Difficulty with Close QR Codes

[mtrewartha]

I seem to be having some weird inconsistency with detecting QR codes... any time my particular QR code (which is rather small) gets less than ~5 inches from the camera, the detector doesn't seem to pick up the QR code despite the camera still being in focus. Here's an example screenshot, where I should be seeing a green box around the QR code, but don't. Any idea what's going on?

[seeingwithsound]

The little squares on your QR code photo appear distorted. Did you try a higher quality QR code print of the same dimensions? I can imagine that the QR code detection algorithms have problems with the jagged edges or whatever when close enough to be within the camera resolution.

[mtrewartha]

I noticed that right after posting... I'll try a higher resolution print and see what happens. However, I still generally have issues with situations I wouldn't think to be troublesome. Here's another screenshot of a QR code on my screen that's being picked up occasionally, but nowhere near as easily as you'd think. I've also noticed that moving the camera just a tad seems to help detection and often times, when I stop moving, the QR code is lost. Right now, I'm using 30 FPS and a max gap size of 30 frames, but I notice the behavior with all sorts of settings.

[seeingwithsound]

Strange indeed, I do not see a problem with your screenshot. I can only guess, but it might be that your code is reentrant such that at 30fps a next QR code recognition starts before the previous one has finished processing, which can give all sorts of effects. Be sure to disable recognition until the previous one has finished with a result (where "not recognized" also counts as a result).

[mtrewartha]

I'm not quite sure I understand... I don't have any home-rolled code that controls QR code recognition, I'm just using the BarcodeDetector and MultiProcessor stuff that's part of the library. Here's a quick idea of what I'm doing.

First, I create a BarcodeDetector:

val qrCodeDetector by lazy {
    BarcodeDetector.Builder(this)
            .setBarcodeFormats(Barcode.QR_CODE)
            .build()
}

Then I create a MultiProcessor and give it to the above qrCodeDetector:

val qrCodeTracker = MultiProcessor.Builder<Barcode>(QrCodeTrackerFactory())
        .setMaxGapFrames(MISSING_FRAME_MAX)
        .build()
qrCodeDetector.setProcessor(qrCodeTracker)

Then I create a CameraSource using the processor:

CameraSource.Builder(this, qrCodeDetector)
        .setAutoFocusEnabled(true)
        .setFacing(CameraSource.CAMERA_FACING_BACK)
        .setRequestedFps(CAMERA_FPS)
        .setRequestedPreviewSize(width, height)
        .build()

[pchx-zz]

The QR code looks fine, but getting too close to it will cause trouble (as you've noticed).