2 * Copyright 2007 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.qrcode.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.common.reedsolomon.GF256;
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23 import com.google.zxing.common.reedsolomon.ReedSolomonDecoder;
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24 import com.google.zxing.common.reedsolomon.ReedSolomonException;
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26 import java.util.Hashtable;
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29 * <p>The main class which implements QR Code decoding -- as opposed to locating and extracting
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30 * the QR Code from an image.</p>
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34 public final class Decoder {
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36 private final ReedSolomonDecoder rsDecoder;
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39 rsDecoder = new ReedSolomonDecoder(GF256.QR_CODE_FIELD);
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42 public DecoderResult decode(boolean[][] image) throws ReaderException {
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43 return decode(image, null);
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47 * <p>Convenience method that can decode a QR Code represented as a 2D array of booleans.
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48 * "true" is taken to mean a black module.</p>
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50 * @param image booleans representing white/black QR Code modules
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51 * @return text and bytes encoded within the QR Code
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52 * @throws ReaderException if the QR Code cannot be decoded
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54 public DecoderResult decode(boolean[][] image, Hashtable hints) throws ReaderException {
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55 int dimension = image.length;
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56 BitMatrix bits = new BitMatrix(dimension);
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57 for (int i = 0; i < dimension; i++) {
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58 for (int j = 0; j < dimension; j++) {
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64 return decode(bits, hints);
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67 public DecoderResult decode(BitMatrix bits) throws ReaderException {
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68 return decode(bits, null);
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72 * <p>Decodes a QR Code represented as a {@link BitMatrix}. A 1 or "true" is taken to mean a black module.</p>
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74 * @param bits booleans representing white/black QR Code modules
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75 * @return text and bytes encoded within the QR Code
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76 * @throws ReaderException if the QR Code cannot be decoded
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78 public DecoderResult decode(BitMatrix bits, Hashtable hints) throws ReaderException {
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80 // Construct a parser and read version, error-correction level
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81 BitMatrixParser parser = new BitMatrixParser(bits);
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82 Version version = parser.readVersion();
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83 ErrorCorrectionLevel ecLevel = parser.readFormatInformation().getErrorCorrectionLevel();
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86 byte[] codewords = parser.readCodewords();
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87 // Separate into data blocks
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88 DataBlock[] dataBlocks = DataBlock.getDataBlocks(codewords, version, ecLevel);
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90 // Count total number of data bytes
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92 for (int i = 0; i < dataBlocks.length; i++) {
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93 totalBytes += dataBlocks[i].getNumDataCodewords();
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95 byte[] resultBytes = new byte[totalBytes];
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96 int resultOffset = 0;
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98 // Error-correct and copy data blocks together into a stream of bytes
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99 for (int j = 0; j < dataBlocks.length; j++) {
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100 DataBlock dataBlock = dataBlocks[j];
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101 byte[] codewordBytes = dataBlock.getCodewords();
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102 int numDataCodewords = dataBlock.getNumDataCodewords();
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103 correctErrors(codewordBytes, numDataCodewords);
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104 for (int i = 0; i < numDataCodewords; i++) {
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105 resultBytes[resultOffset++] = codewordBytes[i];
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109 // Decode the contents of that stream of bytes
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110 return DecodedBitStreamParser.decode(resultBytes, version, ecLevel, hints);
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114 * <p>Given data and error-correction codewords received, possibly corrupted by errors, attempts to
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115 * correct the errors in-place using Reed-Solomon error correction.</p>
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117 * @param codewordBytes data and error correction codewords
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118 * @param numDataCodewords number of codewords that are data bytes
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119 * @throws ReaderException if error correction fails
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121 private void correctErrors(byte[] codewordBytes, int numDataCodewords) throws ReaderException {
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122 int numCodewords = codewordBytes.length;
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123 // First read into an array of ints
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124 int[] codewordsInts = new int[numCodewords];
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125 for (int i = 0; i < numCodewords; i++) {
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126 codewordsInts[i] = codewordBytes[i] & 0xFF;
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128 int numECCodewords = codewordBytes.length - numDataCodewords;
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130 rsDecoder.decode(codewordsInts, numECCodewords);
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131 } catch (ReedSolomonException rse) {
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132 throw ReaderException.getInstance();
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134 // Copy back into array of bytes -- only need to worry about the bytes that were data
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135 // We don't care about errors in the error-correction codewords
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136 for (int i = 0; i < numDataCodewords; i++) {
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137 codewordBytes[i] = (byte) codewordsInts[i];
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