2 * Copyright 2007 Google Inc.
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4 * Licensed under the Apache License, Version 2.0 (the "License");
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5 * you may not use this file except in compliance with the License.
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6 * You may obtain a copy of the License at
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8 * http://www.apache.org/licenses/LICENSE-2.0
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10 * Unless required by applicable law or agreed to in writing, software
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11 * distributed under the License is distributed on an "AS IS" BASIS,
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12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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13 * See the License for the specific language governing permissions and
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14 * limitations under the License.
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17 package com.google.zxing.datamatrix.decoder;
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19 import com.google.zxing.ReaderException;
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20 import com.google.zxing.common.BitMatrix;
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21 import com.google.zxing.common.reedsolomon.GF256;
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22 import com.google.zxing.common.reedsolomon.ReedSolomonDecoder;
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23 import com.google.zxing.common.reedsolomon.ReedSolomonException;
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26 * <p>The main class which implements Data Matrix Code decoding -- as opposed to locating and extracting
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27 * the Data Matrix Code from an image.</p>
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29 * @author bbrown@google.com (Brian Brown)
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31 public final class Decoder {
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33 private final ReedSolomonDecoder rsDecoder;
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36 rsDecoder = new ReedSolomonDecoder(GF256.DATA_MATRIX_FIELD);
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40 * <p>Convenience method that can decode a Data Matrix Code represented as a 2D array of booleans.
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41 * "true" is taken to mean a black module.</p>
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43 * @param image booleans representing white/black Data Matrix Code modules
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44 * @return text encoded within the Data Matrix Code
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45 * @throws ReaderException if the Data Matrix Code cannot be decoded
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47 public String decode(boolean[][] image) throws ReaderException {
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48 int dimension = image.length;
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49 BitMatrix bits = new BitMatrix(dimension);
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50 for (int i = 0; i < dimension; i++) {
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51 for (int j = 0; j < dimension; j++) {
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57 return decode(bits);
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61 * <p>Decodes a Data Matrix Code represented as a {@link BitMatrix}. A 1 or "true" is taken
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62 * to mean a black module.</p>
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64 * @param bits booleans representing white/black Data Matrix Code modules
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65 * @return text encoded within the Data Matrix Code
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66 * @throws ReaderException if the Data Matrix Code cannot be decoded
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68 public String decode(BitMatrix bits) throws ReaderException {
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70 // Construct a parser and read version, error-correction level
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71 BitMatrixParser parser = new BitMatrixParser(bits);
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72 Version version = parser.readVersion(bits);
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75 byte[] codewords = parser.readCodewords();
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76 // Separate into data blocks
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77 DataBlock[] dataBlocks = DataBlock.getDataBlocks(codewords, version);
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79 // Count total number of data bytes
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81 for (int i = 0; i < dataBlocks.length; i++) {
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82 totalBytes += dataBlocks[i].getNumDataCodewords();
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84 byte[] resultBytes = new byte[totalBytes];
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85 int resultOffset = 0;
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87 // Error-correct and copy data blocks together into a stream of bytes
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88 for (int j = 0; j < dataBlocks.length; j++) {
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89 DataBlock dataBlock = dataBlocks[j];
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90 byte[] codewordBytes = dataBlock.getCodewords();
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91 int numDataCodewords = dataBlock.getNumDataCodewords();
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92 correctErrors(codewordBytes, numDataCodewords);
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93 for (int i = 0; i < numDataCodewords; i++) {
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94 resultBytes[resultOffset++] = codewordBytes[i];
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98 // Decode the contents of that stream of bytes
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99 return DecodedBitStreamParser.decode(resultBytes);
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103 * <p>Given data and error-correction codewords received, possibly corrupted by errors, attempts to
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104 * correct the errors in-place using Reed-Solomon error correction.</p>
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106 * @param codewordBytes data and error correction codewords
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107 * @param numDataCodewords number of codewords that are data bytes
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108 * @throws ReaderException if error correction fails
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110 private void correctErrors(byte[] codewordBytes, int numDataCodewords) throws ReaderException {
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111 int numCodewords = codewordBytes.length;
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112 // First read into an array of ints
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113 int[] codewordsInts = new int[numCodewords];
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114 for (int i = 0; i < numCodewords; i++) {
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115 codewordsInts[i] = codewordBytes[i] & 0xFF;
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117 int numECCodewords = codewordBytes.length - numDataCodewords;
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119 rsDecoder.decode(codewordsInts, numECCodewords);
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120 } catch (ReedSolomonException rse) {
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121 throw new ReaderException(rse.toString());
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123 // Copy back into array of bytes -- only need to worry about the bytes that were data
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124 // We don't care about errors in the error-correction codewords
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125 for (int i = 0; i < numDataCodewords; i++) {
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126 codewordBytes[i] = (byte) codewordsInts[i];
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