Unable to read image from camera in java/kotlin

Android/Java
1

repo

I’m using the org.bytedeco:opencv-platform maven port to use opencv in kotlin.
Main.kt:


fun main() = runBlocking {
    // Load native libraries, mainly opencv
    Loader.load(opencv_java::class.java)

    println("Attempting a connection to the robot")
    val client = RobotClient()

    // Camera properties
    val ballCamProps = MatOfInt(
        Videoio.CAP_PROP_FRAME_WIDTH, 480,
        Videoio.CAP_PROP_FRAME_HEIGHT, 640
    )
    
    println("Creating trackers")
    val ballCam = BallTracker(VideoCapture(-1, Videoio.CAP_ANY, ballCamProps), client)
    
    println("Running trackers")
    ballCam.runAsync()
   
    println("Starting video stream")
    while(true) {
        if(!ballCam.currentFrame.empty()){
            ballCam.imstream(ballCam.currentFrame);
        } else {
            throw Exception("Current frame is empty")
        }
    }

BallTracker.kt:

class BallTracker(cap: VideoCapture, net: RobotClient): AsyncPipeline {
    var currentFrame = Mat()
    override val client = net

    private val mutex = Mutex()
    private val _capture = cap

    private fun process(img: Mat, range: Pair<Scalar, Scalar>): Mat {
        ...
    }

    private fun track(threshed: Mat): Map<String, Double> {
        ...
    }

    override fun runAsync() = GlobalScope.async {
        val blue = Pair<Scalar, Scalar>(
            Scalar(92.0, 139.0, 76.0),
            Scalar(115.0, 210.0, 175.0)
        )
        val red = Pair<Scalar, Scalar>(
            Scalar(165.0, 92.0, 52.0),
            Scalar(175.0, 218.0, 213.0)
        )

        while(_capture.isOpened) {
            mutex.withLock {
                if(_capture.read(currentFrame)) {
                    val processed = process(currentFrame, blue)
                    val trackerData = track(processed)
                } else {
                    throw Exception("Unable to read frame from camera")
                }
            }
        }
        throw Exception("Unable to open camera")
    }

    suspend fun imstream(img: Mat) {
        mutex.withLock {
            HighGui.imshow("Ball cam", img)
        }
    }
}

I’m not familer with opencv in java and in c++ I’d normally use the << operator to read from a camera

2

unfortunately, we cant help much with bytedeco.
it’s a 3rd party effort, they made a totally different api,
noone knows about it here

3

If I were using the actual opencv java bindings though what do you think would be the cause of this?