2 * Copyright 2008 ZXing authors
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 package com.google.zxing.datamatrix.detector;
19 import com.google.zxing.NotFoundException;
20 import com.google.zxing.ResultPoint;
21 import com.google.zxing.common.BitMatrix;
22 import com.google.zxing.common.Collections;
23 import com.google.zxing.common.Comparator;
24 import com.google.zxing.common.DetectorResult;
25 import com.google.zxing.common.GridSampler;
26 import com.google.zxing.common.detector.WhiteRectangleDetector;
28 import java.util.Enumeration;
29 import java.util.Hashtable;
30 import java.util.Vector;
33 * <p>Encapsulates logic that can detect a Data Matrix Code in an image, even if the Data Matrix Code
34 * is rotated or skewed, or partially obscured.</p>
38 public final class Detector {
40 // Trick to avoid creating new Integer objects below -- a sort of crude copy of
41 // the Integer.valueOf(int) optimization added in Java 5, not in J2ME
42 private static final Integer[] INTEGERS =
43 { new Integer(0), new Integer(1), new Integer(2), new Integer(3), new Integer(4) };
44 // No, can't use valueOf()
46 private final BitMatrix image;
47 private final WhiteRectangleDetector rectangleDetector;
49 public Detector(BitMatrix image) {
51 rectangleDetector = new WhiteRectangleDetector(image);
55 * <p>Detects a Data Matrix Code in an image.</p>
57 * @return {@link DetectorResult} encapsulating results of detecting a Data Matrix Code
58 * @throws NotFoundException if no Data Matrix Code can be found
60 public DetectorResult detect() throws NotFoundException {
62 ResultPoint[] cornerPoints = rectangleDetector.detect();
63 ResultPoint pointA = cornerPoints[0];
64 ResultPoint pointB = cornerPoints[1];
65 ResultPoint pointC = cornerPoints[2];
66 ResultPoint pointD = cornerPoints[3];
68 // Point A and D are across the diagonal from one another,
69 // as are B and C. Figure out which are the solid black lines
70 // by counting transitions
71 Vector transitions = new Vector(4);
72 transitions.addElement(transitionsBetween(pointA, pointB));
73 transitions.addElement(transitionsBetween(pointA, pointC));
74 transitions.addElement(transitionsBetween(pointB, pointD));
75 transitions.addElement(transitionsBetween(pointC, pointD));
76 Collections.insertionSort(transitions, new ResultPointsAndTransitionsComparator());
78 // Sort by number of transitions. First two will be the two solid sides; last two
79 // will be the two alternating black/white sides
80 ResultPointsAndTransitions lSideOne = (ResultPointsAndTransitions) transitions.elementAt(0);
81 ResultPointsAndTransitions lSideTwo = (ResultPointsAndTransitions) transitions.elementAt(1);
83 // Figure out which point is their intersection by tallying up the number of times we see the
84 // endpoints in the four endpoints. One will show up twice.
85 Hashtable pointCount = new Hashtable();
86 increment(pointCount, lSideOne.getFrom());
87 increment(pointCount, lSideOne.getTo());
88 increment(pointCount, lSideTwo.getFrom());
89 increment(pointCount, lSideTwo.getTo());
91 ResultPoint maybeTopLeft = null;
92 ResultPoint bottomLeft = null;
93 ResultPoint maybeBottomRight = null;
94 Enumeration points = pointCount.keys();
95 while (points.hasMoreElements()) {
96 ResultPoint point = (ResultPoint) points.nextElement();
97 Integer value = (Integer) pointCount.get(point);
98 if (value.intValue() == 2) {
99 bottomLeft = point; // this is definitely the bottom left, then -- end of two L sides
101 // Otherwise it's either top left or bottom right -- just assign the two arbitrarily now
102 if (maybeTopLeft == null) {
103 maybeTopLeft = point;
105 maybeBottomRight = point;
110 if (maybeTopLeft == null || bottomLeft == null || maybeBottomRight == null) {
111 throw NotFoundException.getNotFoundInstance();
114 // Bottom left is correct but top left and bottom right might be switched
115 ResultPoint[] corners = { maybeTopLeft, bottomLeft, maybeBottomRight };
116 // Use the dot product trick to sort them out
117 ResultPoint.orderBestPatterns(corners);
119 // Now we know which is which:
120 ResultPoint bottomRight = corners[0];
121 bottomLeft = corners[1];
122 ResultPoint topLeft = corners[2];
124 // Which point didn't we find in relation to the "L" sides? that's the top right corner
125 ResultPoint topRight;
126 if (!pointCount.containsKey(pointA)) {
128 } else if (!pointCount.containsKey(pointB)) {
130 } else if (!pointCount.containsKey(pointC)) {
136 // Next determine the dimension by tracing along the top or right side and counting black/white
137 // transitions. Since we start inside a black module, we should see a number of transitions
138 // equal to 1 less than the code dimension. Well, actually 2 less, because we are going to
139 // end on a black module:
141 // The top right point is actually the corner of a module, which is one of the two black modules
142 // adjacent to the white module at the top right. Tracing to that corner from either the top left
143 // or bottom right should work here.
144 int dimension = Math.min(transitionsBetween(topLeft, topRight).getTransitions(),
145 transitionsBetween(bottomRight, topRight).getTransitions());
146 if ((dimension & 0x01) == 1) {
147 // it can't be odd, so, round... up?
152 //correct top right point to match the white module
153 ResultPoint correctedTopRight = correctTopRight(bottomLeft, bottomRight, topLeft, topRight, dimension);
155 //We redetermine the dimension using the corrected top right point
156 int dimension2 = Math.max(transitionsBetween(topLeft, correctedTopRight).getTransitions(),
157 transitionsBetween(bottomRight, correctedTopRight).getTransitions());
159 if ((dimension2 & 0x01) == 1) {
163 BitMatrix bits = sampleGrid(image, topLeft, bottomLeft, bottomRight, correctedTopRight, dimension2);
165 return new DetectorResult(bits, new ResultPoint[]{topLeft, bottomLeft, bottomRight, correctedTopRight});
169 * Calculates the position of the white top right module using the output of the rectangle detector
171 private ResultPoint correctTopRight(ResultPoint bottomLeft,
172 ResultPoint bottomRight,
174 ResultPoint topRight,
177 float corr = distance(bottomLeft, bottomRight) / (float)dimension;
178 int norm = distance(topLeft, topRight);
179 float cos = (topRight.getX() - topLeft.getX()) / norm;
180 float sin = (topRight.getY() - topLeft.getY()) / norm;
182 ResultPoint c1 = new ResultPoint(topRight.getX()+corr*cos, topRight.getY()+corr*sin);
184 corr = distance(bottomLeft, bottomRight) / (float)dimension;
185 norm = distance(bottomRight, topRight);
186 cos = (topRight.getX() - bottomRight.getX()) / norm;
187 sin = (topRight.getY() - bottomRight.getY()) / norm;
189 ResultPoint c2 = new ResultPoint(topRight.getX()+corr*cos, topRight.getY()+corr*sin);
191 int l1 = Math.abs(transitionsBetween(topLeft, c1).getTransitions() - transitionsBetween(bottomRight, c1).getTransitions());
192 int l2 = Math.abs(transitionsBetween(topLeft, c2).getTransitions() - transitionsBetween(bottomRight, c2).getTransitions());
202 private static int distance(ResultPoint a, ResultPoint b) {
203 return (int) Math.round(Math.sqrt((a.getX() - b.getX())
204 * (a.getX() - b.getX()) + (a.getY() - b.getY())
205 * (a.getY() - b.getY())));
209 * Increments the Integer associated with a key by one.
211 private static void increment(Hashtable table, ResultPoint key) {
212 Integer value = (Integer) table.get(key);
213 table.put(key, value == null ? INTEGERS[1] : INTEGERS[value.intValue() + 1]);
216 private static BitMatrix sampleGrid(BitMatrix image,
218 ResultPoint bottomLeft,
219 ResultPoint bottomRight,
220 ResultPoint topRight,
221 int dimension) throws NotFoundException {
223 GridSampler sampler = GridSampler.getInstance();
225 return sampler.sampleGrid(image,
246 * Counts the number of black/white transitions between two points, using something like Bresenham's algorithm.
248 private ResultPointsAndTransitions transitionsBetween(ResultPoint from, ResultPoint to) {
249 // See QR Code Detector, sizeOfBlackWhiteBlackRun()
250 int fromX = (int) from.getX();
251 int fromY = (int) from.getY();
252 int toX = (int) to.getX();
253 int toY = (int) to.getY();
254 boolean steep = Math.abs(toY - fromY) > Math.abs(toX - fromX);
264 int dx = Math.abs(toX - fromX);
265 int dy = Math.abs(toY - fromY);
266 int error = -dx >> 1;
267 int ystep = fromY < toY ? 1 : -1;
268 int xstep = fromX < toX ? 1 : -1;
270 boolean inBlack = image.get(steep ? fromY : fromX, steep ? fromX : fromY);
271 for (int x = fromX, y = fromY; x != toX; x += xstep) {
272 boolean isBlack = image.get(steep ? y : x, steep ? x : y);
273 if (isBlack != inBlack) {
286 return new ResultPointsAndTransitions(from, to, transitions);
290 * Simply encapsulates two points and a number of transitions between them.
292 private static class ResultPointsAndTransitions {
293 private final ResultPoint from;
294 private final ResultPoint to;
295 private final int transitions;
296 private ResultPointsAndTransitions(ResultPoint from, ResultPoint to, int transitions) {
299 this.transitions = transitions;
301 public ResultPoint getFrom() {
304 public ResultPoint getTo() {
307 public int getTransitions() {
310 public String toString() {
311 return from + "/" + to + '/' + transitions;
316 * Orders ResultPointsAndTransitions by number of transitions, ascending.
318 private static class ResultPointsAndTransitionsComparator implements Comparator {
319 public int compare(Object o1, Object o2) {
320 return ((ResultPointsAndTransitions) o1).getTransitions() - ((ResultPointsAndTransitions) o2).getTransitions();