/*
* 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.ChecksumException;
import com.google.zxing.DecodeHintType;
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;
import java.util.Map;
/**
* <p>The main class which implements QR Code decoding -- as opposed to locating and extracting
* the QR Code from an image.</p>
*
* @author Sean Owen
*/
public final class Decoder {
private final ReedSolomonDecoder rsDecoder;
public Decoder() {
rsDecoder = new ReedSolomonDecoder(GenericGF.QR_CODE_FIELD_256);
}
public DecoderResult decode(boolean[][] image) throws ChecksumException, FormatException {
return decode(image, null);
}
/**
* <p>Convenience method that can decode a QR Code represented as a 2D array of booleans.
* "true" is taken to mean a black module.</p>
*
* @param image booleans representing white/black QR Code modules
* @param hints decoding hints that should be used to influence decoding
* @return text and bytes encoded within the QR Code
* @throws FormatException if the QR Code cannot be decoded
* @throws ChecksumException if error correction fails
*/
public DecoderResult decode(boolean[][] image, Map<DecodeHintType,?> hints)
throws ChecksumException, FormatException {
return decode(BitMatrix.parse(image), hints);
}
public DecoderResult decode(BitMatrix bits) throws ChecksumException, FormatException {
return decode(bits, null);
}
/**
* <p>Decodes a QR Code represented as a {@link BitMatrix}. A 1 or "true" is taken to mean a black module.</p>
*
* @param bits booleans representing white/black QR Code modules
* @param hints decoding hints that should be used to influence decoding
* @return text and bytes encoded within the QR Code
* @throws FormatException if the QR Code cannot be decoded
* @throws ChecksumException if error correction fails
*/
public DecoderResult decode(BitMatrix bits, Map<DecodeHintType,?> hints)
throws FormatException, ChecksumException {
// Construct a parser and read version, error-correction level
BitMatrixParser parser = new BitMatrixParser(bits);
FormatException fe = null;
ChecksumException ce = null;
try {
return decode(parser, hints);
} catch (FormatException e) {
fe = e;
} catch (ChecksumException e) {
ce = e;
}
try {
// Revert the bit matrix
parser.remask();
// Will be attempting a mirrored reading of the version and format info.
parser.setMirror(true);
// Preemptively read the version.
parser.readVersion();
// Preemptively read the format information.
parser.readFormatInformation();
/*
* Since we're here, this means we have successfully detected some kind
* of version and format information when mirrored. This is a good sign,
* that the QR code may be mirrored, and we should try once more with a
* mirrored content.
*/
// Prepare for a mirrored reading.
parser.mirror();
DecoderResult result = decode(parser, hints);
// Success! Notify the caller that the code was mirrored.
result.setOther(new QRCodeDecoderMetaData(true));
return result;
} catch (FormatException | ChecksumException e) {
// Throw the exception from the original reading
if (fe != null) {
throw fe;
}
if (ce != null) {
throw ce;
}
throw e;
}
}
private DecoderResult decode(BitMatrixParser parser, Map<DecodeHintType,?> hints)
throws FormatException, ChecksumException {
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 (DataBlock dataBlock : dataBlocks) {
totalBytes += dataBlock.getNumDataCodewords();
}
byte[] resultBytes = new byte[totalBytes];
int resultOffset = 0;
// Error-correct and copy data blocks together into a stream of bytes
for (DataBlock dataBlock : dataBlocks) {
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, ecLevel, hints);
}
/**
* <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 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];
}
}
}
