bitmap內存溢出的問題

我的代碼如下

    is = new FileInputStream(new File(baseMagazinePath + this.bookId + "/" + fileList[currentImgNo] + ".png"));
    iv.setImageDrawable(Drawable.createFromStream(is, "myStream"));

有時候出現內存溢出

改爲 
    is = new FileInputStream(new File(baseMagazinePath + this.bookId + "/" + fileList[currentImgNo] + ".png"));
    BitmapFactory.Options opts = new BitmapFactory.Options(); 
    opts.inSampleSize = 4;
    Bitmap bitmap = BitmapFactory.decodeStream(is, null, opts); 
    iv.setImageBitmap(bitmap);

就好了。