Capture Frame using JavaCamera2View

Issue

I am using OpenCV in Android and I have the JavaCamera2View which is an implementation of CameraBridgeViewBase. I can display the preview with no problems. But I also want to capture an image on a button press and this is where I am having issues. I have looked around and saw that in some SO questions it is suggested to use JavaCameraView.takePicture but I think that function is not present in the second iteration. What I tried instead is the following code:

class MainViewModel(application: Application) : AndroidViewModel(application),
    CameraBridgeViewBase.CvCameraViewListener2 {
    ...
    private var currentFrame: Mat? = null
    ...
    override fun onCameraFrame(inputFrame: CameraBridgeViewBase.CvCameraViewFrame?): Mat {
        inputFrame?.let {
            currentFrame = it.rgba()
            return currentFrame!!

        }
        return Mat().setTo(Scalar.all(0.0))
    }
    ...
    fun captureFrame() {
        currentFrame?.let {
            if (it.empty()) {
                Log.e(tag, "FRAME IS EMPTY")
                return
            }
            val directoryString =
                getApplication<Application>().getExternalFilesDir(Environment.DIRECTORY_PICTURES)!!.absolutePath
            val directory = File(directoryString, "calibration")
            if (!directory.mkdirs() && !directory.isDirectory) {
                Log.e(tag, "Failed to create image directory")
                return
            }
            val imageFile =
                File(directory, dateFormat.format(Date()) + _distance.value.toString() + ".jpg")

            val success = Imgcodecs.imwrite(imageFile.path, it)
            if (success) {
                Log.d(tag, "image saved")
            } else {
                Log.d(tag, "failed to save")
            }
        }

I call the captureFrame method when the user taps on a button in UI, and the problem here is that I get FRAME IS EMPTY response way too much. I can save the picture in around only 30% of the clicks. The camera is working with 15 fps so is it because when the user clicks to capture a frame, the currentFrame is in the process of being written? Or is there any other reason that can cause this? Is there a better way to capture a frame? Should I implement saving the image into the JavaCamera2View code myself? This feels like not a very trivial task, though.

Solution

In the end, I came up with another architecture where I have a boolean shouldSave which is updated from the UI. I check this flag within the onCameraFrame callback and if it is true, I save the frame and set it to false. This approach has the drawback of saving the next frame after the flag is set, but works 100% of the time nonetheless.

Answered By - mcy