build.gradle

renderscriptTargetApi 18
renderscriptSupportModeEnabled true

//#######################################################################################

object BlurBuilder {

    private const val BITMAP_SCALE = 0.6f
    private const val BLUR_RADIUS = 15f

    fun makeBlur(context: Context, image: Bitmap): Bitmap {
        val width = Math.round(image.width * BITMAP_SCALE)
        val height = Math.round(image.height * BITMAP_SCALE)

        val inputBitmap = Bitmap.createScaledBitmap(image, width, height, false)
        val outputBitmap = Bitmap.createBitmap(inputBitmap)

        val rs = RenderScript.create(context)

        val intrinsicBlur = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs))
        val tmpIn = Allocation.createFromBitmap(rs, inputBitmap)
        val tmpOut = Allocation.createFromBitmap(rs, outputBitmap)

        intrinsicBlur.setRadius(BLUR_RADIUS)
        intrinsicBlur.setInput(tmpIn)
        intrinsicBlur.forEach(tmpOut)
        tmpOut.copyTo(outputBitmap)

        return outputBitmap
    }
}