Class Detector

  • Direct Known Subclasses:
    MultiDetector

    public class Detector
    extends java.lang.Object

    Encapsulates logic that can detect a QR Code in an image, even if the QR Code is rotated or skewed, or partially obscured.

    • Constructor Detail

      • Detector

        public Detector​(BitMatrix image)
    • Method Detail

      • getImage

        protected final BitMatrix getImage()
      • computeDimension

        private static int computeDimension​(ResultPoint topLeft,
                                            ResultPoint topRight,
                                            ResultPoint bottomLeft,
                                            float moduleSize)
                                     throws NotFoundException

        Computes the dimension (number of modules on a size) of the QR Code based on the position of the finder patterns and estimated module size.

        Throws:
        NotFoundException
      • calculateModuleSize

        protected final float calculateModuleSize​(ResultPoint topLeft,
                                                  ResultPoint topRight,
                                                  ResultPoint bottomLeft)

        Computes an average estimated module size based on estimated derived from the positions of the three finder patterns.

        Parameters:
        topLeft - detected top-left finder pattern center
        topRight - detected top-right finder pattern center
        bottomLeft - detected bottom-left finder pattern center
        Returns:
        estimated module size
      • sizeOfBlackWhiteBlackRunBothWays

        private float sizeOfBlackWhiteBlackRunBothWays​(int fromX,
                                                       int fromY,
                                                       int toX,
                                                       int toY)
        See sizeOfBlackWhiteBlackRun(int, int, int, int); computes the total width of a finder pattern by looking for a black-white-black run from the center in the direction of another point (another finder pattern center), and in the opposite direction too.
      • sizeOfBlackWhiteBlackRun

        private float sizeOfBlackWhiteBlackRun​(int fromX,
                                               int fromY,
                                               int toX,
                                               int toY)

        This method traces a line from a point in the image, in the direction towards another point. It begins in a black region, and keeps going until it finds white, then black, then white again. It reports the distance from the start to this point.

        This is used when figuring out how wide a finder pattern is, when the finder pattern may be skewed or rotated.

      • findAlignmentInRegion

        protected final AlignmentPattern findAlignmentInRegion​(float overallEstModuleSize,
                                                               int estAlignmentX,
                                                               int estAlignmentY,
                                                               float allowanceFactor)
                                                        throws NotFoundException

        Attempts to locate an alignment pattern in a limited region of the image, which is guessed to contain it. This method uses AlignmentPattern.

        Parameters:
        overallEstModuleSize - estimated module size so far
        estAlignmentX - x coordinate of center of area probably containing alignment pattern
        estAlignmentY - y coordinate of above
        allowanceFactor - number of pixels in all directions to search from the center
        Returns:
        AlignmentPattern if found, or null otherwise
        Throws:
        NotFoundException - if an unexpected error occurs during detection