com.google.zxing.datamatrix.decoder.Decoder Maven / Gradle / Ivy
/*
* 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.
*/
package com.google.zxing.datamatrix.decoder;
import com.google.zxing.ChecksumException;
import com.google.zxing.FormatException;
import com.google.zxing.common.BitMatrix;
import com.google.zxing.common.DecoderResult;
import com.google.zxing.common.reedsolomon.GenericGF;
import com.google.zxing.common.reedsolomon.ReedSolomonDecoder;
import com.google.zxing.common.reedsolomon.ReedSolomonException;
/**
* The main class which implements Data Matrix Code decoding -- as opposed to locating and extracting
* the Data Matrix Code from an image.
*
* @author [email protected] (Brian Brown)
*/
public final class Decoder {
private final ReedSolomonDecoder rsDecoder;
public Decoder() {
rsDecoder = new ReedSolomonDecoder(GenericGF.DATA_MATRIX_FIELD_256);
}
/**
* Convenience method that can decode a Data Matrix Code represented as a 2D array of booleans.
* "true" is taken to mean a black module.
*
* @param image booleans representing white/black Data Matrix Code modules
* @return text and bytes encoded within the Data Matrix Code
* @throws FormatException if the Data Matrix Code cannot be decoded
* @throws ChecksumException if error correction fails
*/
public DecoderResult decode(boolean[][] image) throws FormatException, ChecksumException {
return decode(BitMatrix.parse(image));
}
/**
* Decodes a Data Matrix Code represented as a {@link BitMatrix}. A 1 or "true" is taken
* to mean a black module.
*
* @param bits booleans representing white/black Data Matrix Code modules
* @return text and bytes encoded within the Data Matrix Code
* @throws FormatException if the Data Matrix Code cannot be decoded
* @throws ChecksumException if error correction fails
*/
public DecoderResult decode(BitMatrix bits) throws FormatException, ChecksumException {
// Construct a parser and read version, error-correction level
BitMatrixParser parser = new BitMatrixParser(bits);
Version version = parser.getVersion();
// Read codewords
byte[] codewords = parser.readCodewords();
// Separate into data blocks
DataBlock[] dataBlocks = DataBlock.getDataBlocks(codewords, version);
// Count total number of data bytes
int totalBytes = 0;
for (DataBlock db : dataBlocks) {
totalBytes += db.getNumDataCodewords();
}
byte[] resultBytes = new byte[totalBytes];
int dataBlocksCount = dataBlocks.length;
// Error-correct and copy data blocks together into a stream of bytes
for (int j = 0; j < dataBlocksCount; j++) {
DataBlock dataBlock = dataBlocks[j];
byte[] codewordBytes = dataBlock.getCodewords();
int numDataCodewords = dataBlock.getNumDataCodewords();
correctErrors(codewordBytes, numDataCodewords);
for (int i = 0; i < numDataCodewords; i++) {
// De-interlace data blocks.
resultBytes[i * dataBlocksCount + j] = codewordBytes[i];
}
}
// Decode the contents of that stream of bytes
return DecodedBitStreamParser.decode(resultBytes);
}
/**
* Given data and error-correction codewords received, possibly corrupted by errors, attempts to
* correct the errors in-place using Reed-Solomon error correction.
*
* @param codewordBytes data and error correction codewords
* @param numDataCodewords number of codewords that are data bytes
* @throws ChecksumException if error correction fails
*/
private void correctErrors(byte[] codewordBytes, int numDataCodewords) throws ChecksumException {
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;
}
try {
rsDecoder.decode(codewordsInts, codewordBytes.length - numDataCodewords);
} catch (ReedSolomonException ignored) {
throw ChecksumException.getChecksumInstance();
}
// 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] = (byte) codewordsInts[i];
}
}
}