JPEG-resistant Adversarial Images

摘要：

While JPEG compression is not differentiable, we show how to closely approximate it using only differentiable operations

• differentiable approximation to rounding:

  
  
  
  
  

  原本的方式使得导数几乎处处为0，与FGSM方法不兼容，因此改成用以上式子的方法

• Creating JPEG-resistant adversarial images

In this paper, we showed how to defeat the JPEG defense by performing an adaptive attack with a differentiable JPEG approximation. By ensembling target models that use varying amounts of compression, our adversarial examples generalize to models with and without this defense.

在input阶段，对图像进行jpeg compression时使用(a differentiable JPEG approximation)，也就是说，我们优化问题变为:
这需要计算梯度:

此时compress对fgsm的防御能力会下降。