/* * 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.qrcode.decoder; import com.google.zxing.ReaderException; import com.google.zxing.common.BitMatrix; import com.google.zxing.common.DecoderResult; import com.google.zxing.common.reedsolomon.GF256; import com.google.zxing.common.reedsolomon.ReedSolomonDecoder; import com.google.zxing.common.reedsolomon.ReedSolomonException; /** *

The main class which implements QR Code decoding -- as opposed to locating and extracting * the QR Code from an image.

* * @author Sean Owen */ public final class Decoder { private final ReedSolomonDecoder rsDecoder; public Decoder() { rsDecoder = new ReedSolomonDecoder(GF256.QR_CODE_FIELD); } /** *

Convenience method that can decode a QR Code represented as a 2D array of booleans. * "true" is taken to mean a black module.

* * @param image booleans representing white/black QR Code modules * @return text and bytes encoded within the QR Code * @throws ReaderException if the QR Code cannot be decoded */ public DecoderResult decode(boolean[][] image) throws ReaderException { 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); } /** *

Decodes a QR Code represented as a {@link BitMatrix}. A 1 or "true" is taken to mean a black module.

* * @param bits booleans representing white/black QR Code modules * @return text and bytes encoded within the QR Code * @throws ReaderException if the QR Code cannot be decoded */ public DecoderResult decode(BitMatrix bits) throws ReaderException { // Construct a parser and read version, error-correction level BitMatrixParser parser = new BitMatrixParser(bits); Version version = parser.readVersion(); ErrorCorrectionLevel ecLevel = parser.readFormatInformation().getErrorCorrectionLevel(); // Read codewords byte[] codewords = parser.readCodewords(); // Separate into data blocks DataBlock[] dataBlocks = DataBlock.getDataBlocks(codewords, version, ecLevel); // Count total number of data bytes int totalBytes = 0; for (int i = 0; i < dataBlocks.length; i++) { totalBytes += dataBlocks[i].getNumDataCodewords(); } byte[] resultBytes = new byte[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]; byte[] 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, version); } /** *

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 ReaderException if error correction fails */ private void correctErrors(byte[] codewordBytes, int numDataCodewords) throws ReaderException { 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 ReaderException.getInstance(); } // 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]; } } }