title: Visualization of filters in convolution neural networks
body: <p>I read this article "<a href="http://ufldl.stanford.edu/wiki/index.php/Visualizing_a_Trained_Autoencoder" rel="nofollow noreferrer">ufldf</a>", it evolves visualization of hidden layers in autoencoder, but I'm confused how to visualize filters for a convolution neural networks.  In my opinion, for the first convolution layer, to visualize filters, it need this equation:</p>
  
  <p><img src="https://latex.codecogs.com/gif.latex?%5Cfrac%7Bfilter%7D%7B%5Csqrt%7B%5Csum%20filter%5E2(:))%7D%7D" alt="enter image description here"></p>
  
  <p>And for second convolution layer, it should project filters into original input space, but I don't know how to do it.</p>