2 * Copyright 2009 ZXing authors
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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.pdf417.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.DecoderResult;
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22 //import com.google.zxing.pdf417.reedsolomon.ReedSolomonDecoder;
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25 * <p>The main class which implements PDF417 Code decoding -- as
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26 * opposed to locating and extracting the PDF417 Code from an image.</p>
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28 * @author SITA Lab (kevin.osullivan@sita.aero)
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30 public final class Decoder {
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32 private static final int MAX_ERRORS = 3;
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33 private static final int MAX_EC_CODEWORDS = 512;
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34 //private final ReedSolomonDecoder rsDecoder;
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38 //rsDecoder = new ReedSolomonDecoder();
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42 * <p>Convenience method that can decode a PDF417 Code represented as a 2D array of booleans.
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43 * "true" is taken to mean a black module.</p>
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45 * @param image booleans representing white/black PDF417 modules
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46 * @return text and bytes encoded within the PDF417 Code
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47 * @throws ReaderException if the PDF417 Code cannot be decoded
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49 public DecoderResult decode(boolean[][] image) throws ReaderException {
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50 int dimension = image.length;
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51 BitMatrix bits = new BitMatrix(dimension);
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52 for (int i = 0; i < dimension; i++) {
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53 for (int j = 0; j < dimension; j++) {
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59 return decode(bits);
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63 * <p>Decodes a PDF417 Code represented as a {@link BitMatrix}.
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64 * A 1 or "true" is taken to mean a black module.</p>
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66 * @param bits booleans representing white/black PDF417 Code modules
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67 * @return text and bytes encoded within the PDF417 Code
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68 * @throws ReaderException if the PDF417 Code cannot be decoded
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70 public DecoderResult decode(BitMatrix bits) throws ReaderException {
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71 // Construct a parser to read the data codewords and error-correction level
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72 BitMatrixParser parser = new BitMatrixParser(bits);
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73 int[] codewords = parser.readCodewords();
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74 if (codewords == null || codewords.length == 0) {
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75 throw ReaderException.getInstance();
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78 int ecLevel = parser.getECLevel();
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79 int numECCodewords = 1 << (ecLevel + 1);
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80 int[] erasures = parser.getErasures();
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82 correctErrors(codewords, erasures, numECCodewords);
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83 verifyCodewordCount(codewords, numECCodewords);
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85 // Decode the codewords
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86 return DecodedBitStreamParser.decode(codewords);
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90 * Verify that all is OK with the codeword array.
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93 * @return an index to the first data codeword.
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94 * @throws ReaderException
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96 private static int verifyCodewordCount(int[] codewords, int numECCodewords) throws ReaderException {
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97 if (codewords.length < 4) {
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98 // Codeword array size should be at least 4 allowing for
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99 // Count CW, At least one Data CW, Error Correction CW, Error Correction CW
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100 throw ReaderException.getInstance();
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102 // The first codeword, the Symbol Length Descriptor, shall always encode the total number of data
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103 // codewords in the symbol, including the Symbol Length Descriptor itself, data codewords and pad
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104 // codewords, but excluding the number of error correction codewords.
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105 int numberOfCodewords = codewords[0];
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106 if (numberOfCodewords > codewords.length) {
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107 throw ReaderException.getInstance();
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109 if (numberOfCodewords == 0) {
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110 // Reset to the length of the array - 8 (Allow for at least level 3 Error Correction (8 Error Codewords)
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111 if (numECCodewords < codewords.length) {
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112 codewords[0] = codewords.length - numECCodewords;
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114 throw ReaderException.getInstance();
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117 return 1; // Index to first data codeword
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121 * <p>Given data and error-correction codewords received, possibly corrupted by errors, attempts to
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122 * correct the errors in-place using Reed-Solomon error correction.</p>
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124 * @param codewords data and error correction codewords
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125 * @throws ReaderException if error correction fails
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127 private static int correctErrors(int[] codewords, int[] erasures, int numECCodewords) throws ReaderException {
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128 if ((erasures != null && erasures.length > numECCodewords / 2 + MAX_ERRORS) ||
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129 (numECCodewords < 0 || numECCodewords > MAX_EC_CODEWORDS)) {
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130 // Too many errors or EC Codewords is corrupted
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131 throw ReaderException.getInstance();
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133 // Try to correct the errors
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134 int result = 0; // rsDecoder.correctErrors(codewords, numECCodewords);
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135 if (erasures != null) {
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136 int numErasures = erasures.length;
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138 numErasures -= result;
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140 if (numErasures > MAX_ERRORS) {
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141 // Still too many errors
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142 throw ReaderException.getInstance();
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