Added code for the Data Matrix decoder.

[zxing.git] / core / src / com / google / zxing / datamatrix / decoder / Decoder.java

diff --git a/core/src/com/google/zxing/datamatrix/decoder/Decoder.java b/core/src/com/google/zxing/datamatrix/decoder/Decoder.java
new file mode 100644 (file)
index 0000000..3280eb6
--- /dev/null
+++ b/core/src/com/google/zxing/datamatrix/decoder/Decoder.java
@@ -0,0 +1,130 @@
+/*\r
+ * Copyright 2007 Google Inc.\r
+ *\r
+ * Licensed under the Apache License, Version 2.0 (the "License");\r
+ * you may not use this file except in compliance with the License.\r
+ * You may obtain a copy of the License at\r
+ *\r
+ *      http://www.apache.org/licenses/LICENSE-2.0\r
+ *\r
+ * Unless required by applicable law or agreed to in writing, software\r
+ * distributed under the License is distributed on an "AS IS" BASIS,\r
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\r
+ * See the License for the specific language governing permissions and\r
+ * limitations under the License.\r
+ */\r
+\r
+package com.google.zxing.datamatrix.decoder;\r
+\r
+import com.google.zxing.ReaderException;\r
+import com.google.zxing.common.BitMatrix;\r
+import com.google.zxing.common.reedsolomon.GF256;\r
+import com.google.zxing.common.reedsolomon.ReedSolomonDecoder;\r
+import com.google.zxing.common.reedsolomon.ReedSolomonException;\r
+\r
+/**\r
+ * <p>The main class which implements Data Matrix Code decoding -- as opposed to locating and extracting\r
+ * the Data Matrix Code from an image.</p>\r
+ *\r
+ * @author bbrown@google.com (Brian Brown)\r
+ */\r
+public final class Decoder {\r
+\r
+  private final ReedSolomonDecoder rsDecoder;\r
+\r
+  public Decoder() {\r
+    rsDecoder = new ReedSolomonDecoder(GF256.DATA_MATRIX_FIELD);\r
+  }\r
+\r
+  /**\r
+   * <p>Convenience method that can decode a Data Matrix Code represented as a 2D array of booleans.\r
+   * "true" is taken to mean a black module.</p>\r
+   *\r
+   * @param image booleans representing white/black Data Matrix Code modules\r
+   * @return text encoded within the Data Matrix Code\r
+   * @throws ReaderException if the Data Matrix Code cannot be decoded\r
+   */\r
+  public String decode(boolean[][] image) throws ReaderException {\r
+    int dimension = image.length;\r
+    BitMatrix bits = new BitMatrix(dimension);\r
+    for (int i = 0; i < dimension; i++) {\r
+      for (int j = 0; j < dimension; j++) {\r
+        if (image[i][j]) {\r
+          bits.set(i, j);\r
+        }\r
+      }\r
+    }\r
+    return decode(bits);\r
+  }\r
+\r
+  /**\r
+   * <p>Decodes a Data Matrix Code represented as a {@link BitMatrix}. A 1 or "true" is taken\r
+   * to mean a black module.</p>\r
+   *\r
+   * @param bits booleans representing white/black Data Matrix Code modules\r
+   * @return text encoded within the Data Matrix Code\r
+   * @throws ReaderException if the Data Matrix Code cannot be decoded\r
+   */\r
+  public String decode(BitMatrix bits) throws ReaderException {\r
+\r
+    // Construct a parser and read version, error-correction level\r
+    BitMatrixParser parser = new BitMatrixParser(bits);\r
+    Version version = parser.readVersion(bits);\r
+\r
+    // Read codewords\r
+    byte[] codewords = parser.readCodewords();\r
+    // Separate into data blocks\r
+    DataBlock[] dataBlocks = DataBlock.getDataBlocks(codewords, version);\r
+\r
+    // Count total number of data bytes\r
+    int totalBytes = 0;\r
+    for (int i = 0; i < dataBlocks.length; i++) {\r
+      totalBytes += dataBlocks[i].getNumDataCodewords();\r
+    }\r
+    byte[] resultBytes = new byte[totalBytes];\r
+    int resultOffset = 0;\r
+\r
+    // Error-correct and copy data blocks together into a stream of bytes\r
+    for (int j = 0; j < dataBlocks.length; j++) {\r
+      DataBlock dataBlock = dataBlocks[j];\r
+      byte[] codewordBytes = dataBlock.getCodewords();\r
+      int numDataCodewords = dataBlock.getNumDataCodewords();\r
+      correctErrors(codewordBytes, numDataCodewords);\r
+      for (int i = 0; i < numDataCodewords; i++) {\r
+        resultBytes[resultOffset++] = codewordBytes[i];\r
+      }\r
+    }\r
+\r
+    // Decode the contents of that stream of bytes\r
+    return DecodedBitStreamParser.decode(resultBytes);\r
+  }\r
+\r
+  /**\r
+   * <p>Given data and error-correction codewords received, possibly corrupted by errors, attempts to\r
+   * correct the errors in-place using Reed-Solomon error correction.</p>\r
+   *\r
+   * @param codewordBytes data and error correction codewords\r
+   * @param numDataCodewords number of codewords that are data bytes\r
+   * @throws ReaderException if error correction fails\r
+   */\r
+  private void correctErrors(byte[] codewordBytes, int numDataCodewords) throws ReaderException {\r
+    int numCodewords = codewordBytes.length;\r
+    // First read into an array of ints\r
+    int[] codewordsInts = new int[numCodewords];\r
+    for (int i = 0; i < numCodewords; i++) {\r
+      codewordsInts[i] = codewordBytes[i] & 0xFF;\r
+    }\r
+    int numECCodewords = codewordBytes.length - numDataCodewords;\r
+    try {\r
+      rsDecoder.decode(codewordsInts, numECCodewords);\r
+    } catch (ReedSolomonException rse) {\r
+      throw new ReaderException(rse.toString());\r
+    }\r
+    // Copy back into array of bytes -- only need to worry about the bytes that were data\r
+    // We don't care about errors in the error-correction codewords\r
+    for (int i = 0; i < numDataCodewords; i++) {\r
+      codewordBytes[i] = (byte) codewordsInts[i];\r
+    }\r
+  }\r
+\r
+}\r