android 把图变成灰色

 public static final Bitmap grey(Bitmap bitmap) {
  int width = bitmap.getWidth();
  int height = bitmap.getHeight();
  
  Bitmap faceIconGreyBitmap = Bitmap
    .createBitmap(width, height, Bitmap.Config.ARGB_8888);
  
  Canvas canvas = new Canvas(faceIconGreyBitmap);
  Paint paint = new Paint();
  ColorMatrix colorMatrix = new ColorMatrix();
  colorMatrix.setSaturation(0);
  ColorMatrixColorFilter colorMatrixFilter = new ColorMatrixColorFilter(
    colorMatrix);
  paint.setColorFilter(colorMatrixFilter);
  canvas.drawBitmap(bitmap, 0, 0, paint);
  return faceIconGreyBitmap;
 }