csharp/pdf417/decoder/Decoder.cs

   1 /*\r
   2 * Copyright 2009 ZXing authors\r
   3 *\r
   4 * Licensed under the Apache License, Version 2.0 (the "License");\r
   5 * you may not use this file except in compliance with the License.\r
   6 * You may obtain a copy of the License at\r
   7 *\r
   8 *      http://www.apache.org/licenses/LICENSE-2.0\r
   9 *\r
  10 * Unless required by applicable law or agreed to in writing, software\r
  11 * distributed under the License is distributed on an "AS IS" BASIS,\r
  12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\r
  13 * See the License for the specific language governing permissions and\r
  14 * limitations under the License.\r
  15 */\r
  16 using System;\r
  17 using ReaderException = com.google.zxing.ReaderException;\r
  18 using BitMatrix = com.google.zxing.common.BitMatrix;\r
  19 using DecoderResult = com.google.zxing.common.DecoderResult;\r
  20 namespace com.google.zxing.pdf417.decoder\r
  21 {\r
  22         //import com.google.zxing.pdf417.reedsolomon.ReedSolomonDecoder;\r
  23         \r
  24         /// <summary> <p>The main class which implements PDF417 Code decoding -- as\r
  25         /// opposed to locating and extracting the PDF417 Code from an image.</p>\r
  26         /// \r
  27         /// </summary>\r
  28         /// <author>  SITA Lab (kevin.osullivan@sita.aero)\r
  29         /// </author>\r
  30         /// <author>www.Redivivus.in (suraj.supekar@redivivus.in) - Ported from ZXING Java Source \r
  31         /// </author>\r
  32         public sealed class Decoder\r
  33         {\r
  34                 \r
  35                 private const int MAX_ERRORS = 3;\r
  36                 private const int MAX_EC_CODEWORDS = 512;\r
  37                 //private final ReedSolomonDecoder rsDecoder;\r
  38                 \r
  39                 public Decoder()\r
  40                 {\r
  41                         // TODO MGMG\r
  42                         //rsDecoder = new ReedSolomonDecoder();\r
  43                 }\r
  44                 \r
  45                 /// <summary> <p>Convenience method that can decode a PDF417 Code represented as a 2D array of booleans.\r
  46                 /// "true" is taken to mean a black module.</p>\r
  47                 /// \r
  48                 /// </summary>\r
  49                 /// <param name="image">booleans representing white/black PDF417 modules\r
  50                 /// </param>\r
  51                 /// <returns> text and bytes encoded within the PDF417 Code\r
  52                 /// </returns>\r
  53                 /// <throws>  ReaderException if the PDF417 Code cannot be decoded </throws>\r
  54                 public DecoderResult decode(bool[][] image)\r
  55                 {\r
  56                         int dimension = image.Length;\r
  57                         BitMatrix bits = new BitMatrix(dimension);\r
  58                         for (int i = 0; i < dimension; i++)\r
  59                         {\r
  60                                 for (int j = 0; j < dimension; j++)\r
  61                                 {\r
  62                                         if (image[j][i])\r
  63                                         {\r
  64                                                 bits.set_Renamed(j, i);\r
  65                                         }\r
  66                                 }\r
  67                         }\r
  68                         return decode(bits);\r
  69                 }\r
  70                 \r
  71                 /// <summary> <p>Decodes a PDF417 Code represented as a {@link BitMatrix}.\r
  72                 /// A 1 or "true" is taken to mean a black module.</p>\r
  73                 /// \r
  74                 /// </summary>\r
  75                 /// <param name="bits">booleans representing white/black PDF417 Code modules\r
  76                 /// </param>\r
  77                 /// <returns> text and bytes encoded within the PDF417 Code\r
  78                 /// </returns>\r
  79                 /// <throws>  ReaderException if the PDF417 Code cannot be decoded </throws>\r
  80                 public DecoderResult decode(BitMatrix bits)\r
  81                 {\r
  82                         // Construct a parser to read the data codewords and error-correction level\r
  83                         BitMatrixParser parser = new BitMatrixParser(bits);\r
  84                         int[] codewords = parser.readCodewords();\r
  85                         if (codewords == null || codewords.Length == 0)\r
  86                         {\r
  87                                 throw ReaderException.Instance;\r
  88                         }\r
  89                         \r
  90                         int ecLevel = parser.ECLevel;\r
  91                         int numECCodewords = 1 << (ecLevel + 1);\r
  92                         int[] erasures = parser.Erasures;\r
  93                         \r
  94                         correctErrors(codewords, erasures, numECCodewords);\r
  95                         verifyCodewordCount(codewords, numECCodewords);\r
  96                         \r
  97                         // Decode the codewords\r
  98                         return DecodedBitStreamParser.decode(codewords);\r
  99                 }\r
 100                 \r
 101                 /// <summary> Verify that all is OK with the codeword array.\r
 102                 /// \r
 103                 /// </summary>\r
 104                 /// <param name="codewords">\r
 105                 /// </param>\r
 106                 /// <returns> an index to the first data codeword.\r
 107                 /// </returns>\r
 108                 /// <throws>  ReaderException </throws>\r
 109                 private static void  verifyCodewordCount(int[] codewords, int numECCodewords)\r
 110                 {\r
 111                         if (codewords.Length < 4)\r
 112                         {\r
 113                                 // Codeword array size should be at least 4 allowing for\r
 114                                 // Count CW, At least one Data CW, Error Correction CW, Error Correction CW\r
 115                                 throw ReaderException.Instance;\r
 116                         }\r
 117                         // The first codeword, the Symbol Length Descriptor, shall always encode the total number of data\r
 118                         // codewords in the symbol, including the Symbol Length Descriptor itself, data codewords and pad\r
 119                         // codewords, but excluding the number of error correction codewords.\r
 120                         int numberOfCodewords = codewords[0];\r
 121                         if (numberOfCodewords > codewords.Length)\r
 122                         {\r
 123                                 throw ReaderException.Instance;\r
 124                         }\r
 125                         if (numberOfCodewords == 0)\r
 126                         {\r
 127                                 // Reset to the length of the array - 8 (Allow for at least level 3 Error Correction (8 Error Codewords)\r
 128                                 if (numECCodewords < codewords.Length)\r
 129                                 {\r
 130                                         codewords[0] = codewords.Length - numECCodewords;\r
 131                                 }\r
 132                                 else\r
 133                                 {\r
 134                                         throw ReaderException.Instance;\r
 135                                 }\r
 136                         }\r
 137                 }\r
 138                 \r
 139                 /// <summary> <p>Given data and error-correction codewords received, possibly corrupted by errors, attempts to\r
 140                 /// correct the errors in-place using Reed-Solomon error correction.</p>\r
 141                 /// \r
 142                 /// </summary>\r
 143                 /// <param name="codewords">  data and error correction codewords\r
 144                 /// </param>\r
 145                 /// <throws>  ReaderException if error correction fails </throws>\r
 146                 private static int correctErrors(int[] codewords, int[] erasures, int numECCodewords)\r
 147                 {\r
 148                         if ((erasures != null && erasures.Length > numECCodewords / 2 + MAX_ERRORS) || (numECCodewords < 0 || numECCodewords > MAX_EC_CODEWORDS))\r
 149                         {\r
 150                                 // Too many errors or EC Codewords is corrupted\r
 151                                 throw ReaderException.Instance;\r
 152                         }\r
 153                         // Try to correct the errors\r
 154                         int result = 0; // rsDecoder.correctErrors(codewords, numECCodewords);\r
 155                         if (erasures != null)\r
 156                         {\r
 157                                 int numErasures = erasures.Length;\r
 158                                 if (result > 0)\r
 159                                 {\r
 160                                         numErasures -= result;\r
 161                                 }\r
 162                                 if (numErasures > MAX_ERRORS)\r
 163                                 {\r
 164                                         // Still too many errors\r
 165                                         throw ReaderException.Instance;\r
 166                                 }\r
 167                         }\r
 168                         return result;\r
 169                 }\r
 170         }\r
 171 }