zxing/csharp/datamatrix/decoder/Decoder.cs

/*
 * Copyright 2007 ZXing authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using com.google.zxing.common;
using com.google.zxing.common.reedsolomon; 

namespace com.google.zxing.datamatrix.decoder
{
    
    /**
     * <p>The main class which implements Data Matrix Code decoding -- as opposed to locating and extracting
     * the Data Matrix Code from an image.</p>
     *
     * @author bbrown@google.com (Brian Brown)
     */
    public sealed class Decoder
    {
          private ReedSolomonDecoder rsDecoder;
          public Decoder() {
            rsDecoder = new ReedSolomonDecoder(GF256.DATA_MATRIX_FIELD);
          }

          /**
           * <p>Convenience method that can decode a Data Matrix Code represented as a 2D array of booleans.
           * "true" is taken to mean a black module.</p>
           *
           * @param image booleans representing white/black Data Matrix Code modules
           * @return text and bytes encoded within the Data Matrix Code
           * @throws ReaderException if the Data Matrix Code cannot be decoded
           */
          public DecoderResult decode(bool[][] image) {
            int dimension = image.Length;
            BitMatrix bits = new BitMatrix(dimension);
            for (int i = 0; i < dimension; i++) {
              for (int j = 0; j < dimension; j++) {
                if (image[i][j]) {
                  bits.set(i, j);
                }
              }
            }
            return decode(bits);
          }

          /**
           * <p>Decodes a Data Matrix Code represented as a {@link BitMatrix}. A 1 or "true" is taken
           * to mean a black module.</p>
           *
           * @param bits booleans representing white/black Data Matrix Code modules
           * @return text and bytes encoded within the Data Matrix Code
           * @throws ReaderException if the Data Matrix Code cannot be decoded
           */
          public DecoderResult decode(BitMatrix bits) {

            // Construct a parser and read version, error-correction level
            BitMatrixParser parser = new BitMatrixParser(bits);
            Version version = parser.readVersion(bits);

            // Read codewords
            sbyte[] codewords = parser.readCodewords();
            // Separate into data blocks
            DataBlock[] dataBlocks = DataBlock.getDataBlocks(codewords, version);

            // Count total number of data bytes
            int totalBytes = 0;
            for (int i = 0; i < dataBlocks.Length; i++) {
              totalBytes += dataBlocks[i].getNumDataCodewords();
            }
            sbyte[] resultBytes = new sbyte[totalBytes];
            int resultOffset = 0;

            // Error-correct and copy data blocks together into a stream of bytes
            for (int j = 0; j < dataBlocks.Length; j++) {
              DataBlock dataBlock = dataBlocks[j];
              sbyte[] codewordBytes = dataBlock.getCodewords();
              int numDataCodewords = dataBlock.getNumDataCodewords();
              correctErrors(codewordBytes, numDataCodewords);
              for (int i = 0; i < numDataCodewords; i++) {
                resultBytes[resultOffset++] = codewordBytes[i];
              }
            }

            // Decode the contents of that stream of bytes
            return DecodedBitStreamParser.decode(resultBytes);
          }

          /**
           * <p>Given data and error-correction codewords received, possibly corrupted by errors, attempts to
           * correct the errors in-place using Reed-Solomon error correction.</p>
           *
           * @param codewordBytes data and error correction codewords
           * @param numDataCodewords number of codewords that are data bytes
           * @throws ReaderException if error correction fails
           */
          private void correctErrors(sbyte[] codewordBytes, int numDataCodewords) {
            int numCodewords = codewordBytes.Length;
            // First read into an array of ints
            int[] codewordsInts = new int[numCodewords];
            for (int i = 0; i < numCodewords; i++) {
              codewordsInts[i] = codewordBytes[i] & 0xFF;
            }
            int numECCodewords = codewordBytes.Length - numDataCodewords;
            try {
              rsDecoder.decode(codewordsInts, numECCodewords);
            } catch (ReedSolomonException rse) {
              throw new ReaderException();
            }
            // Copy back into array of bytes -- only need to worry about the bytes that were data
            // We don't care about errors in the error-correction codewords
            for (int i = 0; i < numDataCodewords; i++) {
              codewordBytes[i] = (sbyte) codewordsInts[i];
            }
          }

    }
}