boofcv.alg.fiducial.qrcode

Class QrCodePolynomialMath

java.lang.Object

boofcv.alg.fiducial.qrcode.QrCodePolynomialMath

public class QrCodePolynomialMath
extends java.lang.Object

Contains all the formulas for encoding and decoding BCH and Reid-Solomon codes. For a more accessible introduction to this material see [1] and [2].

 [1] S. A. Tretter "Introduction to Bose Chaudhuri Hocquenghem codes" Goddard Space Flight Center, September 1967
 [2] https://en.wikiversity.org/wiki/Reed–Solomon_codes_for_coders
 

Field Summary

Fields

Modifier and Type	Field and Description
static int	FORMAT_GENERATOR
static int	FORMAT_MASK
static int	VERSION_GENERATOR

Constructor Summary

Constructors

Constructor and Description
QrCodePolynomialMath()

Method Summary

Modifier and Type	Method and Description
static int	bitPolyModulus(int data, int generator, int totalBits, int dataBits) Performs division using xcr operators on the encoded polynomials.
static boolean	checkFormatBits(int bitsNoMask) Check the format bits.
static boolean	checkVersionBits(int bits) Encodes the version bits.
static int	correctDCH(int N, int messageNoMask, int generator, int totalBits, int dataBits) Applies a brute force algorithm to find the message which has the smallest hamming distance.
static int	correctFormatBits(int bitsNoMask) Attempts to correct format bit sequence.
static int	correctVersionBits(int bits) Attempts to correct version bit sequence.
static void	decodeFormatMessage(int message, QrCode qr) Assumes that the format message has no errors in it and decodes its data and saves it into the qr code
static int	encodeFormatBits(QrCode.ErrorLevel level, int mask) Encodes the format bits.
static int	encodeVersionBits(int version) Encodes the version bits.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

FORMAT_GENERATOR

public static final int FORMAT_GENERATOR

See Also:

Constant Field Values

FORMAT_MASK

public static final int FORMAT_MASK

See Also:

Constant Field Values

VERSION_GENERATOR

public static final int VERSION_GENERATOR

See Also:

Constant Field Values

Constructor Detail

QrCodePolynomialMath

public QrCodePolynomialMath()

Method Detail

encodeVersionBits

public static int encodeVersionBits(int version)

Encodes the version bits. BCH(18,6)

Parameters:

version - QR code version. 7 to 40

Returns:

encoded bit field

checkVersionBits

public static boolean checkVersionBits(int bits)

Encodes the version bits. BCH(18,6)

Parameters:

bits - Read in bits. Should encode 18-bits

Returns:

encoded bit field

correctVersionBits

public static int correctVersionBits(int bits)

Attempts to correct version bit sequence.

Parameters:

bits - Read in bits after removing the mask

Returns:

If the message could be corrected, th 5-bit format message. -1 if it couldn't

encodeFormatBits

public static int encodeFormatBits(QrCode.ErrorLevel level,
                                   int mask)

Encodes the format bits. BCH(15,5)

Parameters:

level - Error correction level

mask - The type of mask that is applied to the qr code

Returns:

encoded bit field

checkFormatBits

public static boolean checkFormatBits(int bitsNoMask)

Check the format bits. BCH(15,5) code.

decodeFormatMessage

public static void decodeFormatMessage(int message,
                                       QrCode qr)

Assumes that the format message has no errors in it and decodes its data and saves it into the qr code

Parameters:

message - format data bits after the mask has been remove and shifted over 10 bits

qr - Where the results are written to

correctFormatBits

public static int correctFormatBits(int bitsNoMask)

Attempts to correct format bit sequence.

Parameters:

bitsNoMask - Read in bits after removing the mask

Returns:

If the message could be corrected, th 5-bit format message. -1 if it couldn't

correctDCH

public static int correctDCH(int N,
                             int messageNoMask,
                             int generator,
                             int totalBits,
                             int dataBits)

Applies a brute force algorithm to find the message which has the smallest hamming distance. if two messages have the same distance -1 is returned.

Parameters:

N - Number of possible messages. 32 or 64

messageNoMask - The observed message with mask removed

generator - Generator polynomial

totalBits - Total number of bits in the message.

dataBits - Total number of data bits in the message

Returns:

The error corrected message or -1 if it can't be determined.

bitPolyModulus

public static int bitPolyModulus(int data,
                                 int generator,
                                 int totalBits,
                                 int dataBits)

Performs division using xcr operators on the encoded polynomials. used in BCH encoding/decoding

Parameters:

data - Data being checked

generator - Generator polynomial

totalBits - Total number of bits in data

dataBits - Number of data bits. Rest are error correction bits

Returns:

Remainder after polynomial division