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.MonochromeBitmapSource;
20 import com.google.zxing.ReaderException;
21 import com.google.zxing.ResultPoint;
22 import com.google.zxing.BlackPointEstimationMethod;
23 import com.google.zxing.common.BitMatrix;
24 import com.google.zxing.common.Collections;
25 import com.google.zxing.common.Comparator;
26 import com.google.zxing.common.DetectorResult;
27 import com.google.zxing.common.GenericResultPoint;
28 import com.google.zxing.common.GridSampler;
30 import java.util.Enumeration;
31 import java.util.Hashtable;
32 import java.util.Vector;
35 * <p>Encapsulates logic that can detect a Data Matrix Code in an image, even if the Data Matrix Code
36 * is rotated or skewed, or partially obscured.</p>
38 * @author srowen@google.com (Sean Owen)
40 public final class Detector {
42 private static final int MAX_MODULES = 32;
44 // Trick to avoid creating new Integer objects below -- a sort of crude copy of
45 // the Integer.valueOf(int) optimization added in Java 5, not in J2ME
46 private static final Integer[] INTEGERS =
47 { new Integer(0), new Integer(1), new Integer(2), new Integer(3), new Integer(4) };
49 private final MonochromeBitmapSource image;
51 public Detector(MonochromeBitmapSource image) {
56 * <p>Detects a Data Matrix Code in an image.</p>
58 * @return {@link DetectorResult} encapsulating results of detecting a QR Code
59 * @throws ReaderException if no Data Matrix Code can be found
61 public DetectorResult detect() throws ReaderException {
63 if (!BlackPointEstimationMethod.TWO_D_SAMPLING.equals(image.getLastEstimationMethod())) {
64 image.estimateBlackPoint(BlackPointEstimationMethod.TWO_D_SAMPLING, 0);
67 int height = image.getHeight();
68 int width = image.getWidth();
69 int halfHeight = height >> 1;
70 int halfWidth = width >> 1;
71 int iSkip = Math.max(1, height / (MAX_MODULES << 2));
72 int jSkip = Math.max(1, width / (MAX_MODULES << 2));
78 ResultPoint pointA = findCornerFromCenter(halfHeight, -iSkip, minI, maxI, halfWidth, 0, minJ, maxJ, halfWidth >> 2);
79 minI = (int) pointA.getY() - 1;
80 ResultPoint pointB = findCornerFromCenter(halfHeight, 0, minI, maxI, halfWidth, -jSkip, minJ, maxJ, halfHeight >> 2);
81 minJ = (int) pointB.getX() - 1;
82 ResultPoint pointC = findCornerFromCenter(halfHeight, 0, minI, maxI, halfWidth, jSkip, minJ, maxJ, halfHeight >> 2);
83 maxJ = (int) pointC.getX() + 1;
84 ResultPoint pointD = findCornerFromCenter(halfHeight, iSkip, minI, maxI, halfWidth, 0, minJ, maxJ, halfWidth >> 2);
85 maxI = (int) pointD.getY() + 1;
86 // Go try to find point A again with better information -- might have been off at first.
87 pointA = findCornerFromCenter(halfHeight, -iSkip, minI, maxI, halfWidth, 0, minJ, maxJ, halfWidth >> 2);
89 // Point A and D are across the diagonal from one another,
90 // as are B and C. Figure out which are the solid black lines
91 // by counting transitions
92 Vector transitions = new Vector(4);
93 transitions.addElement(transitionsBetween(pointA, pointB));
94 transitions.addElement(transitionsBetween(pointA, pointC));
95 transitions.addElement(transitionsBetween(pointB, pointD));
96 transitions.addElement(transitionsBetween(pointC, pointD));
97 Collections.insertionSort(transitions, new ResultPointsAndTransitionsComparator());
99 // Sort by number of transitions. First two will be the two solid sides; last two
100 // will be the two alternating black/white sides
101 ResultPointsAndTransitions lSideOne = (ResultPointsAndTransitions) transitions.elementAt(0);
102 ResultPointsAndTransitions lSideTwo = (ResultPointsAndTransitions) transitions.elementAt(1);
104 // Figure out which point is their intersection by tallying up the number of times we see the
105 // endpoints in the four endpoints. One will show up twice.
106 Hashtable pointCount = new Hashtable();
107 increment(pointCount, lSideOne.getFrom());
108 increment(pointCount, lSideOne.getTo());
109 increment(pointCount, lSideTwo.getFrom());
110 increment(pointCount, lSideTwo.getTo());
112 ResultPoint maybeTopLeft = null;
113 ResultPoint bottomLeft = null;
114 ResultPoint maybeBottomRight = null;
115 Enumeration points = pointCount.keys();
116 while (points.hasMoreElements()) {
117 ResultPoint point = (ResultPoint) points.nextElement();
118 Integer value = (Integer) pointCount.get(point);
119 if (value.intValue() == 2) {
120 bottomLeft = point; // this is definitely the bottom left, then -- end of two L sides
122 // Otherwise it's either top left or bottom right -- just assign the two arbitrarily now
123 if (maybeTopLeft == null) {
124 maybeTopLeft = point;
126 maybeBottomRight = point;
131 // Bottom left is correct but top left and bottom right might be switched
132 ResultPoint[] corners = new ResultPoint[] { maybeTopLeft, bottomLeft, maybeBottomRight };
133 // Use the dot product trick to sort them out
134 GenericResultPoint.orderBestPatterns(corners);
136 // Now we know which is which:
137 ResultPoint bottomRight = corners[0];
138 bottomLeft = corners[1];
139 ResultPoint topLeft = corners[2];
141 // Which point didn't we find in relation to the "L" sides? that's the top right corner
142 ResultPoint topRight;
143 if (!pointCount.containsKey(pointA)) {
145 } else if (!pointCount.containsKey(pointB)) {
147 } else if (!pointCount.containsKey(pointC)) {
153 // Next determine the dimension by tracing along the top or right side and counting black/white
154 // transitions. Since we start inside a black module, we should see a number of transitions
155 // equal to 1 less than the code dimension. Well, actually 2 less, because we are going to
156 // end on a black module:
158 // The top right point is actually the corner of a module, which is one of the two black modules
159 // adjacent to the white module at the top right. Tracing to that corner from either the top left
160 // or bottom right should work here, but, one will be more reliable since it's traced straight
161 // up or across, rather than at a slight angle. We use dot products to figure out which is
164 if (GenericResultPoint.crossProductZ(bottomLeft, bottomRight, topRight) <
165 GenericResultPoint.crossProductZ(topRight, topLeft, bottomLeft)) {
166 dimension = transitionsBetween(topLeft, topRight).getTransitions();
168 dimension = transitionsBetween(bottomRight, topRight).getTransitions();
172 BitMatrix bits = sampleGrid(image, topLeft, bottomLeft, bottomRight, dimension);
173 return new DetectorResult(bits, new ResultPoint[] {pointA, pointB, pointC, pointD});
177 * Attempts to locate a corner of the barcode by scanning up, down, left or right from a center
178 * point which should be within the barcode.
180 * @param centerI center's i componennt (vertical)
181 * @param di change in i per step. If scanning up this is negative; down, positive; left or right, 0
182 * @param minI minimum value of i to search through (meaningless when di == 0)
183 * @param maxI maximum value of i
184 * @param centerJ center's j component (horizontal)
185 * @param dj same as di but change in j per step instead
186 * @param minJ see minI
187 * @param maxJ see minJ
188 * @param maxWhiteRun maximum run of white pixels that can still be considered to be within
190 * @return a {@link ResultPoint} encapsulating the corner that was found
191 * @throws ReaderException if such a point cannot be found
193 private ResultPoint findCornerFromCenter(int centerI, int di, int minI, int maxI,
194 int centerJ, int dj, int minJ, int maxJ,
195 int maxWhiteRun) throws ReaderException {
196 int[] lastRange = null;
197 for (int i = centerI, j = centerJ;
198 i < maxI && i >= minI && j < maxJ && j >= minJ;
202 // horizontal slices, up and down
203 range = blackWhiteRange(i, maxWhiteRun, minJ, maxJ, true);
205 // vertical slices, left and right
206 range = blackWhiteRange(j, maxWhiteRun, minI, maxI, false);
209 if (lastRange == null) {
210 throw new ReaderException("Center of image not within barcode");
212 // lastRange was found
215 if (lastRange[0] < centerJ) {
216 if (lastRange[1] > centerJ) {
217 // straddle, choose one or the other based on direction
218 return new GenericResultPoint(di > 0 ? lastRange[0] : lastRange[1], lastI);
220 return new GenericResultPoint(lastRange[0], lastI);
222 return new GenericResultPoint(lastRange[1], lastI);
226 if (lastRange[0] < centerI) {
227 if (lastRange[1] > centerI) {
228 return new GenericResultPoint(lastJ, dj < 0 ? lastRange[0] : lastRange[1]);
230 return new GenericResultPoint(lastJ, lastRange[0]);
232 return new GenericResultPoint(lastJ, lastRange[1]);
238 throw new ReaderException("Couldn't find an end to barcode");
242 * Increments the Integer associated with a key by one.
244 private static void increment(Hashtable table, ResultPoint key) {
245 Integer value = (Integer) table.get(key);
246 table.put(key, value == null ? INTEGERS[1] : INTEGERS[value.intValue() + 1]);
250 * Computes the start and end of a region of pixels, either horizontally or vertically, that could be
251 * part of a Data Matrix barcode.
253 * @param fixedDimension if scanning horizontally, this is the row (the fixed vertical location) where
254 * we are scanning. If scanning vertically it's the colummn, the fixed horizontal location
255 * @param maxWhiteRun largest run of white pixels that can still be considered part of the barcode region
256 * @param minDim minimum pixel location, horizontally or vertically, to consider
257 * @param maxDim maximum pixel location, horizontally or vertically, to consider
258 * @param horizontal if true, we're scanning left-right, instead of up-down
259 * @return int[] with start and end of found range, or null if no such range is found (e.g. only white was found)
261 private int[] blackWhiteRange(int fixedDimension, int maxWhiteRun, int minDim, int maxDim, boolean horizontal) {
263 int center = (minDim + maxDim) / 2;
265 // Scan left/up first
267 while (start >= minDim) {
268 if (horizontal ? image.isBlack(start, fixedDimension) : image.isBlack(fixedDimension, start)) {
271 int whiteRunStart = start;
274 } while (start >= minDim &&
275 !(horizontal ? image.isBlack(start, fixedDimension) : image.isBlack(fixedDimension, start)));
276 int whiteRunSize = whiteRunStart - start;
277 if (start < minDim || whiteRunSize > maxWhiteRun) {
278 start = whiteRunStart + 1; // back up
284 // Then try right/down
286 while (end < maxDim) {
287 if (horizontal ? image.isBlack(end, fixedDimension) : image.isBlack(fixedDimension, end)) {
290 int whiteRunStart = end;
293 } while (end < maxDim &&
294 !(horizontal ? image.isBlack(end, fixedDimension) : image.isBlack(fixedDimension, end)));
295 int whiteRunSize = end - whiteRunStart;
296 if (end >= maxDim || whiteRunSize > maxWhiteRun) {
297 end = whiteRunStart - 1;
304 return new int[] { start, end };
310 private static BitMatrix sampleGrid(MonochromeBitmapSource image,
312 ResultPoint bottomLeft,
313 ResultPoint bottomRight,
314 int dimension) throws ReaderException {
316 // We make up the top right point for now, based on the others.
317 // TODO: we actually found a fourth corner above and figured out which of two modules
318 // it was the corner of. We could use that here and adjust for perspective distortion.
319 float topRightX = (bottomRight.getX() - bottomLeft.getX()) + topLeft.getX();
320 float topRightY = (bottomRight.getY() - bottomLeft.getY()) + topLeft.getY();
322 // Note that unlike in the QR Code sampler, we didn't find the center of modules, but the
323 // very corners. So there is no 0.5f here; 0.0f is right.
324 GridSampler sampler = GridSampler.getInstance();
325 return sampler.sampleGrid(
347 * Counts the number of black/white transitions between two points, using something like Bresenham's algorithm.
349 private ResultPointsAndTransitions transitionsBetween(ResultPoint from, ResultPoint to) {
350 // See QR Code Detector, sizeOfBlackWhiteBlackRun()
351 int fromX = (int) from.getX();
352 int fromY = (int) from.getY();
353 int toX = (int) to.getX();
354 int toY = (int) to.getY();
355 boolean steep = Math.abs(toY - fromY) > Math.abs(toX - fromX);
365 int dx = Math.abs(toX - fromX);
366 int dy = Math.abs(toY - fromY);
367 int error = -dx >> 1;
368 int ystep = fromY < toY ? 1 : -1;
369 int xstep = fromX < toX ? 1 : -1;
371 boolean inBlack = image.isBlack(steep ? fromY : fromX, steep ? fromX : fromY);
372 for (int x = fromX, y = fromY; x != toX; x += xstep) {
373 boolean isBlack = image.isBlack(steep ? y : x, steep ? x : y);
374 if (isBlack == !inBlack) {
384 return new ResultPointsAndTransitions(from, to, transitions);
388 * Simply encapsulates two points and a number of transitions between them.
390 private static class ResultPointsAndTransitions {
391 private final ResultPoint from;
392 private final ResultPoint to;
393 private final int transitions;
394 private ResultPointsAndTransitions(ResultPoint from, ResultPoint to, int transitions) {
397 this.transitions = transitions;
399 public ResultPoint getFrom() {
402 public ResultPoint getTo() {
405 public int getTransitions() {
408 public String toString() {
409 return from + "/" + to + '/' + transitions;
414 * Orders ResultPointsAndTransitions by number of transitions, ascending.
416 private static class ResultPointsAndTransitionsComparator implements Comparator {
417 public int compare(Object o1, Object o2) {
418 return ((ResultPointsAndTransitions) o1).getTransitions() - ((ResultPointsAndTransitions) o2).getTransitions();