MainActivity.kt

class MainActivity : AppCompatActivity() {

    private lateinit var renderScript: RenderScript
    private lateinit var yuvToRGB: ScriptIntrinsicYuvToRGB
    private var yuvDataLength: Int = 0
    private lateinit var allocationIn: Allocation
    private lateinit var allocationOut: Allocation
    private lateinit var bitmapOut: Bitmap

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        Fritz.configure(this)
         cameraView.addFrameProcessor { frame ->
            if (yuvDataLength == 0) {
                //Run this only once
                initializeData()
            }
            //Camera Preview returns NV21, so convert it to Bitmap :
            //https://stackoverflow.com/a/43551798/5471095
            allocationIn.copyFrom(frame.data) //Take the NV21 format
            yuvToRGB.forEach(allocationOut)  //Convert it to Bitmap readable format
            allocationOut.copyTo(bitmapOut)   //Set it to the empty Bitmap created earlier
        }
    }
  
  private fun initializeData(){
        yuvDataLength = cameraView.previewSize?.height!! * cameraView.previewSize?.width!! * 3 / 2
        renderScript = RenderScript.create(baseContext)
        yuvToRGB = ScriptIntrinsicYuvToRGB.create(renderScript, Element.U8_4(renderScript))
        allocationIn = Allocation.createSized(renderScript, Element.U8(renderScript), yuvDataLength)
        bitmapOut = Bitmap.createBitmap(cameraView.previewSize?.width!!, cameraView.previewSize?.height!!, Bitmap.Config.ARGB_8888)
        allocationOut = Allocation.createFromBitmap(renderScript, bitmapOut)
        yuvToRGB.setInput(allocationIn)
    }
}