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.ReaderException;
20 import com.google.zxing.Result;
21 import com.google.zxing.ResultPointCallback;
22 import com.google.zxing.DecodeHintType;
23 import com.google.zxing.ResultPoint;
24 import com.google.zxing.BarcodeFormat;
25 import com.google.zxing.common.BitArray;
27 import java.util.Hashtable;
30 * <p>Encapsulates functionality and implementation that is common to UPC and EAN families
31 * of one-dimensional barcodes.</p>
33 * @author dswitkin@google.com (Daniel Switkin)
35 * @author alasdair@google.com (Alasdair Mackintosh)
37 public abstract class UPCEANReader extends OneDReader {
39 // These two values are critical for determining how permissive the decoding will be.
40 // We've arrived at these values through a lot of trial and error. Setting them any higher
41 // lets false positives creep in quickly.
42 private static final int MAX_AVG_VARIANCE = (int) (PATTERN_MATCH_RESULT_SCALE_FACTOR * 0.42f);
43 private static final int MAX_INDIVIDUAL_VARIANCE = (int) (PATTERN_MATCH_RESULT_SCALE_FACTOR * 0.7f);
46 * Start/end guard pattern.
48 static final int[] START_END_PATTERN = {1, 1, 1,};
51 * Pattern marking the middle of a UPC/EAN pattern, separating the two halves.
53 static final int[] MIDDLE_PATTERN = {1, 1, 1, 1, 1};
56 * "Odd", or "L" patterns used to encode UPC/EAN digits.
58 static final int[][] L_PATTERNS = {
72 * As above but also including the "even", or "G" patterns used to encode UPC/EAN digits.
74 static final int[][] L_AND_G_PATTERNS;
77 L_AND_G_PATTERNS = new int[20][];
78 for (int i = 0; i < 10; i++) {
79 L_AND_G_PATTERNS[i] = L_PATTERNS[i];
81 for (int i = 10; i < 20; i++) {
82 int[] widths = L_PATTERNS[i - 10];
83 int[] reversedWidths = new int[widths.length];
84 for (int j = 0; j < widths.length; j++) {
85 reversedWidths[j] = widths[widths.length - j - 1];
87 L_AND_G_PATTERNS[i] = reversedWidths;
91 private final StringBuffer decodeRowStringBuffer;
93 protected UPCEANReader() {
94 decodeRowStringBuffer = new StringBuffer(20);
97 static int[] findStartGuardPattern(BitArray row) throws ReaderException {
98 boolean foundStart = false;
99 int[] startRange = null;
101 while (!foundStart) {
102 startRange = findGuardPattern(row, nextStart, false, START_END_PATTERN);
103 int start = startRange[0];
104 nextStart = startRange[1];
105 // Make sure there is a quiet zone at least as big as the start pattern before the barcode.
106 // If this check would run off the left edge of the image, do not accept this barcode,
107 // as it is very likely to be a false positive.
108 int quietStart = start - (nextStart - start);
109 if (quietStart >= 0) {
110 foundStart = row.isRange(quietStart, start, false);
116 public Result decodeRow(int rowNumber, BitArray row, Hashtable hints) throws ReaderException {
117 return decodeRow(rowNumber, row, findStartGuardPattern(row), hints);
121 * <p>Like {@link #decodeRow(int, BitArray, java.util.Hashtable)}, but
122 * allows caller to inform method about where the UPC/EAN start pattern is
123 * found. This allows this to be computed once and reused across many implementations.</p>
125 public Result decodeRow(int rowNumber, BitArray row, int[] startGuardRange, Hashtable hints)
126 throws ReaderException {
128 ResultPointCallback resultPointCallback = hints == null ? null :
129 (ResultPointCallback) hints.get(DecodeHintType.NEED_RESULT_POINT_CALLBACK);
131 if (resultPointCallback != null) {
132 resultPointCallback.foundPossibleResultPoint(new ResultPoint(
133 (startGuardRange[0] + startGuardRange[1]) / 2.0f, rowNumber
137 StringBuffer result = decodeRowStringBuffer;
139 int endStart = decodeMiddle(row, startGuardRange, result);
141 if (resultPointCallback != null) {
142 resultPointCallback.foundPossibleResultPoint(new ResultPoint(
147 int[] endRange = decodeEnd(row, endStart);
149 if (resultPointCallback != null) {
150 resultPointCallback.foundPossibleResultPoint(new ResultPoint(
151 (endRange[0] + endRange[1]) / 2.0f, rowNumber
156 // Make sure there is a quiet zone at least as big as the end pattern after the barcode. The
157 // spec might want more whitespace, but in practice this is the maximum we can count on.
158 int end = endRange[1];
159 int quietEnd = end + (end - endRange[0]);
160 if (quietEnd >= row.getSize() || !row.isRange(end, quietEnd, false)) {
161 throw ReaderException.getInstance();
164 String resultString = result.toString();
165 if (!checkChecksum(resultString)) {
166 throw ReaderException.getInstance();
169 float left = (float) (startGuardRange[1] + startGuardRange[0]) / 2.0f;
170 float right = (float) (endRange[1] + endRange[0]) / 2.0f;
171 return new Result(resultString,
172 null, // no natural byte representation for these barcodes
174 new ResultPoint(left, (float) rowNumber),
175 new ResultPoint(right, (float) rowNumber)},
180 * @return {@link #checkStandardUPCEANChecksum(String)}
182 boolean checkChecksum(String s) throws ReaderException {
183 return checkStandardUPCEANChecksum(s);
187 * Computes the UPC/EAN checksum on a string of digits, and reports
188 * whether the checksum is correct or not.
190 * @param s string of digits to check
191 * @return true iff string of digits passes the UPC/EAN checksum algorithm
192 * @throws ReaderException if the string does not contain only digits
194 private static boolean checkStandardUPCEANChecksum(String s) throws ReaderException {
195 int length = s.length();
201 for (int i = length - 2; i >= 0; i -= 2) {
202 int digit = (int) s.charAt(i) - (int) '0';
203 if (digit < 0 || digit > 9) {
204 throw ReaderException.getInstance();
209 for (int i = length - 1; i >= 0; i -= 2) {
210 int digit = (int) s.charAt(i) - (int) '0';
211 if (digit < 0 || digit > 9) {
212 throw ReaderException.getInstance();
216 return sum % 10 == 0;
219 int[] decodeEnd(BitArray row, int endStart) throws ReaderException {
220 return findGuardPattern(row, endStart, false, START_END_PATTERN);
224 * @param row row of black/white values to search
225 * @param rowOffset position to start search
226 * @param whiteFirst if true, indicates that the pattern specifies white/black/white/...
227 * pixel counts, otherwise, it is interpreted as black/white/black/...
228 * @param pattern pattern of counts of number of black and white pixels that are being
229 * searched for as a pattern
230 * @return start/end horizontal offset of guard pattern, as an array of two ints
231 * @throws ReaderException if pattern is not found
233 static int[] findGuardPattern(BitArray row, int rowOffset, boolean whiteFirst, int[] pattern)
234 throws ReaderException {
235 int patternLength = pattern.length;
236 int[] counters = new int[patternLength];
237 int width = row.getSize();
238 boolean isWhite = false;
239 while (rowOffset < width) {
240 isWhite = !row.get(rowOffset);
241 if (whiteFirst == isWhite) {
247 int counterPosition = 0;
248 int patternStart = rowOffset;
249 for (int x = rowOffset; x < width; x++) {
250 boolean pixel = row.get(x);
251 if (pixel ^ isWhite) {
252 counters[counterPosition]++;
254 if (counterPosition == patternLength - 1) {
255 if (patternMatchVariance(counters, pattern, MAX_INDIVIDUAL_VARIANCE) < MAX_AVG_VARIANCE) {
256 return new int[]{patternStart, x};
258 patternStart += counters[0] + counters[1];
259 for (int y = 2; y < patternLength; y++) {
260 counters[y - 2] = counters[y];
262 counters[patternLength - 2] = 0;
263 counters[patternLength - 1] = 0;
268 counters[counterPosition] = 1;
269 isWhite ^= true; // isWhite = !isWhite;
272 throw ReaderException.getInstance();
276 * Attempts to decode a single UPC/EAN-encoded digit.
278 * @param row row of black/white values to decode
279 * @param counters the counts of runs of observed black/white/black/... values
280 * @param rowOffset horizontal offset to start decoding from
281 * @param patterns the set of patterns to use to decode -- sometimes different encodings
282 * for the digits 0-9 are used, and this indicates the encodings for 0 to 9 that should
284 * @return horizontal offset of first pixel beyond the decoded digit
285 * @throws ReaderException if digit cannot be decoded
287 static int decodeDigit(BitArray row, int[] counters, int rowOffset, int[][] patterns)
288 throws ReaderException {
289 recordPattern(row, rowOffset, counters);
290 int bestVariance = MAX_AVG_VARIANCE; // worst variance we'll accept
292 int max = patterns.length;
293 for (int i = 0; i < max; i++) {
294 int[] pattern = patterns[i];
295 int variance = patternMatchVariance(counters, pattern, MAX_INDIVIDUAL_VARIANCE);
296 if (variance < bestVariance) {
297 bestVariance = variance;
301 if (bestMatch >= 0) {
304 throw ReaderException.getInstance();
309 * Get the format of this decoder.
311 * @return The 1D format.
313 abstract BarcodeFormat getBarcodeFormat();
316 * Subclasses override this to decode the portion of a barcode between the start
317 * and end guard patterns.
319 * @param row row of black/white values to search
320 * @param startRange start/end offset of start guard pattern
321 * @param resultString {@link StringBuffer} to append decoded chars to
322 * @return horizontal offset of first pixel after the "middle" that was decoded
323 * @throws ReaderException if decoding could not complete successfully
325 protected abstract int decodeMiddle(BitArray row, int[] startRange, StringBuffer resultString)
326 throws ReaderException;