public static Bitmap getBitmapFromPath(String imgPath, int reqWidth, int reqHeight) {
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeFile(imgPath, options);

        // Calculate inSampleSize
        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

        // Decode bitmap with inSampleSize set
        options.inJustDecodeBounds = false;
        //避免出现内存溢出的情况，进行相应的属性设置。
        options.inPreferredConfig = Bitmap.Config.RGB_565;
        options.inDither = true;

        return BitmapFactory.decodeFile(imgPath, options);
    }

    public static int calculateInSampleSize( //参2和3为ImageView期待的图片大小
                                             BitmapFactory.Options options, int reqWidth, int reqHeight) {
        // 图片的实际大小
        final int height = options.outHeight;
        final int width = options.outWidth;
        //默认值
        int inSampleSize = 1;
        //动态计算inSampleSize的值
        if (height > reqHeight || width > reqWidth) {
            final int halfHeight = height/2;
            final int halfWidth = width/2;
            while( (halfHeight/inSampleSize) >= reqHeight && (halfWidth/inSampleSize) >= reqWidth){
                inSampleSize *= 2;
            }
        }
        return inSampleSize;
    }