FinderPatternFinder.java
/*
* Copyright 2007 ZXing authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.zxing.qrcode.detector;
import com.google.zxing.DecodeHintType;
import com.google.zxing.NotFoundException;
import com.google.zxing.ResultPoint;
import com.google.zxing.ResultPointCallback;
import com.google.zxing.common.BitMatrix;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
/**
* <p>This class attempts to find finder patterns in a QR Code. Finder patterns are the square
* markers at three corners of a QR Code.</p>
*
* <p>This class is thread-safe but not reentrant. Each thread must allocate its own object.
*
* @author Sean Owen
*/
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
private final BitMatrix image;
private final List<FinderPattern> possibleCenters;
private boolean hasSkipped;
private final int[] crossCheckStateCount;
private final ResultPointCallback resultPointCallback;
/**
* <p>Creates a finder that will search the image for three finder patterns.</p>
*
* @param image image to search
*/
public FinderPatternFinder(BitMatrix image) {
this(image, null);
}
public FinderPatternFinder(BitMatrix image, ResultPointCallback resultPointCallback) {
this.image = image;
this.possibleCenters = new ArrayList<>();
this.crossCheckStateCount = new int[5];
this.resultPointCallback = resultPointCallback;
}
protected final BitMatrix getImage() {
return image;
}
protected final List<FinderPattern> getPossibleCenters() {
return possibleCenters;
}
final FinderPatternInfo find(Map<DecodeHintType,?> hints) throws NotFoundException {
boolean tryHarder = hints != null && hints.containsKey(DecodeHintType.TRY_HARDER);
int maxI = image.getHeight();
int maxJ = image.getWidth();
// We are looking for black/white/black/white/black modules in
// 1:1:3:1:1 ratio; this tracks the number of such modules seen so far
// Let's assume that the maximum version QR Code we support takes up 1/4 the height of the
// 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 = (3 * maxI) / (4 * MAX_MODULES);
if (iSkip < MIN_SKIP || tryHarder) {
iSkip = MIN_SKIP;
}
boolean done = false;
int[] stateCount = new int[5];
for (int i = iSkip - 1; i < maxI && !done; i += iSkip) {
// Get a row of black/white values
doClearCounts(stateCount);
int currentState = 0;
for (int j = 0; j < maxJ; j++) {
if (image.get(j, i)) {
// Black pixel
if ((currentState & 1) == 1) { // Counting white pixels
currentState++;
}
stateCount[currentState]++;
} else { // White pixel
if ((currentState & 1) == 0) { // Counting black pixels
if (currentState == 4) { // A winner?
if (foundPatternCross(stateCount)) { // Yes
boolean confirmed = handlePossibleCenter(stateCount, i, j);
if (confirmed) {
// Start examining every other line. Checking each line turned out to be too
// expensive and didn't improve performance.
iSkip = 2;
if (hasSkipped) {
done = haveMultiplyConfirmedCenters();
} else {
int rowSkip = findRowSkip();
if (rowSkip > stateCount[2]) {
// Skip rows between row of lower confirmed center
// and top of presumed third confirmed center
// but back up a bit to get a full chance of detecting
// it, entire width of center of finder pattern
// Skip by rowSkip, but back off by stateCount[2] (size of last center
// of pattern we saw) to be conservative, and also back off by iSkip which
// is about to be re-added
i += rowSkip - stateCount[2] - iSkip;
j = maxJ - 1;
}
}
} else {
doShiftCounts2(stateCount);
currentState = 3;
continue;
}
// Clear state to start looking again
currentState = 0;
doClearCounts(stateCount);
} else { // No, shift counts back by two
doShiftCounts2(stateCount);
currentState = 3;
}
} else {
stateCount[++currentState]++;
}
} else { // Counting white pixels
stateCount[currentState]++;
}
}
}
if (foundPatternCross(stateCount)) {
boolean confirmed = handlePossibleCenter(stateCount, i, maxJ);
if (confirmed) {
iSkip = stateCount[0];
if (hasSkipped) {
// Found a third one
done = haveMultiplyConfirmedCenters();
}
}
}
}
FinderPattern[] patternInfo = selectBestPatterns();
ResultPoint.orderBestPatterns(patternInfo);
return new FinderPatternInfo(patternInfo);
}
/**
* Given a count of black/white/black/white/black pixels just seen and an end position,
* figures the location of the center of this run.
*/
private static float centerFromEnd(int[] stateCount, int end) {
return (end - stateCount[4] - stateCount[3]) - stateCount[2] / 2.0f;
}
/**
* @param stateCount count of black/white/black/white/black pixels just read
* @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
*/
protected static boolean foundPatternCross(int[] stateCount) {
int totalModuleSize = 0;
for (int i = 0; i < 5; i++) {
int count = stateCount[i];
if (count == 0) {
return false;
}
totalModuleSize += count;
}
if (totalModuleSize < 7) {
return false;
}
float moduleSize = totalModuleSize / 7.0f;
float maxVariance = moduleSize / 2.0f;
// Allow less than 50% variance from 1-1-3-1-1 proportions
return
Math.abs(moduleSize - stateCount[0]) < maxVariance &&
Math.abs(moduleSize - stateCount[1]) < maxVariance &&
Math.abs(3.0f * moduleSize - stateCount[2]) < 3 * maxVariance &&
Math.abs(moduleSize - stateCount[3]) < maxVariance &&
Math.abs(moduleSize - stateCount[4]) < maxVariance;
}
/**
* @param stateCount count of black/white/black/white/black pixels just read
* @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
*/
protected static boolean foundPatternDiagonal(int[] stateCount) {
int totalModuleSize = 0;
for (int i = 0; i < 5; i++) {
int count = stateCount[i];
if (count == 0) {
return false;
}
totalModuleSize += count;
}
if (totalModuleSize < 7) {
return false;
}
float moduleSize = totalModuleSize / 7.0f;
float maxVariance = moduleSize / 1.333f;
// Allow less than 75% variance from 1-1-3-1-1 proportions
return
Math.abs(moduleSize - stateCount[0]) < maxVariance &&
Math.abs(moduleSize - stateCount[1]) < maxVariance &&
Math.abs(3.0f * moduleSize - stateCount[2]) < 3 * maxVariance &&
Math.abs(moduleSize - stateCount[3]) < maxVariance &&
Math.abs(moduleSize - stateCount[4]) < maxVariance;
}
private int[] getCrossCheckStateCount() {
doClearCounts(crossCheckStateCount);
return crossCheckStateCount;
}
@Deprecated
protected final void clearCounts(int[] counts) {
doClearCounts(counts);
}
@Deprecated
protected final void shiftCounts2(int[] stateCount) {
doShiftCounts2(stateCount);
}
protected static void doClearCounts(int[] counts) {
Arrays.fill(counts, 0);
}
protected static void doShiftCounts2(int[] stateCount) {
stateCount[0] = stateCount[2];
stateCount[1] = stateCount[3];
stateCount[2] = stateCount[4];
stateCount[3] = 1;
stateCount[4] = 0;
}
/**
* After a vertical and horizontal scan finds a potential finder pattern, this method
* "cross-cross-cross-checks" by scanning down diagonally through the center of the possible
* finder pattern to see if the same proportion is detected.
*
* @param centerI row where a finder pattern was detected
* @param centerJ center of the section that appears to cross a finder pattern
* @return true if proportions are withing expected limits
*/
private boolean crossCheckDiagonal(int centerI, int centerJ) {
int[] stateCount = getCrossCheckStateCount();
// Start counting up, left from center finding black center mass
int i = 0;
while (centerI >= i && centerJ >= i && image.get(centerJ - i, centerI - i)) {
stateCount[2]++;
i++;
}
if (stateCount[2] == 0) {
return false;
}
// Continue up, left finding white space
while (centerI >= i && centerJ >= i && !image.get(centerJ - i, centerI - i)) {
stateCount[1]++;
i++;
}
if (stateCount[1] == 0) {
return false;
}
// Continue up, left finding black border
while (centerI >= i && centerJ >= i && image.get(centerJ - i, centerI - i)) {
stateCount[0]++;
i++;
}
if (stateCount[0] == 0) {
return false;
}
int maxI = image.getHeight();
int maxJ = image.getWidth();
// Now also count down, right from center
i = 1;
while (centerI + i < maxI && centerJ + i < maxJ && image.get(centerJ + i, centerI + i)) {
stateCount[2]++;
i++;
}
while (centerI + i < maxI && centerJ + i < maxJ && !image.get(centerJ + i, centerI + i)) {
stateCount[3]++;
i++;
}
if (stateCount[3] == 0) {
return false;
}
while (centerI + i < maxI && centerJ + i < maxJ && image.get(centerJ + i, centerI + i)) {
stateCount[4]++;
i++;
}
if (stateCount[4] == 0) {
return false;
}
return foundPatternDiagonal(stateCount);
}
/**
* <p>After a horizontal scan finds a potential finder pattern, this method
* "cross-checks" by scanning down vertically through the center of the possible
* finder pattern to see if the same proportion is detected.</p>
*
* @param startI row where a finder pattern was detected
* @param centerJ center of the section that appears to cross a finder pattern
* @param maxCount maximum reasonable number of modules that should be
* 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) {
BitMatrix image = this.image;
int maxI = image.getHeight();
int[] stateCount = getCrossCheckStateCount();
// Start counting up from center
int i = startI;
while (i >= 0 && image.get(centerJ, i)) {
stateCount[2]++;
i--;
}
if (i < 0) {
return Float.NaN;
}
while (i >= 0 && !image.get(centerJ, i) && stateCount[1] <= maxCount) {
stateCount[1]++;
i--;
}
// If already too many modules in this state or ran off the edge:
if (i < 0 || stateCount[1] > maxCount) {
return Float.NaN;
}
while (i >= 0 && image.get(centerJ, i) && stateCount[0] <= maxCount) {
stateCount[0]++;
i--;
}
if (stateCount[0] > maxCount) {
return Float.NaN;
}
// Now also count down from center
i = startI + 1;
while (i < maxI && image.get(centerJ, i)) {
stateCount[2]++;
i++;
}
if (i == maxI) {
return Float.NaN;
}
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.get(centerJ, i) && stateCount[4] < maxCount) {
stateCount[4]++;
i++;
}
if (stateCount[4] >= maxCount) {
return Float.NaN;
}
// 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) >= 2 * originalStateCountTotal) {
return Float.NaN;
}
return foundPatternCross(stateCount) ? centerFromEnd(stateCount, i) : Float.NaN;
}
/**
* <p>Like {@link #crossCheckVertical(int, int, int, int)}, and in fact is basically identical,
* 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.</p>
*/
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.get(j, centerI)) {
stateCount[2]++;
j--;
}
if (j < 0) {
return Float.NaN;
}
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.get(j, centerI) && stateCount[0] <= maxCount) {
stateCount[0]++;
j--;
}
if (stateCount[0] > maxCount) {
return Float.NaN;
}
j = startJ + 1;
while (j < maxJ && image.get(j, centerI)) {
stateCount[2]++;
j++;
}
if (j == maxJ) {
return Float.NaN;
}
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.get(j, centerI) && stateCount[4] < maxCount) {
stateCount[4]++;
j++;
}
if (stateCount[4] >= maxCount) {
return Float.NaN;
}
// 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];
if (5 * Math.abs(stateCountTotal - originalStateCountTotal) >= originalStateCountTotal) {
return Float.NaN;
}
return foundPatternCross(stateCount) ? centerFromEnd(stateCount, j) : Float.NaN;
}
/**
* @param stateCount reading state module counts from horizontal scan
* @param i row where finder pattern may be found
* @param j end of possible finder pattern in row
* @param pureBarcode ignored
* @return true if a finder pattern candidate was found this time
* @deprecated only exists for backwards compatibility
* @see #handlePossibleCenter(int[], int, int)
*/
@Deprecated
protected final boolean handlePossibleCenter(int[] stateCount, int i, int j, boolean pureBarcode) {
return handlePossibleCenter(stateCount, i, j);
}
/**
* <p>This is called when a horizontal scan finds a possible alignment pattern. It will
* cross check with a vertical scan, and if successful, will, ah, cross-cross-check
* with another horizontal scan. This is needed primarily to locate the real horizontal
* center of the pattern in cases of extreme skew.
* And then we cross-cross-cross check with another diagonal scan.</p>
*
* <p>If that succeeds the finder pattern location is added to a list that tracks
* the number of times each location has been nearly-matched as a finder pattern.
* Each additional find is more evidence that the location is in fact a finder
* pattern center
*
* @param stateCount reading state module counts from horizontal scan
* @param i row where finder pattern may be found
* @param j end of possible finder pattern in row
* @return true if a finder pattern candidate was found this time
*/
protected final 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)) {
// Re-cross check
centerJ = crossCheckHorizontal((int) centerJ, (int) centerI, stateCount[2], stateCountTotal);
if (!Float.isNaN(centerJ) && crossCheckDiagonal((int) centerI, (int) centerJ)) {
float estimatedModuleSize = stateCountTotal / 7.0f;
boolean found = false;
for (int index = 0; index < possibleCenters.size(); index++) {
FinderPattern center = possibleCenters.get(index);
// Look for about the same center and module size:
if (center.aboutEquals(estimatedModuleSize, centerI, centerJ)) {
possibleCenters.set(index, center.combineEstimate(centerI, centerJ, estimatedModuleSize));
found = true;
break;
}
}
if (!found) {
FinderPattern point = new FinderPattern(centerJ, centerI, estimatedModuleSize);
possibleCenters.add(point);
if (resultPointCallback != null) {
resultPointCallback.foundPossibleResultPoint(point);
}
}
return true;
}
}
return false;
}
/**
* @return number of rows we could safely skip during scanning, based on the first
* two finder patterns that have been located. In some cases their position will
* allow us to infer that the third pattern must lie below a certain point farther
* down in the image.
*/
private int findRowSkip() {
int max = possibleCenters.size();
if (max <= 1) {
return 0;
}
ResultPoint firstConfirmedCenter = null;
for (FinderPattern center : possibleCenters) {
if (center.getCount() >= CENTER_QUORUM) {
if (firstConfirmedCenter == null) {
firstConfirmedCenter = center;
} else {
// We have two confirmed centers
// How far down can we skip before resuming looking for the next
// pattern? In the worst case, only the difference between the
// difference in the x / y coordinates of the two centers.
// This is the case where you find top left last.
hasSkipped = true;
return (int) (Math.abs(firstConfirmedCenter.getX() - center.getX()) -
Math.abs(firstConfirmedCenter.getY() - center.getY())) / 2;
}
}
}
return 0;
}
/**
* @return true iff we have found at least 3 finder patterns that have been detected
* at least {@link #CENTER_QUORUM} times each, and, the estimated module size of the
* candidates is "pretty similar"
*/
private boolean haveMultiplyConfirmedCenters() {
int confirmedCount = 0;
float totalModuleSize = 0.0f;
int max = possibleCenters.size();
for (FinderPattern pattern : possibleCenters) {
if (pattern.getCount() >= CENTER_QUORUM) {
confirmedCount++;
totalModuleSize += pattern.getEstimatedModuleSize();
}
}
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
// 5% of the total module size estimates, it's too much.
float average = totalModuleSize / max;
float totalDeviation = 0.0f;
for (FinderPattern pattern : possibleCenters) {
totalDeviation += Math.abs(pattern.getEstimatedModuleSize() - average);
}
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 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 {
int startSize = possibleCenters.size();
if (startSize < 3) {
// Couldn't find enough finder patterns
throw NotFoundException.getNotFoundInstance();
}
for (Iterator<FinderPattern> it = possibleCenters.iterator(); it.hasNext();) {
if (it.next().getCount() < CENTER_QUORUM) {
it.remove();
}
}
// A more up-to-date version would be "possibleCenters.sort(moduleComparator);"
// But we need this old syntax for android API 23 (Marshmallow) and below
// cf. https://github.com/zxing/zxing/issues/1358
Collections.sort(possibleCenters, moduleComparator);
double distortion = Double.MAX_VALUE;
FinderPattern[] bestPatterns = new FinderPattern[3];
for (int i = 0; i < possibleCenters.size() - 2; i++) {
FinderPattern fpi = possibleCenters.get(i);
float minModuleSize = fpi.getEstimatedModuleSize();
for (int j = i + 1; j < possibleCenters.size() - 1; j++) {
FinderPattern fpj = possibleCenters.get(j);
double squares0 = squaredDistance(fpi, fpj);
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;
}
double a = squares0;
double b = squaredDistance(fpj, fpk);
double c = squaredDistance(fpi, fpk);
// sorts ascending - inlined
if (a < b) {
if (b > c) {
if (a < c) {
double temp = b;
b = c;
c = temp;
} else {
double temp = a;
a = c;
c = b;
b = temp;
}
}
} else {
if (b < c) {
if (a < c) {
double temp = a;
a = b;
b = temp;
} else {
double temp = a;
a = b;
b = c;
c = temp;
}
} else {
double temp = a;
a = c;
c = temp;
}
}
// 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.
// Heuristically it seems that the following formula works better (although it's
// not clear any more why...)
double d = Math.abs(c - 2 * b) + Math.abs(c - 2 * a);
if (d < distortion) {
distortion = d;
bestPatterns[0] = fpi;
bestPatterns[1] = fpj;
bestPatterns[2] = fpk;
}
}
}
}
if (distortion == Double.MAX_VALUE) {
throw NotFoundException.getNotFoundInstance();
}
return bestPatterns;
}
/**
* <p>Orders by {@link FinderPattern#getEstimatedModuleSize()}</p>
*/
private static final class EstimatedModuleComparator implements Comparator<FinderPattern>, Serializable {
@Override
public int compare(FinderPattern center1, FinderPattern center2) {
return Float.compare(center1.getEstimatedModuleSize(), center2.getEstimatedModuleSize());
}
}
}