扫描PDF并转换为缓冲图像以解码QR时Zxing格式异常

Question

I'm having problem with getting continuous successful QR decoding after PDF conversion. I keep getting,

"Exception in thread "main" com.google.zxing.FormatException."

My conversion attempts were done in: PDFBox

public static BufferedImage convertPDFtoBufferedImageType2(String PDFPath) throws IOException{

    PDDocument document = null;
    try {

        document = PDDocument.load(PDFPath);
        PDPage firstPage = (PDPage) document.getDocumentCatalog().getAllPages().get(0);
        return firstPage.convertToImage();

    } catch (IOException ex) {
        Logger.getLogger(PDF_Utility.class.getName()).log(Level.SEVERE, null, ex);
        return null;
    } finally {
        if(document != null)
            document.close();
    }
}

Second Attempt with ghost4j

public static BufferedImage convertPDFtoBufferedImage(String PDFPath) throws IOException, RendererException, DocumentException{

    System.setProperty("jna.library.path", "C:\\Program Files\\gs\\gs9.16\\bin\\");

    PDFDocument document = new PDFDocument();
    document.load(new File(PDFPath));
    SimpleRenderer renderer = new SimpleRenderer();
    renderer.setResolution(300);
    List<Image> imgs = renderer.render(document);
    Image im = imgs.get(0);

    BufferedImage bi = new BufferedImage
        (im.getWidth(null),im.getHeight(null),BufferedImage.TYPE_INT_RGB);
    Graphics bg = bi.getGraphics();
    bg.drawImage(im, 0, 0, null);
    bg.dispose();
    return bi;
}

My QR Decoder is:

public static String readQRCode(BufferedImage image, String charset, Map hintMap) 
                throws FileNotFoundException, IOException, NotFoundException, ChecksumException, FormatException {
        Result qrCodeResult = null;
        BinaryBitmap binaryBitmap = new BinaryBitmap(
                        new HybridBinarizer(new BufferedImageLuminanceSource(image)));
        try{
            qrCodeResult = new com.google.zxing.qrcode.QRCodeReader().decode(binaryBitmap,hintMap);
        }catch(NotFoundException | FormatException e){ //attempt without hints
            qrCodeResult = new com.google.zxing.qrcode.QRCodeReader().decode(binaryBitmap);
        }
        return qrCodeResult.getText();
}

And the reason why I called decode twice was because sometimes the "try harder"

hintMap.put(DecodeHintType.TRY_HARDER, Boolean.TRUE);

actually didn't catch the QR code, but the default did. Anyways, these code snippets do catch most of my QR scans from a pile of documents, but there are times where it does not catch it at all. I even attempted to write it out as an image and then re-read it in:

ImageIO.write((RenderedImage) im, "png", new File("/path/to/my/img.png"));

Interestingly, http://zxing.org/w/decode.jspx does decode that output image, but my code couldn't. I also tried different charset: CHAR_SET = "UTF-8"; and CHAR_SET = "ISO-8859-1";

By getting Format Exceptions, the code was found, but "did not conform to the barcode's format rules. This could have been due to a mis-detection."

Apology for the messy code, but those attempts have gained majority of successful scans. 9/10 rate? Interestingly, sometimes another scanned copy of the same doc worked. Any help/advice/crazy voodoo combination is appreciated! Thanks!

EDIT: I got a sample (after whiting out the contents around. The real image has contents! Zxing website was able to catch this QR code too (with and without contents! (My program already ignored the other 1Ds at this same format and those with contents).

Answer 1

@Tilman Hausherr pointed out for the PDFBox default rendering size as low so I changed the default to 300dpi as he suggested. Overall, it worked for my case but definitely slowed down the speed. Will need to tweak my algorithm to run both a fast and this slower one as a backup.

return firstPage.convertToImage(BufferedImage.TYPE_4BYTE_ABGR, 300);

EDIT: Increased the success rate of catching barcodes, but did not successfully catch all. Increasing the dpi does not help.