CameraX on Android Fragment in Kotlin with ImageAnalyzer

Rick_HK
3 min readJul 14, 2020
CameraX

CameraX is a relatively new Camera API in Android. Unlike the predecessors, CameraX is easy to use and requires less tweaking in order to adopt a Camera View in your application. Since, in the official sample code, Google made it a little buggy (for good intentions though) and they only implement it on Activity. So in this article, I’ll go over how to make implement CameraX using Fragment and mention some of the points we should be caution with.

1. Importing CameraX project in Gradle.

As of the day i write this article, the latest version of CameraX is “1.0.0-beta06”

def camerax_version = "1.0.0-beta06"
// CameraX core library using camera2 implementation
implementation "androidx.camera:camera-camera2:$camerax_version"
// CameraX Lifecycle Library
implementation "androidx.camera:camera-lifecycle:$camerax_version"
// CameraX View class
implementation "androidx.camera:camera-view:1.0.0-alpha13"

Also, remember to add the below block right below buildTypes in your module/app Gradle, in order for CameraX to use the Java 8 feature

compileOptions {
sourceCompatibility JavaVersion.VERSION_1_8
targetCompatibility JavaVersion.VERSION_1_8
}

2. Add the PreviewView to your fragment layout

After creating the fragment and stuffs, add the camerax previewview to the layout like this:

<androidx.camera.view.PreviewView
android:id="@+id/viewFinder"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>

I made the width and height both match_parent to fit my use case here

3. Initialising the Camera and PreviewView

There are a few things to note here.

i. ImageCapture

If you intend to capture image, you need to initialise the ImageCapture this is method.

imageCapture = ImageCapture.Builder().build()

ii. ImageAnalyzer

If you intend to capture image, you need to initialise the ImageAnalyzer this is method.

imageAnalyzer = ImageAnalysis.Builder().build().apply {
setAnalyzer(Executors.newSingleThreadExecutor(), CornerAnalyzer {
val
bitmap = viewFinder.bitmap
val img = Mat()
Utils.bitmapToMat(bitmap, img)
bitmap?.recycle()

val corner = processPicture(img)
// Image analysis here
})
}

iii. Bind everything to life cycle

Once you need all these helper objects, you need to bind it one-by-one to the camera object.

camera = cameraProvider.bindToLifecycle(this, cameraSelector, imageAnalyzer, preview, imageCapture)

Full function code:

val cameraProviderFuture = ProcessCameraProvider.getInstance(safeContext)
cameraProviderFuture.addListener(Runnable {
// Used to bind the lifecycle of cameras to the lifecycle owner
val cameraProvider: ProcessCameraProvider = cameraProviderFuture.get()

// Preview
preview = Preview.Builder().build()

imageCapture = ImageCapture.Builder().build()

imageAnalyzer = ImageAnalysis.Builder().build().apply {
setAnalyzer(Executors.newSingleThreadExecutor(), CornerAnalyzer {
val
bitmap = viewFinder.bitmap
val img = Mat()
Utils.bitmapToMat(bitmap, img)
bitmap?.recycle()

val corner = processPicture(img)
// Image analysis here
})
}
// Select back camera
val cameraSelector = CameraSelector.Builder().requireLensFacing(CameraSelector.LENS_FACING_BACK).build()

try {
// Unbind use cases before rebinding
cameraProvider.unbindAll()

// Bind use cases to camera
camera = cameraProvider.bindToLifecycle(this, cameraSelector, imageAnalyzer, preview, imageCapture)
preview?.setSurfaceProvider(viewFinder.createSurfaceProvider())
} catch (exc: Exception) {
Log.e(TAG, "Use case binding failed", exc)
}

}, ContextCompat.getMainExecutor(safeContext))

4. Setting a fixed Execution Thread

CameraX requires developer to set a thread for the execution. Set it in onViewCreated is a good place to choose.

cameraExecutor = Executors.newSingleThreadExecutor()

5. ImageAnalyzer

If you need to go image analysis, you need an image analyzer to provide you a bridge to get into the raw image data for every frame.

private class CornerAnalyzer(private val listener: CornersListener) : ImageAnalysis.Analyzer {

private fun ByteBuffer.toByteArray(): ByteArray {
rewind() // Rewind the buffer to zero
val data = ByteArray(remaining())
get(data) // Copy the buffer into a byte array
return data // Return the byte array
}

@SuppressLint("UnsafeExperimentalUsageError")
override fun analyze(imageProxy: ImageProxy) {
if (!isOffline) {
listener()
}
imageProxy.close()
}

}

One thing to note here is that it is NOT recommended to do analysis here, because converting ImageProxy to bitmap is too much work. I just analyze the image at the end of the listener, which is so much easier.

6. Full Code in Kotlin

Now without further ado, let’s check out the complete code:

That’s it.

Happy coding.

Let me know if you find better solution or approach in the comment section below. ;)

Find me at Twitter @rick3817

--

--

Rick_HK

Hi this is Rick from Hong Kong. I am a native iOS and Android mobile developer and also a tech enthusiast. Find me on Twitter https://twitter.com/rick3817