Unable to read QR using Zxing

Question

I am using zxing library to generate and decode the QR codes. I my application I am generating QR code dynamically and sending the file containing QR by fax API. If I get this fax message from the api and decode it, Qr code is read successfully, but when I send a scanned copy of this file by fax and then receive and read it I am unable to do that. But if I try to read this file using my mobile Qr application it properly reads the Qr code. I am unable to find a solution how to read this file.

Methods used for encoding:

public static System.Drawing.Image GenerateJSONQrCode(QRJsonFax model)
    {
        var jsonString = JsonConvert.SerializeObject(model);
        //encrypt json string
        jsonString = Hugo.BLL.Utilities.EncryptionHelper.EncryptQR(jsonString, FaxSetting.IsUseHashing);
        var bw = new ZXing.BarcodeWriter();
        var encOptions = new ZXing.Common.EncodingOptions() { Width = 200, Height = 200, Margin = 0 };
        bw.Options = encOptions;
        bw.Format = ZXing.BarcodeFormat.QR_CODE;
        var image = new Bitmap(bw.Write(Compress(jsonString)));
        return image;
    }

private static string Compress(string text)
    {
        byte[] buffer = Encoding.UTF8.GetBytes(text);
        var ms = new MemoryStream();
        using (var zip = new GZipStream(ms, CompressionMode.Compress, true))
        {
            zip.Write(buffer, 0, buffer.Length);
        }

        ms.Position = 0;
        byte[] compressed = new byte[ms.Length];
        ms.Read(compressed, 0, compressed.Length);

        byte[] gzBuffer = new byte[compressed.Length + 4];
        System.Buffer.BlockCopy(compressed, 0, gzBuffer, 4, compressed.Length);
        System.Buffer.BlockCopy(BitConverter.GetBytes(buffer.Length), 0, gzBuffer, 0, 4);
        return Convert.ToBase64String(gzBuffer);
    }

Methods used for encoding and decoding

 public static FaxReceiver.QrFinder DecodeQrCode(string imagePathToDecode)
    {
        long userId = 0;
            Bitmap bitmapImage = (Bitmap)Image.FromFile(imagePathToDecode);
            ZXing.BarcodeReader barcodeReader = new BarcodeReader() { AutoRotate = true, TryHarder = true }; ;
            Result decode = barcodeReader.Decode(bitmapImage);
            var scanResult = string.Empty;
            if (decode != null)
            {
              scanResult= Decompress(decode.Text);
            }

        if (!string.IsNullOrWhiteSpace(scanResult))
            {
                //decrypt Qr received
                var decryptedString = DecryptionHelper.Decrypt(scanResult, FaxSetting.IsUseHashing);

                //deserialize JSON received
                var resultJson = JsonConvert.DeserializeObject<QRJsonFax>(decryptedString);
                if (resultJson != null)
                {
                    long.TryParse(resultJson.UserID.ToString(), out userId);
                    return new QrFinder()
                    {
                        FilePath = imagePathToDecode,
                        UserId = userId,
                        PageNo = 0,
                        DataSourceID = resultJson.DataSourceID,
                        InboundFaxTypeID = resultJson.InboundFaxTypeID
                    };
                }
            }
        return null;
    }

   private static string Decompress(string compressedText)
    {
        byte[] gzBuffer = Convert.FromBase64String(compressedText);
        using (var ms = new MemoryStream())
        {
            int msgLength = BitConverter.ToInt32(gzBuffer, 0);
            ms.Write(gzBuffer, 4, gzBuffer.Length - 4);

            byte[] buffer = new byte[msgLength];

            ms.Position = 0;
            using (var zip = new GZipStream(ms, CompressionMode.Decompress))
            {
                zip.Read(buffer, 0, buffer.Length);
            }

            return Encoding.UTF8.GetString(buffer);
        }
    }

File containing Qr code

Answer 1

The problem is that the QR Decoder is getting confused by the gaps between the pixels in your faxed image. If we zoom into a corner of it, this is what we see.

The scanner is looking for solid black squares to identify the QR code.

If we shrink the image by 50%, it becomes readable.

See for yourself at http://zxing.org/w/decode?u=http%3A%2F%2Fi.stack.imgur.com%2FSCYsd.png

I would suggest that after receiving the faxed image, you should either shrink it, or apply a filter to ensure that the QR codes are solid black. You could also look at sending it at a smaller resolution to see if that helps.