MultiFinderPatternFinder.java
/*
* Copyright 2009 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.multi.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 com.google.zxing.qrcode.detector.FinderPattern;
import com.google.zxing.qrcode.detector.FinderPatternFinder;
import com.google.zxing.qrcode.detector.FinderPatternInfo;
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.
*
* <p>In contrast to {@link FinderPatternFinder}, this class will return an array of all possible
* QR code locations in the image.</p>
*
* <p>Use the TRY_HARDER hint to ask for a more thorough detection.</p>
*
* @author Sean Owen
* @author Hannes Erven
*/
public final class MultiFinderPatternFinder extends FinderPatternFinder {
private static final FinderPatternInfo[] EMPTY_RESULT_ARRAY = new FinderPatternInfo[0];
private static final FinderPattern[] EMPTY_FP_ARRAY = new FinderPattern[0];
private static final FinderPattern[][] EMPTY_FP_2D_ARRAY = new FinderPattern[0][];
// TODO MIN_MODULE_COUNT and MAX_MODULE_COUNT would be great hints to ask the user for
// since it limits the number of regions to decode
// max. legal count of modules per QR code edge (177)
private static final float MAX_MODULE_COUNT_PER_EDGE = 180;
// min. legal count per modules per QR code edge (11)
private static final float MIN_MODULE_COUNT_PER_EDGE = 9;
/**
* More or less arbitrary cutoff point for determining if two finder patterns might belong
* to the same code if they differ less than DIFF_MODSIZE_CUTOFF_PERCENT percent in their
* estimated modules sizes.
*/
private static final float DIFF_MODSIZE_CUTOFF_PERCENT = 0.05f;
/**
* More or less arbitrary cutoff point for determining if two finder patterns might belong
* to the same code if they differ less than DIFF_MODSIZE_CUTOFF pixels/module in their
* estimated modules sizes.
*/
private static final float DIFF_MODSIZE_CUTOFF = 0.5f;
/**
* A comparator that orders FinderPatterns by their estimated module size.
*/
private static final class ModuleSizeComparator implements Comparator<FinderPattern>, Serializable {
@Override
public int compare(FinderPattern center1, FinderPattern center2) {
float value = center2.getEstimatedModuleSize() - center1.getEstimatedModuleSize();
return value < 0.0 ? -1 : value > 0.0 ? 1 : 0;
}
}
public MultiFinderPatternFinder(BitMatrix image, ResultPointCallback resultPointCallback) {
super(image, resultPointCallback);
}
/**
* @return the 3 best {@link FinderPattern}s from our list of candidates. The "best" are
* those that have been detected at least 2 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[][] selectMultipleBestPatterns() throws NotFoundException {
List<FinderPattern> possibleCenters = new ArrayList<>();
for (FinderPattern fp : getPossibleCenters()) {
if (fp.getCount() >= 2) {
possibleCenters.add(fp);
}
}
int size = possibleCenters.size();
if (size < 3) {
// Couldn't find enough finder patterns
throw NotFoundException.getNotFoundInstance();
}
/*
* Begin HE modifications to safely detect multiple codes of equal size
*/
if (size == 3) {
return new FinderPattern[][] { possibleCenters.toArray(EMPTY_FP_ARRAY) };
}
// Sort by estimated module size to speed up the upcoming checks
Collections.sort(possibleCenters, new ModuleSizeComparator());
/*
* Now lets start: build a list of tuples of three finder locations that
* - feature similar module sizes
* - are placed in a distance so the estimated module count is within the QR specification
* - have similar distance between upper left/right and left top/bottom finder patterns
* - form a triangle with 90�� angle (checked by comparing top right/bottom left distance
* with pythagoras)
*
* Note: we allow each point to be used for more than one code region: this might seem
* counterintuitive at first, but the performance penalty is not that big. At this point,
* we cannot make a good quality decision whether the three finders actually represent
* a QR code, or are just by chance laid out so it looks like there might be a QR code there.
* So, if the layout seems right, lets have the decoder try to decode.
*/
List<FinderPattern[]> results = new ArrayList<>(); // holder for the results
for (int i1 = 0; i1 < (size - 2); i1++) {
FinderPattern p1 = possibleCenters.get(i1);
if (p1 == null) {
continue;
}
for (int i2 = i1 + 1; i2 < (size - 1); i2++) {
FinderPattern p2 = possibleCenters.get(i2);
if (p2 == null) {
continue;
}
// Compare the expected module sizes; if they are really off, skip
float vModSize12 = (p1.getEstimatedModuleSize() - p2.getEstimatedModuleSize()) /
Math.min(p1.getEstimatedModuleSize(), p2.getEstimatedModuleSize());
float vModSize12A = Math.abs(p1.getEstimatedModuleSize() - p2.getEstimatedModuleSize());
if (vModSize12A > DIFF_MODSIZE_CUTOFF && vModSize12 >= DIFF_MODSIZE_CUTOFF_PERCENT) {
// break, since elements are ordered by the module size deviation there cannot be
// any more interesting elements for the given p1.
break;
}
for (int i3 = i2 + 1; i3 < size; i3++) {
FinderPattern p3 = possibleCenters.get(i3);
if (p3 == null) {
continue;
}
// Compare the expected module sizes; if they are really off, skip
float vModSize23 = (p2.getEstimatedModuleSize() - p3.getEstimatedModuleSize()) /
Math.min(p2.getEstimatedModuleSize(), p3.getEstimatedModuleSize());
float vModSize23A = Math.abs(p2.getEstimatedModuleSize() - p3.getEstimatedModuleSize());
if (vModSize23A > DIFF_MODSIZE_CUTOFF && vModSize23 >= DIFF_MODSIZE_CUTOFF_PERCENT) {
// break, since elements are ordered by the module size deviation there cannot be
// any more interesting elements for the given p1.
break;
}
FinderPattern[] test = {p1, p2, p3};
ResultPoint.orderBestPatterns(test);
// Calculate the distances: a = topleft-bottomleft, b=topleft-topright, c = diagonal
FinderPatternInfo info = new FinderPatternInfo(test);
float dA = ResultPoint.distance(info.getTopLeft(), info.getBottomLeft());
float dC = ResultPoint.distance(info.getTopRight(), info.getBottomLeft());
float dB = ResultPoint.distance(info.getTopLeft(), info.getTopRight());
// Check the sizes
float estimatedModuleCount = (dA + dB) / (p1.getEstimatedModuleSize() * 2.0f);
if (estimatedModuleCount > MAX_MODULE_COUNT_PER_EDGE ||
estimatedModuleCount < MIN_MODULE_COUNT_PER_EDGE) {
continue;
}
// Calculate the difference of the edge lengths in percent
float vABBC = Math.abs((dA - dB) / Math.min(dA, dB));
if (vABBC >= 0.1f) {
continue;
}
// Calculate the diagonal length by assuming a 90�� angle at topleft
float dCpy = (float) Math.sqrt((double) dA * dA + (double) dB * dB);
// Compare to the real distance in %
float vPyC = Math.abs((dC - dCpy) / Math.min(dC, dCpy));
if (vPyC >= 0.1f) {
continue;
}
// All tests passed!
results.add(test);
}
}
}
if (!results.isEmpty()) {
return results.toArray(EMPTY_FP_2D_ARRAY);
}
// Nothing found!
throw NotFoundException.getNotFoundInstance();
}
public FinderPatternInfo[] findMulti(Map<DecodeHintType,?> hints) throws NotFoundException {
boolean tryHarder = hints != null && hints.containsKey(DecodeHintType.TRY_HARDER);
BitMatrix image = getImage();
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;
}
int[] stateCount = new int[5];
for (int i = iSkip - 1; i < maxI; 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) && handlePossibleCenter(stateCount, i, j)) { // Yes
// 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]++;
}
}
} // for j=...
if (foundPatternCross(stateCount)) {
handlePossibleCenter(stateCount, i, maxJ);
}
} // for i=iSkip-1 ...
FinderPattern[][] patternInfo = selectMultipleBestPatterns();
List<FinderPatternInfo> result = new ArrayList<>();
for (FinderPattern[] pattern : patternInfo) {
ResultPoint.orderBestPatterns(pattern);
result.add(new FinderPatternInfo(pattern));
}
if (result.isEmpty()) {
return EMPTY_RESULT_ARRAY;
} else {
return result.toArray(EMPTY_RESULT_ARRAY);
}
}
}