com.google.zxing.qrcode.detector

Class FinderPatternFinder

java.lang.Object

com.google.zxing.qrcode.detector.FinderPatternFinder

public class FinderPatternFinder
extends Object

This class attempts to find finder patterns in a QR Code. Finder patterns are the square markers at three corners of a QR Code.

This class is thread-safe but not reentrant. Each thread must allocate its own object.

Author:

Sean Owen

Field Summary

Fields

Modifier and Type	Field and Description
protected static int	MAX_MODULES
protected static int	MIN_SKIP

Constructor Summary

Constructors

Constructor and Description
FinderPatternFinder(BitMatrix image) Creates a finder that will search the image for three finder patterns.
FinderPatternFinder(BitMatrix image, ResultPointCallback resultPointCallback)

Method Summary

Methods

Modifier and Type	Method and Description
protected static boolean	foundPatternCross(int[] stateCount)
protected BitMatrix	getImage()
protected List<FinderPattern>	getPossibleCenters()
protected boolean	handlePossibleCenter(int[] stateCount, int i, int j, boolean pureBarcode) This is called when a horizontal scan finds a possible alignment pattern.

Methods inherited from class java.lang.Object

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

Field Detail

MIN_SKIP

protected static final int MIN_SKIP

See Also:

Constant Field Values

MAX_MODULES

protected static final int MAX_MODULES

See Also:

Constant Field Values

Constructor Detail

FinderPatternFinder

public FinderPatternFinder(BitMatrix image)

Creates a finder that will search the image for three finder patterns.

Parameters:

image - image to search

FinderPatternFinder

public FinderPatternFinder(BitMatrix image,
                   ResultPointCallback resultPointCallback)

Method Detail

getImage

protected final BitMatrix getImage()

getPossibleCenters

protected final List<FinderPattern> getPossibleCenters()

foundPatternCross

protected static boolean foundPatternCross(int[] stateCount)

Parameters:

stateCount - count of black/white/black/white/black pixels just read

Returns:

true iff the proportions of the counts is close enough to the 1/1/3/1/1 ratios used by finder patterns to be considered a match

handlePossibleCenter

protected final boolean handlePossibleCenter(int[] stateCount,
                           int i,
                           int j,
                           boolean pureBarcode)

This is called when a horizontal scan finds a possible alignment pattern. It will cross check with a vertical scan, and if successful, will, ah, cross-cross-check with another horizontal scan. This is needed primarily to locate the real horizontal center of the pattern in cases of extreme skew. And then we cross-cross-cross check with another diagonal scan.

If that succeeds the finder pattern location is added to a list that tracks the number of times each location has been nearly-matched as a finder pattern. Each additional find is more evidence that the location is in fact a finder pattern center

Parameters:

stateCount - reading state module counts from horizontal scan

i - row where finder pattern may be found

j - end of possible finder pattern in row

pureBarcode - true if in "pure barcode" mode

Returns:

true if a finder pattern candidate was found this time