16進数文字列から画像に変換する方法（Kotlin）

fun hextoBitmap(file: String): Bitmap {
        val openfile = assets.open(file)
        var imagetext = ""
        try {
            val inst = InputStreamReader(openfile)
            val br = BufferedReader(inst)
            var line = br.readLine()
            while (line != null) {
                imagetext += line
                line = br.readLine()
            }
            inst.close()
            br.close()
        }catch (e:IOException) {
            Log.e("IOException", e.toString())
        }

        val bytes = mutableListOf<Byte>()
        for(index in 1..imagetext.length/2) {
            val byte = Integer.parseInt(imagetext.substring((index - 1) * 2,index * 2),16)
            bytes.add(byte.toByte())
        }
        println(bytes)

        val byteArray = bytes.toByteArray()

        val bitmap = BitmapFactory.decodeByteArray(bytearray, 0, byteArray.size)

        return bitmap
    }