读取SD卡图片 转化Bitmap

public static Bitmap convertToBitmap(String path, int w, int h) {
         BitmapFactory.Options opts = new BitmapFactory.Options();
     // 设置为ture只获取图片大小
       opts.inJustDecodeBounds = true;
        opts.inPreferredConfig = Bitmap.Config.ARGB_8888;
        // 返回为空
       BitmapFactory.decodeFile(path, opts);
      int width = opts.outWidth;
       int height = opts.outHeight;
       float scaleWidth = 0.f, scaleHeight = 0.f;
       if (width > w || height > h) {
          // 缩放
          scaleWidth = ((float) width) / w;
          scaleHeight = ((float) height) / h;
      }
     opts.inJustDecodeBounds = false;
       float scale = Math.max(scaleWidth, scaleHeight);
        opts.inSampleSize = (int)scale;
        WeakReference<Bitmap> weak = new WeakReference<Bitmap>(BitmapFactory.decodeFile(path, opts));
       return Bitmap.createScaledBitmap(weak.get(), w, h, true);
     }