如何在安卓系统中将位图转换为nv21 byte[]数组

Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.image);

int width = bitmap.getWidth();
int height = bitmap.getHeight();

int[] argb = new int[width * height];
bitmap.getPixels(argb, 0, width, 0, 0, width, height);

byte[] yuv = new byte[width * height * 3 / 2];
encodeYUV420SP(yuv, argb, width, height);

private void encodeYUV420SP(byte[] yuv420sp, int[] argb, int width, int height) {
    final int frameSize = width * height;

    int yIndex = 0;
    int uvIndex = frameSize;

    int a, R, G, B, Y, U, V;
    int index = 0;
    for (int j = 0; j < height; j++) {
        for (int i = 0; i < width; i++) {
            a = (argb[index] & 0xff000000) >> 24; // alpha
            R = (argb[index] & 0xff0000) >> 16; // red
            G = (argb[index] & 0xff00) >> 8; // green
            B = (argb[index] & 0xff); // blue

            // RGB to YUV
            Y = ((66 * R + 129 * G + 25 * B + 128) >> 8) + 16;
            U = ((-38 * R - 74 * G + 112 * B + 128) >> 8) + 128;
            V = ((112 * R - 94 * G - 18 * B + 128) >> 8) + 128;

            // Clip rgb values to 0-255
            Y = Math.max(0, Math.min(Y, 255));
            U = Math.max(0, Math.min(U, 255));
            V = Math.max(0, Math.min(V, 255));

            // Write YUV values to byte array
            yuv420sp[yIndex++] = (byte) Y;
            if (j % 2 == 0 && index % 2 == 0) {
                yuv420sp[uvIndex++] = (byte) U;
                yuv420sp[uvIndex++] = (byte) V;
            }

            index++;
        }
    }
}