OcrTextDetector.kt

class TextDetector {

   private val detector = FirebaseVision.getInstance().visionTextDetector
   private val detectionOutput = PublishProcessor.create<FirebaseVisionText>()
   private val frameInput = PublishProcessor.create<Bitmap>()

   init {
       frameInput.map { it.toFirebaseVisionImage() }
               .flatMap(::detect)
               .subscribe(detectionOutput)
   }

   fun processImage(image: Bitmap) {
       frameInput.offer(image)
   }

   fun observeDetections(): Flowable<FirebaseVisionText> = detectionOutput

   fun detect(visionImage: FirebaseVisionImage): Flowable<FirebaseVisionText> =
           detector.detectInImage(visionImage).toFlowable()
}

fun Bitmap.toFirebaseVisionImage(): FirebaseVisionImage = FirebaseVisionImage.fromBitmap(this)