Android：裁剪面部并优化边缘

Question

我正在创建人脸转换应用程序。我能够检测到一张脸并在其中画一个椭圆形。现在我遇到了一个问题：裁剪出脸。我正在为此使用Vision API。

这是我的代码。它能够检测到人脸并在其上画一个圆：

 private class SaveImageAsync extends AsyncTask<Bitmap, Void, Void> {

        File file;
        Bitmap bitmap;

        @Override
        protected Void doInBackground(Bitmap... bitmaps) {
            bitmap = bitmaps[0];
            Bitmap faceBitmap;

            //Bitmap test = BitmapFactory.decodeResource(getResources(), R.drawable.traditional_f_filter_x);
            Bitmap mutableBitmap = bitmap.copy(Bitmap.Config.ARGB_8888, true);
            Bitmap tempBitmap = Bitmap.createBitmap(mutableBitmap.getWidth(), mutableBitmap.getHeight(), Bitmap.Config.RGB_565);

            Paint paint = new Paint();
            paint.setStrokeWidth(5);
            paint.setColor(Color.RED);
            paint.setStyle(Paint.Style.STROKE);

            Canvas canvas = new Canvas(tempBitmap);
            canvas.drawBitmap(mutableBitmap, 0, 0 , null);

            FaceDetector detector = new FaceDetector.Builder(getApplicationContext()).setTrackingEnabled(false).build();
            if (!detector.isOperational()) {
                Toast.makeText(getApplicationContext(), "ERROR", Toast.LENGTH_LONG).show();
            }

            Frame frame = new Frame.Builder().setBitmap(mutableBitmap).build();
            try {
                SparseArray<Face> faces = detector.detect(frame);
                Face face = faces.valueAt(0);
                int left = (int) (face.getPosition().x);
                int top = (int) (face.getPosition().y);
                int right = (int) (face.getPosition().x + face.getWidth());
                int bottom = (int) (face.getPosition().y + face.getHeight());
                canvas.drawOval(new RectF(left, top, right, bottom), paint);
                faceBitmap = Bitmap.createBitmap(tempBitmap, left, top, right - left, bottom - top);
                file = getOutputMediaFile(getApplicationContext());
                FilterSystem.selectedImage = faceBitmap;
            } catch (Exception e) {
                faceBitmap = null;
                Log.e("ERROR", "CANNOT DETECT FACE " +e.getMessage());
            }
            try {
                FileOutputStream fos = new FileOutputStream(file);
                faceBitmap.compress(Bitmap.CompressFormat.JPEG, 100, fos);
            } catch (Exception e) {}
            return null;
        }

        @Override
        protected void onPostExecute(Void aVoid) {
            super.onPostExecute(aVoid);
            progressBar.setVisibility(View.INVISIBLE);
            Toast.makeText(getApplicationContext(), "DONE PROCESSING", Toast.LENGTH_LONG).show();
        }
    }

现在，我可以轻松地从整个图像中裁剪出包含面部的圆圈，然后换出图像，但这不是我想要的。我只想要脸部特征（眼睛，鼻子，嘴巴），并能够过滤它们，因此颜色也能匹配。我该如何实现？我已经看过OpenCV，但不知道如何从这里继续。还有其他选择吗？