Question

Im trying to use ZXing library to develop a Java project for decoding a QR code. However, some of the image containing QR code can not be decoded by running my project, but these are working fine with Online ZXing decoder. I am just curious does the ZXing released version is the same as they are using for Online decoder? or they have tweaked the online version. I’m pulling my hair because of this confusion.

public class Validator implements IValidator {
    private static Logger logger = Logger.getLogger(Validator.class);
    private BufferedImage currentImage;
    private String resultText;
    private float moduleSize;
    private ResultPoint[] patternCenters;
    private int blockSizePower;

    public Validator(BufferedImage imageFile) {
        this.currentImage = imageFile;
        setLuminanceThreshold(3); //default value used by validator
    }

    public Validator(File imageFile) {
        // take input image file and store in a BufferedImage variable
        try {
            currentImage = ImageIO.read(imageFile);
        } catch (IOException e) {
            logger.error("Image cannot be opened. There is no such image file. ", e);
        }
    }


    /**
     * <p>Validating the QR code</p>
     *
     * @return true if the QR code can be decoded
     */
    @Override
    public boolean validateQRCode() {
        return validateQRCode(null);
    }

    public boolean validateQRCode(Hashtable outValues) {
        return validateQRCode(outValues, true);
    }

    // if localLuminanceCheck == true then call HybridBinarizer, otherwise call GlobalHistogramBinarizer  
    public boolean validateQRCode(Hashtable outValues, boolean localLuminanceCheck)
    {
        return validateQRCode(outValues, true, false);
    }

    public boolean validateQRCode(Hashtable outValues, boolean localLuminanceCheck, boolean scale) {
        if (scale)
        {
            try {
                this.currentImage = Thumbnails.of(currentImage).size(275, 275).asBufferedImage();

            } catch (IOException e) {
                logger.error("Image cannot be scaled. ", e);
            }
        }

        // finding luminance of the image
        LuminanceSource lumSource = new BufferedImageLuminanceSource(currentImage);

        Binarizer qrHB;
        if (!localLuminanceCheck) {
            qrHB = new GlobalHistogramBinarizer(lumSource);
        } else {
            // creating binary bitmap from Black-White image
            qrHB = new HybridBinarizer(lumSource);
            ((HybridBinarizer) qrHB).setBLOCK_SIZE_POWER(blockSizePower);
        }
        BinaryBitmap bitmap = new BinaryBitmap(qrHB);

        try {
            currentImage = MatrixToImageWriter.toBufferedImage(bitmap.getBlackMatrix());
        } catch (NotFoundException e) {
            logger.error("cannot find any bit matrix.", e);
        }

        Hashtable<DecodeHintType, Object> hint = new Hashtable<DecodeHintType, Object>();
        hint.put(DecodeHintType.TRY_HARDER, BarcodeFormat.QR_CODE);

        QRCodeReader QRreader = new QRCodeReader();

        try {
            // decodes the QR code
            Result result = QRreader.decode(bitmap, hint);

            resultText = result.getText();
            return true;
        } catch (NotFoundException e) {
            logger.info("cannot detect any QR code (no enough finder patterns).");
            return false;
        } catch (ChecksumException e) {
            logger.info("cannot recover the QR code. Too much data errors.");
            return false;
        } catch (FormatException e) {
            logger.info("QR code cannot be decoded.");
            return false;
        } catch (FinderPatternNotFoundException e) {
            // if no Finder Pattern has been found, it may be the color of
            // QR is inverted. So we invert the QR and try one more time

            Binarizer invertHB;
            if (!localLuminanceCheck) {
                invertHB = new GlobalHistogramBinarizer(lumSource);
            } else {
                invertHB = new HybridBinarizer(lumSource);
                ((HybridBinarizer) invertHB).setBLOCK_SIZE_POWER(blockSizePower);
            }

            // get the inverted Black-White matrix
            BitMatrix invertBlackMatrix = null;
            try {
                invertBlackMatrix = invertHB.getBlackMatrix();
            } catch (NotFoundException e1) {
                logger.error(e1);
            }

            int invertWidth = currentImage.getWidth();
            int invertHeight = currentImage.getHeight();

            // flip each bit in the inverted BitMatrix
            for (int x = 0; x < invertWidth; x++) {
                for (int y = 0; y < invertHeight; y++) {
                    invertBlackMatrix.flip(x, y);
                }
            }

            currentImage = MatrixToImageWriter.toBufferedImage(invertBlackMatrix);

            // get luminance source from inverted image
            lumSource = new BufferedImageLuminanceSource(currentImage);

            Binarizer afterInvertHB;
            if (!localLuminanceCheck) {
                afterInvertHB = new GlobalHistogramBinarizer(lumSource);

            } else {
                // creating binary bitmap from Black-White image
                afterInvertHB = new HybridBinarizer(lumSource);
                ((HybridBinarizer) afterInvertHB).setBLOCK_SIZE_POWER(blockSizePower);
            }
            BinaryBitmap invertBitMap = new BinaryBitmap(afterInvertHB);

            // decoding inverted QR
            QRCodeReader invertQRreader = new QRCodeReader();

            try {
                Result invertResult = invertQRreader.decode(invertBitMap, hint);

                resultText = invertResult.getText();

                System.out.println("Out put data is: " + resultText);

                return true;
            } catch (NotFoundException e1) {
                logger.info("cannot detect any QR code (no enough finder patterns).");
                return false;
            } catch (ChecksumException e1) {
                logger.info("cannot recover the QR code. Too much data errors.");
                return false;
            } catch (FormatException e1) {
                logger.info("QR code cannot be decoded.");
                return false;
            } catch (FinderPatternNotFoundException e1) {
                logger.info("Cannot confirm where all three Finder Patterns are! ");
                return false;
            } catch (Exception e1) {
                logger.error(e1);
                return false;
            }
        } catch (Exception e) {
            logger.error(e);
            return false;
        }
    }

}

Answer 1

It’s not different, it’s probably that you are not using TRY_HARDER mode, or are not trying both binarizers. The online version will do those things.