2 * Copyright 2008 Google Inc.
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.oned;
19 import com.google.zxing.BlackPointEstimationMethod;
20 import com.google.zxing.DecodeHintType;
21 import com.google.zxing.MonochromeBitmapSource;
22 import com.google.zxing.ReaderException;
23 import com.google.zxing.Result;
24 import com.google.zxing.ResultMetadataType;
25 import com.google.zxing.common.BitArray;
27 import java.util.Hashtable;
30 * <p>Encapsulates functionality and implementation that is common to all families
31 * of one-dimensional barcodes.</p>
33 * @author dswitkin@google.com (Daniel Switkin)
34 * @author srowen@google.com (Sean Owen)
36 public abstract class AbstractOneDReader implements OneDReader {
38 public final Result decode(MonochromeBitmapSource image) throws ReaderException {
39 return decode(image, null);
42 public final Result decode(MonochromeBitmapSource image, Hashtable hints) throws ReaderException {
43 boolean tryHarder = hints != null && hints.containsKey(DecodeHintType.TRY_HARDER);
45 return doDecode(image, hints, tryHarder);
46 } catch (ReaderException re) {
47 if (tryHarder && image.isRotateSupported()) {
48 MonochromeBitmapSource rotatedImage = image.rotateCounterClockwise();
49 Result result = doDecode(rotatedImage, hints, tryHarder);
50 // Record that we found it rotated 90 degrees CCW / 270 degrees CW
51 Hashtable metadata = result.getResultMetadata();
52 int orientation = 270;
53 if (metadata != null && metadata.containsKey(ResultMetadataType.ORIENTATION)) {
54 // But if we found it reversed in doDecode(), add in that result here:
55 orientation = (orientation + ((Integer) metadata.get(ResultMetadataType.ORIENTATION)).intValue()) % 360;
57 result.putMetadata(ResultMetadataType.ORIENTATION, new Integer(orientation));
65 private Result doDecode(MonochromeBitmapSource image, Hashtable hints, boolean tryHarder) throws ReaderException {
67 int width = image.getWidth();
68 int height = image.getHeight();
70 BitArray row = new BitArray(width);
72 // We're going to examine rows from the middle outward, searching alternately above and below the middle,
73 // and farther out each time. rowStep is the number of rows between each successive attempt above and below
74 // the middle. So we'd scan row middle, then middle - rowStep, then middle + rowStep,
75 // then middle - 2*rowStep, etc.
76 // rowStep is bigger as the image is taller, but is always at least 1. We've somewhat arbitrarily decided
77 // that moving up and down by about 1/16 of the image is pretty good; we try more of the image if
79 int middle = height >> 1;
80 int rowStep = Math.max(1, height >> (tryHarder ? 7 : 4));
83 maxLines = height; // Look at the whole image; looking for more than one barcode
88 for (int x = 0; x < maxLines; x++) {
90 // Scanning from the middle out. Determine which row we're looking at next:
91 int rowStepsAboveOrBelow = (x + 1) >> 1;
92 boolean isAbove = (x & 0x01) == 0; // i.e. is x even?
93 int rowNumber = middle + rowStep * (isAbove ? rowStepsAboveOrBelow : -rowStepsAboveOrBelow);
94 if (rowNumber < 0 || rowNumber >= height) {
95 // Oops, if we run off the top or bottom, stop
99 // Estimate black point for this row and load it:
101 image.estimateBlackPoint(BlackPointEstimationMethod.ROW_SAMPLING, rowNumber);
102 } catch (ReaderException re) {
105 image.getBlackRow(rowNumber, row, 0, width);
107 // We may try twice for each row, if "trying harder":
108 for (int attempt = 0; attempt < 2; attempt++) {
109 if (attempt == 1) { // trying again?
110 if (tryHarder) { // only if "trying harder"
111 row.reverse(); // reverse the row and continue
117 // Look for a barcode
118 Result result = decodeRow(rowNumber, row, hints);
119 // We found our barcode
121 // But it was upside down, so note that
122 result.putMetadata(ResultMetadataType.ORIENTATION, new Integer(180));
125 } catch (ReaderException re) {
126 // continue -- just couldn't decode this row
131 throw new ReaderException("No barcode found");
135 * Records the size of successive runs of white and black pixels in a row, starting at a given point.
136 * The values are recorded in the given array, and the number of runs recorded is equal to the size
137 * of the array. If the row starts on a white pixel at the given start point, then the first count
138 * recorded is the run of white pixels starting from that point; likewise it is the count of a run
139 * of black pixels if the row begin on a black pixels at that point.
141 * @param row row to count from
142 * @param start offset into row to start at
143 * @param counters array into which to record counts
144 * @throws ReaderException if counters cannot be filled entirely from row before running out of pixels
146 static void recordPattern(BitArray row, int start, int[] counters) throws ReaderException {
147 int numCounters = counters.length;
148 for (int i = 0; i < numCounters; i++) {
151 int end = row.getSize();
153 throw new ReaderException("Couldn't fully read a pattern");
155 boolean isWhite = !row.get(start);
156 int counterPosition = 0;
159 boolean pixel = row.get(i);
160 if ((!pixel && isWhite) || (pixel && !isWhite)) {
161 counters[counterPosition]++;
164 if (counterPosition == numCounters) {
167 counters[counterPosition] = 1;
173 // If we read fully the last section of pixels and filled up our counters -- or filled
174 // the last counter but ran off the side of the image, OK. Otherwise, a problem.
175 if (!(counterPosition == numCounters || (counterPosition == numCounters - 1 && i == end))) {
176 throw new ReaderException("Couldn't fully read a pattern");
181 * Determines how closely a set of observed counts of runs of black/white values matches a given
182 * target pattern. This is reported as the ratio of the total variance from the expected pattern proportions
183 * across all pattern elements, to the length of the pattern.
185 * @param counters observed counters
186 * @param pattern expected pattern
187 * @return average variance between counters and pattern
189 static float patternMatchVariance(int[] counters, int[] pattern) {
191 int numCounters = counters.length;
192 int patternLength = 0;
193 for (int i = 0; i < numCounters; i++) {
194 total += counters[i];
195 patternLength += pattern[i];
197 float unitBarWidth = (float) total / (float) patternLength;
199 float totalVariance = 0.0f;
200 for (int x = 0; x < numCounters; x++) {
201 float scaledCounter = (float) counters[x] / unitBarWidth;
202 float width = pattern[x];
203 float abs = scaledCounter > width ? scaledCounter - width : width - scaledCounter;
204 totalVariance += abs;
206 return totalVariance / (float) patternLength;
209 // This declaration should not be necessary, since this class is
210 // abstract and so does not have to provide an implementation for every
211 // method of an interface it implements, but it is causing NoSuchMethodError
212 // issues on some Nokia JVMs. So we add this superfluous declaration:
214 public abstract Result decodeRow(int rowNumber, BitArray row, Hashtable hints) throws ReaderException;