从资源文件目录获取图片：

Drawable drawable = ContextCompat.getDrawable(this, R.mipmap.ic_launcher);
drawable.getBounds(); // 获取Drawable的大小范围


将Drawable转换成Bitmap

        Drawable drawable = ContextCompat.getDrawable(this, R.mipmap.ic_launcher);
        drawable.setBounds(0,0, drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight());
        Bitmap bitmap = Bitmap.createBitmap(drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight(), Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(bitmap);
        drawable.draw(canvas);

        iv.setImageBitmap(bitmap); //将Drawable转换成的Bitmap设置到ImageView.

获取设置在ImageView上的图片 ：

 Bitmap bitmap = ((BitmapDrawable)imageView.getDrawable()).getBitmap();

将资源文件中的图片转成Bitmap有第二种方法：

      imageView.setImageResource(R.mipmap.ic_launcher);
      Bitmap bitmap = ((BitmapDrawable)imageView.getDrawable()).getBitmap();

二  ：  将Bitmap转为Drawable的方法：

        BitmapDrawable bitmapDrawable = new BitmapDrawable(mContext.getResources(), bitmap);
参考：ImageView.setImageBitmap()　
获取ImageView上的图片的方法  （CircleImageView）
    private Bitmap getBitmapFromDrawable(Drawable drawable) {
        if (drawable == null) {
            return null;
        if (drawable instanceof BitmapDrawable) {
            return ((BitmapDrawable) drawable).getBitmap();
        }else if (drawable instanceof GlideBitmapDrawable) {
            GlideBitmapDrawable glideBitmapDrawable = (GlideBitmapDrawable) drawable;
            return glideBitmapDrawable.getBitmap();
        }else if (drawable instanceof SquaringDrawable){
     try {
            Bitmap bitmap;
            if (drawable instanceof ColorDrawable) {
                bitmap = Bitmap.createBitmap(COLORDRAWABLE_DIMENSION, COLORDRAWABLE_DIMENSION, BITMAP_CONFIG);
            } else {
                bitmap = Bitmap.createBitmap(drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight(), BITMAP_CONFIG);
            Canvas canvas = new Canvas(bitmap);
            drawable.setBounds(0, 0, canvas.getWidth(), canvas.getHeight());
            drawable.draw(canvas);
            return bitmap;
        } catch (Exception e) {
            e.printStackTrace();
            return null;