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.oned;
19 import com.google.zxing.BinaryBitmap;
20 import com.google.zxing.DecodeHintType;
21 import com.google.zxing.Reader;
22 import com.google.zxing.ReaderException;
23 import com.google.zxing.Result;
24 import com.google.zxing.ResultMetadataType;
25 import com.google.zxing.ResultPoint;
26 import com.google.zxing.common.BitArray;
28 import java.util.Enumeration;
29 import java.util.Hashtable;
32 * Encapsulates functionality and implementation that is common to all families
33 * of one-dimensional barcodes.
35 * @author dswitkin@google.com (Daniel Switkin)
38 public abstract class OneDReader implements Reader {
40 private static final int INTEGER_MATH_SHIFT = 8;
41 static final int PATTERN_MATCH_RESULT_SCALE_FACTOR = 1 << INTEGER_MATH_SHIFT;
43 public Result decode(BinaryBitmap image) throws ReaderException {
44 return decode(image, null);
47 // Note that we don't try rotation without the try harder flag, even if rotation was supported.
48 public Result decode(BinaryBitmap image, Hashtable hints) throws ReaderException {
50 return doDecode(image, hints);
51 } catch (ReaderException re) {
52 boolean tryHarder = hints != null && hints.containsKey(DecodeHintType.TRY_HARDER);
53 if (tryHarder && image.isRotateSupported()) {
54 BinaryBitmap rotatedImage = image.rotateCounterClockwise();
55 Result result = doDecode(rotatedImage, hints);
56 // Record that we found it rotated 90 degrees CCW / 270 degrees CW
57 Hashtable metadata = result.getResultMetadata();
58 int orientation = 270;
59 if (metadata != null && metadata.containsKey(ResultMetadataType.ORIENTATION)) {
60 // But if we found it reversed in doDecode(), add in that result here:
61 orientation = (orientation +
62 ((Integer) metadata.get(ResultMetadataType.ORIENTATION)).intValue()) % 360;
64 result.putMetadata(ResultMetadataType.ORIENTATION, new Integer(orientation));
73 * We're going to examine rows from the middle outward, searching alternately above and below the
74 * middle, and farther out each time. rowStep is the number of rows between each successive
75 * attempt above and below the middle. So we'd scan row middle, then middle - rowStep, then
76 * middle + rowStep, then middle - (2 * rowStep), etc.
77 * rowStep is bigger as the image is taller, but is always at least 1. We've somewhat arbitrarily
78 * decided that moving up and down by about 1/16 of the image is pretty good; we try more of the
79 * image if "trying harder".
81 * @param image The image to decode
82 * @param hints Any hints that were requested
83 * @return The contents of the decoded barcode
84 * @throws ReaderException Any spontaneous errors which occur
86 private Result doDecode(BinaryBitmap image, Hashtable hints) throws ReaderException {
87 int width = image.getWidth();
88 int height = image.getHeight();
89 BitArray row = new BitArray(width);
91 int middle = height >> 1;
92 boolean tryHarder = hints != null && hints.containsKey(DecodeHintType.TRY_HARDER);
93 int rowStep = Math.max(1, height >> (tryHarder ? 7 : 4));
96 maxLines = height; // Look at the whole image, not just the center
98 maxLines = 9; // Nine rows spaced 1/16 apart is roughly the middle half of the image
101 for (int x = 0; x < maxLines; x++) {
103 // Scanning from the middle out. Determine which row we're looking at next:
104 int rowStepsAboveOrBelow = (x + 1) >> 1;
105 boolean isAbove = (x & 0x01) == 0; // i.e. is x even?
106 int rowNumber = middle + rowStep * (isAbove ? rowStepsAboveOrBelow : -rowStepsAboveOrBelow);
107 if (rowNumber < 0 || rowNumber >= height) {
108 // Oops, if we run off the top or bottom, stop
112 // Estimate black point for this row and load it:
114 row = image.getBlackRow(rowNumber, row);
115 } catch (ReaderException re) {
119 // While we have the image data in a BitArray, it's fairly cheap to reverse it in place to
120 // handle decoding upside down barcodes.
121 for (int attempt = 0; attempt < 2; attempt++) {
122 if (attempt == 1) { // trying again?
123 row.reverse(); // reverse the row and continue
124 // This means we will only ever draw result points *once* in the life of this method
125 // since we want to avoid drawing the wrong points after flipping the row, and,
126 // don't want to clutter with noise from every single row scan -- just the scans
127 // that start on the center line.
128 if (hints != null && hints.containsKey(DecodeHintType.NEED_RESULT_POINT_CALLBACK)) {
129 Hashtable newHints = new Hashtable(); // Can't use clone() in J2ME
130 Enumeration hintEnum = hints.keys();
131 while (hintEnum.hasMoreElements()) {
132 Object key = hintEnum.nextElement();
133 if (!key.equals(DecodeHintType.NEED_RESULT_POINT_CALLBACK)) {
134 newHints.put(key, hints.get(key));
141 // Look for a barcode
142 Result result = decodeRow(rowNumber, row, hints);
143 // We found our barcode
145 // But it was upside down, so note that
146 result.putMetadata(ResultMetadataType.ORIENTATION, new Integer(180));
147 // And remember to flip the result points horizontally.
148 ResultPoint[] points = result.getResultPoints();
149 points[0] = new ResultPoint(width - points[0].getX() - 1, points[0].getY());
150 points[1] = new ResultPoint(width - points[1].getX() - 1, points[1].getY());
153 } catch (ReaderException re) {
154 // continue -- just couldn't decode this row
159 throw ReaderException.getInstance();
163 * Records the size of successive runs of white and black pixels in a row, starting at a given point.
164 * The values are recorded in the given array, and the number of runs recorded is equal to the size
165 * of the array. If the row starts on a white pixel at the given start point, then the first count
166 * recorded is the run of white pixels starting from that point; likewise it is the count of a run
167 * of black pixels if the row begin on a black pixels at that point.
169 * @param row row to count from
170 * @param start offset into row to start at
171 * @param counters array into which to record counts
172 * @throws ReaderException if counters cannot be filled entirely from row before running out
175 static void recordPattern(BitArray row, int start, int[] counters) throws ReaderException {
176 int numCounters = counters.length;
177 for (int i = 0; i < numCounters; i++) {
180 int end = row.getSize();
182 throw ReaderException.getInstance();
184 boolean isWhite = !row.get(start);
185 int counterPosition = 0;
188 boolean pixel = row.get(i);
189 if (pixel ^ isWhite) { // that is, exactly one is true
190 counters[counterPosition]++;
193 if (counterPosition == numCounters) {
196 counters[counterPosition] = 1;
197 isWhite ^= true; // isWhite = !isWhite;
202 // If we read fully the last section of pixels and filled up our counters -- or filled
203 // the last counter but ran off the side of the image, OK. Otherwise, a problem.
204 if (!(counterPosition == numCounters || (counterPosition == numCounters - 1 && i == end))) {
205 throw ReaderException.getInstance();
210 * Determines how closely a set of observed counts of runs of black/white values matches a given
211 * target pattern. This is reported as the ratio of the total variance from the expected pattern
212 * proportions across all pattern elements, to the length of the pattern.
214 * @param counters observed counters
215 * @param pattern expected pattern
216 * @param maxIndividualVariance The most any counter can differ before we give up
217 * @return ratio of total variance between counters and pattern compared to total pattern size,
218 * where the ratio has been multiplied by 256. So, 0 means no variance (perfect match); 256 means
219 * the total variance between counters and patterns equals the pattern length, higher values mean
222 static int patternMatchVariance(int[] counters, int[] pattern, int maxIndividualVariance) {
223 int numCounters = counters.length;
225 int patternLength = 0;
226 for (int i = 0; i < numCounters; i++) {
227 total += counters[i];
228 patternLength += pattern[i];
230 if (total < patternLength) {
231 // If we don't even have one pixel per unit of bar width, assume this is too small
232 // to reliably match, so fail:
233 return Integer.MAX_VALUE;
235 // We're going to fake floating-point math in integers. We just need to use more bits.
236 // Scale up patternLength so that intermediate values below like scaledCounter will have
237 // more "significant digits"
238 int unitBarWidth = (total << INTEGER_MATH_SHIFT) / patternLength;
239 maxIndividualVariance = (maxIndividualVariance * unitBarWidth) >> INTEGER_MATH_SHIFT;
241 int totalVariance = 0;
242 for (int x = 0; x < numCounters; x++) {
243 int counter = counters[x] << INTEGER_MATH_SHIFT;
244 int scaledPattern = pattern[x] * unitBarWidth;
245 int variance = counter > scaledPattern ? counter - scaledPattern : scaledPattern - counter;
246 if (variance > maxIndividualVariance) {
247 return Integer.MAX_VALUE;
249 totalVariance += variance;
251 return totalVariance / total;
255 * <p>Attempts to decode a one-dimensional barcode format given a single row of
258 * @param rowNumber row number from top of the row
259 * @param row the black/white pixel data of the row
260 * @param hints decode hints
261 * @return {@link Result} containing encoded string and start/end of barcode
262 * @throws ReaderException if an error occurs or barcode cannot be found
264 public abstract Result decodeRow(int rowNumber, BitArray row, Hashtable hints)
265 throws ReaderException;