twifold

1. Twifold infection

雙重感染

2. to recognize the twifold features of teaching habits;

認識教學習慣的雙重特征；

3. Firstly, to ensure the security of wartermark,the wartermark image is Arnold scrambled before embedding and expanded to the twifold size of the original image.

首先，為保證水印的安全性，在嵌入之前先對水印圖像作Arnold置亂處理，再將水印圖像位擴展為原始圖像的兩倍大小；