如何在Kotlin中将Bitmap中的白色边框/背景删除？

val mutableBitmap = bitmap.copy(Bitmap.Config.ARGB_8888, true)

for (x in 0 until mutableBitmap.width) {
    for (y in 0 until mutableBitmap.height) {
        val pixel = mutableBitmap.getPixel(x, y)
        if (Color.alpha(pixel) == 255 && Color.red(pixel) == 255 && Color.green(pixel) == 255 && Color.blue(pixel) == 255) {
            mutableBitmap.setPixel(x, y, Color.TRANSPARENT)
        }
    }
}

imageView.setImageBitmap(mutableBitmap)