/*
* 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.Collections;
import java.util.Comparator;
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;
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 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);
boolean pureBarcode = hints != null
&& hints.containsKey(DecodeHintType.PURE_BARCODE);
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
stateCount[0] = 0;
stateCount[1] = 0;
stateCount[2] = 0;
stateCount[3] = 0;
stateCount[4] = 0;
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, pureBarcode);
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 {
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;
stateCount[0] = 0;
stateCount[1] = 0;
stateCount[2] = 0;
stateCount[3] = 0;
stateCount[4] = 0;
} else { // No, shift counts back by two
stateCount[0] = stateCount[2];
stateCount[1] = stateCount[3];
stateCount[2] = stateCount[4];
stateCount[3] = 1;
stateCount[4] = 0;
currentState = 3;
}
} else {
stateCount[++currentState]++;
}
} else { // Counting white pixels
stateCount[currentState]++;
}
}
}
if (foundPatternCross(stateCount)) {
boolean confirmed = handlePossibleCenter(stateCount, i, maxJ,
pureBarcode);
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 (float) (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;
}
private int[] getCrossCheckStateCount() {
crossCheckStateCount[0] = 0;
crossCheckStateCount[1] = 0;
crossCheckStateCount[2] = 0;
crossCheckStateCount[3] = 0;
crossCheckStateCount[4] = 0;
return crossCheckStateCount;
}
/**
* 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 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
* @param originalStateCountTotal
* The original state count total.
* @return true if proportions are withing expected limits
*/
private boolean crossCheckDiagonal(int startI, int centerJ, int maxCount,
int originalStateCountTotal) {
int[] stateCount = getCrossCheckStateCount();
// Start counting up, left from center finding black center mass
int i = 0;
while (startI >= i && centerJ >= i
&& image.get(centerJ - i, startI - i)) {
stateCount[2]++;
i++;
}
if (startI < i || centerJ < i) {
return false;
}
// Continue up, left finding white space
while (startI >= i && centerJ >= i
&& !image.get(centerJ - i, startI - i)
&& stateCount[1] <= maxCount) {
stateCount[1]++;
i++;
}
// If already too many modules in this state or ran off the edge:
if (startI < i || centerJ < i || stateCount[1] > maxCount) {
return false;
}
// Continue up, left finding black border
while (startI >= i && centerJ >= i
&& image.get(centerJ - i, startI - i)
&& stateCount[0] <= maxCount) {
stateCount[0]++;
i++;
}
if (stateCount[0] > maxCount) {
return false;
}
int maxI = image.getHeight();
int maxJ = image.getWidth();
// Now also count down, right from center
i = 1;
while (startI + i < maxI && centerJ + i < maxJ
&& image.get(centerJ + i, startI + i)) {
stateCount[2]++;
i++;
}
// Ran off the edge?
if (startI + i >= maxI || centerJ + i >= maxJ) {
return false;
}
while (startI + i < maxI && centerJ + i < maxJ
&& !image.get(centerJ + i, startI + i)
&& stateCount[3] < maxCount) {
stateCount[3]++;
i++;
}
if (startI + i >= maxI || centerJ + i >= maxJ
|| stateCount[3] >= maxCount) {
return false;
}
while (startI + i < maxI && centerJ + i < maxJ
&& image.get(centerJ + i, startI + i)
&& stateCount[4] < maxCount) {
stateCount[4]++;
i++;
}
if (stateCount[4] >= maxCount) {
return false;
}
// If we found a finder-pattern-like section, but its size is more than
// 100% different than
// the original, assume it's a false positive
int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2]
+ stateCount[3] + stateCount[4];
return Math.abs(stateCountTotal - originalStateCountTotal) < 2 * originalStateCountTotal
&& foundPatternCross(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;
}
/**
* <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
* @param pureBarcode
* true if in "pure barcode" mode
* @return true if a finder pattern candidate was found this time
*/
protected final boolean handlePossibleCenter(int[] stateCount, int i,
int j, boolean pureBarcode) {
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)
&& (!pureBarcode || crossCheckDiagonal((int) centerI,
(int) centerJ, stateCount[2], stateCountTotal))) {
float estimatedModuleSize = (float) 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 / (float) max;
float totalDeviation = 0.0f;
for (FinderPattern pattern : possibleCenters) {
totalDeviation += Math.abs(pattern.getEstimatedModuleSize()
- average);
}
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 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();
}
// 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 (FinderPattern center : possibleCenters) {
float size = center.getEstimatedModuleSize();
totalModuleSize += size;
square += size * size;
}
float average = totalModuleSize / (float) startSize;
float stdDev = (float) Math.sqrt(square / startSize - average
* average);
Collections.sort(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 = possibleCenters.get(i);
if (Math.abs(pattern.getEstimatedModuleSize() - average) > limit) {
possibleCenters.remove(i);
i--;
}
}
}
if (possibleCenters.size() > 3) {
// Throw away all but those first size candidate points we found.
float totalModuleSize = 0.0f;
for (FinderPattern possibleCenter : possibleCenters) {
totalModuleSize += possibleCenter.getEstimatedModuleSize();
}
float average = totalModuleSize / (float) 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) {
float dA = Math.abs(center2.getEstimatedModuleSize() - average);
float dB = Math.abs(center1.getEstimatedModuleSize() - average);
return dA < dB ? -1 : dA == dB ? 0 : 1;
}
}
/**
* <p>
* Orders by {@link FinderPattern#getCount()}, descending.
* </p>
*/
private static final class CenterComparator implements
Comparator<FinderPattern>, Serializable {
private final float average;
private CenterComparator(float f) {
average = f;
}
@Override
public int compare(FinderPattern center1, FinderPattern center2) {
if (center2.getCount() == center1.getCount()) {
float dA = Math.abs(center2.getEstimatedModuleSize() - average);
float dB = Math.abs(center1.getEstimatedModuleSize() - average);
return dA < dB ? 1 : dA == dB ? 0 : -1;
} else {
return center2.getCount() - center1.getCount();
}
}
}
}