/*
* Copyright 2009 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.pdf417.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.pdf417.decoder.ec.ErrorCorrection;
/**
* <p>The main class which implements PDF417 Code decoding -- as
* opposed to locating and extracting the PDF417 Code from an image.</p>
*
* @author SITA Lab (kevin.osullivan@sita.aero)
*/
public final class Decoder {
private static final int MAX_ERRORS = 3;
private static final int MAX_EC_CODEWORDS = 512;
private final ErrorCorrection errorCorrection;
public Decoder() {
errorCorrection = new ErrorCorrection();
}
/**
* <p>Convenience method that can decode a PDF417 Code represented as a 2D array of booleans.
* "true" is taken to mean a black module.</p>
*
* @param image booleans representing white/black PDF417 modules
* @return text and bytes encoded within the PDF417 Code
*/
public DecoderResult decode(boolean[][] image) throws FormatException, ChecksumException {
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[j][i]) {
bits.set(j, i);
}
}
}
return decode(bits);
}
/**
* <p>Decodes a PDF417 Code represented as a {@link BitMatrix}.
* A 1 or "true" is taken to mean a black module.</p>
*
* @param bits booleans representing white/black PDF417 Code modules
* @return text and bytes encoded within the PDF417 Code
* @throws FormatException if the PDF417 Code cannot be decoded
*/
public DecoderResult decode(BitMatrix bits) throws FormatException, ChecksumException {
// Construct a parser to read the data codewords and error-correction level
BitMatrixParser parser = new BitMatrixParser(bits);
int[] codewords = parser.readCodewords();
if (codewords.length == 0) {
throw FormatException.getFormatInstance();
}
int ecLevel = parser.getECLevel();
int numECCodewords = 1 << (ecLevel + 1);
int[] erasures = parser.getErasures();
correctErrors(codewords, erasures, numECCodewords);
verifyCodewordCount(codewords, numECCodewords);
// Decode the codewords
return DecodedBitStreamParser.decode(codewords);
}
/**
* Verify that all is OK with the codeword array.
*
* @param codewords
* @return an index to the first data codeword.
*/
private static void verifyCodewordCount(int[] codewords, int numECCodewords) throws FormatException {
if (codewords.length < 4) {
// Codeword array size should be at least 4 allowing for
// Count CW, At least one Data CW, Error Correction CW, Error Correction CW
throw FormatException.getFormatInstance();
}
// The first codeword, the Symbol Length Descriptor, shall always encode the total number of data
// codewords in the symbol, including the Symbol Length Descriptor itself, data codewords and pad
// codewords, but excluding the number of error correction codewords.
int numberOfCodewords = codewords[0];
if (numberOfCodewords > codewords.length) {
throw FormatException.getFormatInstance();
}
if (numberOfCodewords == 0) {
// Reset to the length of the array - 8 (Allow for at least level 3 Error Correction (8 Error Codewords)
if (numECCodewords < codewords.length) {
codewords[0] = codewords.length - numECCodewords;
} else {
throw FormatException.getFormatInstance();
}
}
}
/**
* <p>Given data and error-correction codewords received, possibly corrupted by errors, attempts to
* correct the errors in-place.</p>
*
* @param codewords data and error correction codewords
* @param erasures positions of any known erasures
* @param numECCodewords number of error correction codewards that were available in codewords
* @throws ChecksumException if error correction fails
*/
private void correctErrors(int[] codewords,
int[] erasures,
int numECCodewords) throws ChecksumException {
if (erasures.length > numECCodewords / 2 + MAX_ERRORS ||
numECCodewords < 0 || numECCodewords > MAX_EC_CODEWORDS) {
// Too many errors or EC Codewords is corrupted
throw ChecksumException.getChecksumInstance();
}
errorCorrection.decode(codewords, numECCodewords, erasures);
}
}