//加载原图

        Bitmap bmSrc = BitmapFactory.decodeResource(getResources(), R.drawable.photo3);

        //创建副本

        //1.创建与原图一模一样大小的bitmap对象，该对象中目前是没有内容的，可以比喻为创建了和原图一样大小

        //的白纸

        Bitmap bmCopy = Bitmap.createBitmap(bmSrc.getWidth(), bmSrc.getHeight(), bmSrc.getConfig());

        //2.创建画笔对象

        Paint paint = new Paint();

        //3.创建画板，把白纸铺到画板上

        Canvas canvas = new Canvas(bmCopy);

        //4.开始作画

        canvas.drawBitmap(bmSrc, new Matrix(), paint);

        ImageView iv1 = (ImageView) findViewById(R.id.iv1);

        ImageView iv2 = (ImageView) findViewById(R.id.iv2);

        iv1.setImageBitmap(bmSrc);

        iv2.setImageBitmap(bmCopy);

Options opts = new Options();

        //只请求图片宽高，不解析图片像素(请求图片属性但不申请内存，解析bitmap对象，该对象不占内存)

        opts.inJustDecodeBounds = true;

        //String path = Environment.getExternalStorageDirectory() + "/dog.jpg";

        BitmapFactory.decodeFile("sdcard/dog.jpg", opts);

        int imageWidth = opts.outWidth;

        int imageHeight = opts.outHeight;

        //获取屏幕的宽和高

        Display dp = getWindowManager().getDefaultDisplay();

        int screenWidth = dp.getWidth();

        int screenHeight = dp.getHeight();

        //图片的宽高除以屏幕的宽高，算出宽和高的缩放比例，取较大值作为图片的缩放比例

        int scale = 1;

        int scaleX = imageWidth / screenWidth;

        int scaleY = imageHeight / screenHeight;

        if(scaleX >= scaleY && scaleX > 1){

            scale = scaleX;

        }else if(scaleX < scaleY && scaleY > 1){

            scale = scaleY;

        }

        System.out.println(scale);

        //按照缩放比例加载图片

        //设置缩放比例

        opts.inSampleSize = scale;

        //为图片申请内存

        opts.inJustDecodeBounds = false;

        Bitmap bm = BitmapFactory.decodeFile("sdcard/dog.jpg", opts);

        iv.setImageBitmap(bm);