Scan QRcode with inverted colors using Vision API

Question

After struggling a few hours on making my app detect this QRCode:

I realized that the problem was the in the QRCode appearance. After inverting the colors, the detection was working perfectly..

Is there a way to make Vision API detect the first QRCode? I tried to enable all symbologies but it did not work. I guess it is possible because the app QR Code Reader detects it.

Just to clarify, I tried to scan the second QR code with the blue color and it works perfectly as well, there is no special need for a black QRCode. — Louis, Nov 16 '17 at 14:47

score 4 · Accepted Answer · answered Apr 11 '18 at 05:59

I improved googles example app "barcode-reader" to detect both inverted colored barcodes and regular ones.

here is a link to googles example app:

https://github.com/googlesamples/android-vision/tree/master/visionSamples/barcode-reader

I did so by editing "CameraSource" class, package: "com.google.android.gms.samples.vision.barcodereader.ui.camera".

I added a parameter: private boolean isInverted = false;

and changed function void setNextFrame(byte[] data, Camera camera):

void setNextFrame(byte[] data, Camera camera) {
            synchronized (mLock) {
                if (mPendingFrameData != null) {
                    camera.addCallbackBuffer(mPendingFrameData.array());
                    mPendingFrameData = null;
                }

                if (!mBytesToByteBuffer.containsKey(data)) {
                    Log.d(TAG,
                            "Skipping frame.  Could not find ByteBuffer associated with the image " +
                                    "data from the camera.");
                    return;
                }

                mPendingTimeMillis = SystemClock.elapsedRealtime() - mStartTimeMillis;
                mPendingFrameId++;
                if (!isInverted){
                    for (int y = 0; y < data.length; y++) {
                        data[y] = (byte) ~data[y];
                    }
                    isInverted = true;
                } else {
                    isInverted = false;
                }
                mPendingFrameData = mBytesToByteBuffer.get(data);

                // Notify the processor thread if it is waiting on the next frame (see below).
                mLock.notifyAll();
            }
        }

score 1 · Answer 2 · edited Jun 20 '20 at 09:12

I think this is still an open issue, please see link for details. One workaround for this as stated by a developer:

Right, the barcode API generally doesn't support color-inverted codes. There's no parameter or option to control this at the moment. Though some APIs support them, I don't believe it's a common feature.

For a workaround, you could preprocess the colors in the bitmap before passing them to the barcode API (perhaps inverting colors on alternate frames).

Hope this helps.

Scan QRcode with inverted colors using Vision API

2 Answers2

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