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 private static final int INTEGER_MATH_SHIFT = 8;
40 public final Result decode(MonochromeBitmapSource image) throws ReaderException {
41 return decode(image, null);
44 public final Result decode(MonochromeBitmapSource image, Hashtable hints) throws ReaderException {
45 boolean tryHarder = hints != null && hints.containsKey(DecodeHintType.TRY_HARDER);
47 return doDecode(image, hints, tryHarder);
48 } catch (ReaderException re) {
49 if (tryHarder && image.isRotateSupported()) {
50 MonochromeBitmapSource rotatedImage = image.rotateCounterClockwise();
51 Result result = doDecode(rotatedImage, hints, tryHarder);
52 // Record that we found it rotated 90 degrees CCW / 270 degrees CW
53 Hashtable metadata = result.getResultMetadata();
54 int orientation = 270;
55 if (metadata != null && metadata.containsKey(ResultMetadataType.ORIENTATION)) {
56 // But if we found it reversed in doDecode(), add in that result here:
57 orientation = (orientation + ((Integer) metadata.get(ResultMetadataType.ORIENTATION)).intValue()) % 360;
59 result.putMetadata(ResultMetadataType.ORIENTATION, new Integer(orientation));
67 private Result doDecode(MonochromeBitmapSource image, Hashtable hints, boolean tryHarder) throws ReaderException {
69 int width = image.getWidth();
70 int height = image.getHeight();
72 BitArray row = new BitArray(width);
74 // We're going to examine rows from the middle outward, searching alternately above and below the middle,
75 // and farther out each time. rowStep is the number of rows between each successive attempt above and below
76 // the middle. So we'd scan row middle, then middle - rowStep, then middle + rowStep,
77 // then middle - 2*rowStep, etc.
78 // rowStep is bigger as the image is taller, but is always at least 1. We've somewhat arbitrarily decided
79 // that moving up and down by about 1/16 of the image is pretty good; we try more of the image if
81 int middle = height >> 1;
82 int rowStep = Math.max(1, height >> (tryHarder ? 7 : 4));
85 maxLines = height; // Look at the whole image; looking for more than one barcode
90 for (int x = 0; x < maxLines; x++) {
92 // Scanning from the middle out. Determine which row we're looking at next:
93 int rowStepsAboveOrBelow = (x + 1) >> 1;
94 boolean isAbove = (x & 0x01) == 0; // i.e. is x even?
95 int rowNumber = middle + rowStep * (isAbove ? rowStepsAboveOrBelow : -rowStepsAboveOrBelow);
96 if (rowNumber < 0 || rowNumber >= height) {
97 // Oops, if we run off the top or bottom, stop
101 // Estimate black point for this row and load it:
103 image.estimateBlackPoint(BlackPointEstimationMethod.ROW_SAMPLING, rowNumber);
104 } catch (ReaderException re) {
107 image.getBlackRow(rowNumber, row, 0, width);
109 // While we have the image data in a BitArray, it's fairly cheap to reverse it in place to
110 // handle decoding upside down barcodes.
111 for (int attempt = 0; attempt < 2; attempt++) {
112 if (attempt == 1) { // trying again?
113 row.reverse(); // reverse the row and continue
116 // Look for a barcode
117 Result result = decodeRow(rowNumber, row, hints);
118 // We found our barcode
120 // But it was upside down, so note that
121 result.putMetadata(ResultMetadataType.ORIENTATION, new Integer(180));
124 } catch (ReaderException re) {
125 // continue -- just couldn't decode this row
130 throw new ReaderException("No barcode found");
134 * Records the size of successive runs of white and black pixels in a row, starting at a given point.
135 * The values are recorded in the given array, and the number of runs recorded is equal to the size
136 * of the array. If the row starts on a white pixel at the given start point, then the first count
137 * recorded is the run of white pixels starting from that point; likewise it is the count of a run
138 * of black pixels if the row begin on a black pixels at that point.
140 * @param row row to count from
141 * @param start offset into row to start at
142 * @param counters array into which to record counts
143 * @throws ReaderException if counters cannot be filled entirely from row before running out of pixels
145 static void recordPattern(BitArray row, int start, int[] counters) throws ReaderException {
146 int numCounters = counters.length;
147 for (int i = 0; i < numCounters; i++) {
150 int end = row.getSize();
152 throw new ReaderException("Couldn't fully read a pattern");
154 boolean isWhite = !row.get(start);
155 int counterPosition = 0;
158 boolean pixel = row.get(i);
159 if ((!pixel && isWhite) || (pixel && !isWhite)) {
160 counters[counterPosition]++;
163 if (counterPosition == numCounters) {
166 counters[counterPosition] = 1;
172 // If we read fully the last section of pixels and filled up our counters -- or filled
173 // the last counter but ran off the side of the image, OK. Otherwise, a problem.
174 if (!(counterPosition == numCounters || (counterPosition == numCounters - 1 && i == end))) {
175 throw new ReaderException("Couldn't fully read a pattern");
180 * Determines how closely a set of observed counts of runs of black/white values matches a given
181 * target pattern. This is reported as the ratio of the total variance from the expected pattern proportions
182 * across all pattern elements, to the length of the pattern.
184 * @param counters observed counters
185 * @param pattern expected pattern
186 * @return ratio of total variance between counters and pattern compared to total pattern size,
187 * where the ratio has been multiplied by 256. So, 0 means no variance (perfect match); 256 means
188 * the total variance between counters and patterns equals the pattern length, higher values mean
191 static int patternMatchVariance(int[] counters, int[] pattern) {
192 int numCounters = counters.length;
194 int patternLength = 0;
195 for (int i = 0; i < numCounters; i++) {
196 total += counters[i];
197 patternLength += pattern[i];
199 if (total < patternLength) {
200 // If we don't even have one pixel per unit of bar width, assume this is too small
201 // to reliably match, so fail:
202 return Integer.MAX_VALUE;
204 // We're going to fake floating-point math in integers. We just need to use more bits.
205 // Scale up patternLength so that intermediate values below like scaledCounter will have
206 // more "significant digits"
207 patternLength <<= INTEGER_MATH_SHIFT;
208 int patternRatio = patternLength / total;
210 int totalVariance = 0;
211 for (int x = 0; x < numCounters; x++) {
212 int scaledCounter = counters[x] * patternRatio;
213 int width = pattern[x] << INTEGER_MATH_SHIFT;
214 totalVariance += scaledCounter > width ? scaledCounter - width : width - scaledCounter;
216 return (totalVariance << 8) / patternLength;
219 // This declaration should not be necessary, since this class is
220 // abstract and so does not have to provide an implementation for every
221 // method of an interface it implements, but it is causing NoSuchMethodError
222 // issues on some Nokia JVMs. So we add this superfluous declaration:
224 public abstract Result decodeRow(int rowNumber, BitArray row, Hashtable hints) throws ReaderException;