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 weak = new WeakReference(BitmapFactory.decodeFile(path, opts)); 
       return Bitmap.createScaledBitmap(weak.get(), w, h, true); 
     }