maxCount) { stateCount[3]++; i++; } if (i == maxI || stateCount[3] >= maxCount) { return Float.NaN; } - while (i < maxI && image.isBlack(centerJ, i) && stateCount[4] < maxCount) { + while (i < maxI && image.get(centerJ, i) && stateCount[4] < maxCount) { stateCount[4]++; i++; } @@ -277,10 +292,11 @@ final class FinderPatternFinder { return Float.NaN; } - // If we found a finder-pattern-like section, but its size is more than 20% different than + // If we found a finder-pattern-like section, but its size is more than 40% different than // the original, assume it's a false positive - int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + stateCount[4]; - if (5 * Math.abs(stateCountTotal - originalStateCountTotal) >= originalStateCountTotal) { + int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + + stateCount[4]; + if (5 * Math.abs(stateCountTotal - originalStateCountTotal) >= 2 * originalStateCountTotal) { return Float.NaN; } @@ -292,28 +308,29 @@ final class FinderPatternFinder { * except it reads horizontally instead of vertically. This is used to cross-cross * check a vertical cross check and locate the real center of the alignment pattern. */ - private float crossCheckHorizontal(int startJ, int centerI, int maxCount, int originalStateCountTotal) { - MonochromeBitmapSource image = this.image; + private float crossCheckHorizontal(int startJ, int centerI, int maxCount, + int originalStateCountTotal) { + BitMatrix image = this.image; int maxJ = image.getWidth(); int[] stateCount = getCrossCheckStateCount(); int j = startJ; - while (j >= 0 && image.isBlack(j, centerI)) { + while (j >= 0 && image.get(j, centerI)) { stateCount[2]++; j--; } if (j < 0) { return Float.NaN; } - while (j >= 0 && !image.isBlack(j, centerI) && stateCount[1] <= maxCount) { + while (j >= 0 && !image.get(j, centerI) && stateCount[1] <= maxCount) { stateCount[1]++; j--; } if (j < 0 || stateCount[1] > maxCount) { return Float.NaN; } - while (j >= 0 && image.isBlack(j, centerI) && stateCount[0] <= maxCount) { + while (j >= 0 && image.get(j, centerI) && stateCount[0] <= maxCount) { stateCount[0]++; j--; } @@ -322,21 +339,21 @@ final class FinderPatternFinder { } j = startJ + 1; - while (j < maxJ && image.isBlack(j, centerI)) { + while (j < maxJ && image.get(j, centerI)) { stateCount[2]++; j++; } if (j == maxJ) { return Float.NaN; } - while (j < maxJ && !image.isBlack(j, centerI) && stateCount[3] < maxCount) { + while (j < maxJ && !image.get(j, centerI) && stateCount[3] < maxCount) { stateCount[3]++; j++; } if (j == maxJ || stateCount[3] >= maxCount) { return Float.NaN; } - while (j < maxJ && image.isBlack(j, centerI) && stateCount[4] < maxCount) { + while (j < maxJ && image.get(j, centerI) && stateCount[4] < maxCount) { stateCount[4]++; j++; } @@ -346,7 +363,8 @@ final class FinderPatternFinder { // If we found a finder-pattern-like section, but its size is significantly different than // the original, assume it's a false positive - int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + stateCount[4]; + int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + + stateCount[4]; if (5 * Math.abs(stateCountTotal - originalStateCountTotal) >= originalStateCountTotal) { return Float.NaN; } @@ -370,10 +388,9 @@ final class FinderPatternFinder { * @param j end of possible finder pattern in row * @return true if a finder pattern candidate was found this time */ - private boolean handlePossibleCenter(int[] stateCount, - int i, - int j) { - int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + stateCount[4]; + protected boolean handlePossibleCenter(int[] stateCount, int i, int j) { + int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + + stateCount[4]; float centerJ = centerFromEnd(stateCount, j); float centerI = crossCheckVertical(i, (int) centerJ, stateCount[2], stateCountTotal); if (!Float.isNaN(centerI)) { @@ -393,7 +410,11 @@ final class FinderPatternFinder { } } if (!found) { - possibleCenters.addElement(new FinderPattern(centerJ, centerI, estimatedModuleSize)); + ResultPoint point = new FinderPattern(centerJ, centerI, estimatedModuleSize); + possibleCenters.addElement(point); + if (resultPointCallback != null) { + resultPointCallback.foundPossibleResultPoint(point); + } } return true; } @@ -438,7 +459,7 @@ final class FinderPatternFinder { * at least {@link #CENTER_QUORUM} times each, and, the estimated module size of the * candidates is "pretty similar" */ - private boolean haveMulitplyConfirmedCenters() { + private boolean haveMultiplyConfirmedCenters() { int confirmedCount = 0; float totalModuleSize = 0.0f; int max = possibleCenters.size(); @@ -455,50 +476,69 @@ final 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. - float average = totalModuleSize / max; + // 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++) { FinderPattern pattern = (FinderPattern) possibleCenters.elementAt(i); totalDeviation += Math.abs(pattern.getEstimatedModuleSize() - average); } - return totalDeviation <= 0.15f * totalModuleSize; + return totalDeviation <= 0.05f * totalModuleSize; } /** * @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 - * @throws ReaderException if 3 such finder patterns do not exist + * @throws NotFoundException if 3 such finder patterns do not exist */ - private FinderPattern[] selectBestPatterns() throws ReaderException { - Collections.insertionSort(possibleCenters, new CenterComparator()); - int size = 0; - int max = possibleCenters.size(); - while (size < max) { - if (((FinderPattern) possibleCenters.elementAt(size)).getCount() < CENTER_QUORUM) { - break; - } - size++; - } + private FinderPattern[] selectBestPatterns() throws NotFoundException { - if (size < 3) { + int startSize = possibleCenters.size(); + if (startSize < 3) { // Couldn't find enough finder patterns - throw ReaderException.getInstance(); + 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 + float totalModuleSize = 0.0f; + float square = 0.0f; + for (int i = 0; i < startSize; i++) { + float size = ((FinderPattern) possibleCenters.elementAt(i)).getEstimatedModuleSize(); + totalModuleSize += size; + square += size * size; + } + float average = totalModuleSize / (float) startSize; + float stdDev = (float) Math.sqrt(square / startSize - average * average); + + Collections.insertionSort(possibleCenters, new FurthestFromAverageComparator(average)); + + float limit = Math.max(0.2f * average, stdDev); + + for (int i = 0; i < possibleCenters.size() && possibleCenters.size() > 3; i++) { + FinderPattern pattern = (FinderPattern) possibleCenters.elementAt(i); + if (Math.abs(pattern.getEstimatedModuleSize() - average) > limit) { + possibleCenters.removeElementAt(i); + i--; + } + } } - if (size > 3) { + if (possibleCenters.size() > 3) { // Throw away all but those first size candidate points we found. - possibleCenters.setSize(size); - // 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 < size; i++) { - averageModuleSize += ((FinderPattern) possibleCenters.elementAt(i)).getEstimatedModuleSize(); + + float totalModuleSize = 0.0f; + for (int i = 0; i < possibleCenters.size(); i++) { + totalModuleSize += ((FinderPattern) possibleCenters.elementAt(i)).getEstimatedModuleSize(); } - averageModuleSize /= (float) size; - // We don't have java.util.Collections in J2ME - Collections.insertionSort(possibleCenters, new ClosestToAverageComparator(averageModuleSize)); + + float average = totalModuleSize / (float) possibleCenters.size(); + + Collections.insertionSort(possibleCenters, new CenterComparator(average)); + + possibleCenters.setSize(3); } return new FinderPattern[]{ @@ -509,29 +549,36 @@ final class FinderPatternFinder { } /** - *Orders by {@link FinderPattern#getCount()}, descending.
+ *Orders by furthest from average
*/ - private static class CenterComparator implements Comparator { + private static class FurthestFromAverageComparator implements Comparator { + private final float average; + private FurthestFromAverageComparator(float f) { + average = f; + } public int compare(Object center1, Object center2) { - return ((FinderPattern) center2).getCount() - ((FinderPattern) center1).getCount(); + float dA = Math.abs(((FinderPattern) center2).getEstimatedModuleSize() - average); + float dB = Math.abs(((FinderPattern) center1).getEstimatedModuleSize() - average); + return dA < dB ? -1 : (dA == dB ? 0 : 1); } } /** - *Orders by variance from average module size, ascending.
+ *Orders by {@link FinderPattern#getCount()}, descending.
*/ - private static class ClosestToAverageComparator implements Comparator { - private final float averageModuleSize; - - private ClosestToAverageComparator(float averageModuleSize) { - this.averageModuleSize = averageModuleSize; + private static class CenterComparator implements Comparator { + private final float average; + private CenterComparator(float f) { + average = f; } - public int compare(Object center1, Object center2) { - return Math.abs(((FinderPattern) center1).getEstimatedModuleSize() - averageModuleSize) < - Math.abs(((FinderPattern) center2).getEstimatedModuleSize() - averageModuleSize) ? - -1 : - 1; + if (((FinderPattern) center2).getCount() == ((FinderPattern) center1).getCount()) { + float dA = Math.abs(((FinderPattern) center2).getEstimatedModuleSize() - average); + float dB = Math.abs(((FinderPattern) center1).getEstimatedModuleSize() - average); + return dA < dB ? 1 : (dA == dB ? 0 : -1); + } else { + return ((FinderPattern) center2).getCount() - ((FinderPattern) center1).getCount(); + } } }