<h2>Unpooling</h2>

<p>As etoropov wrote, you can read about unpooling in <a href="http://arxiv.org/pdf/1311.2901v3.pdf" rel="noreferrer">Visualizing and Understanding Convolutional Networks</a> by Zeiler and Ferguson:</p>

<blockquote>
  <p>Unpooling: In the convnet, the max pooling operation
  is non-invertible, however we can obtain an approximate
  inverse by recording the locations of the
  maxima within each pooling region in a set of switch
  variables. In the deconvnet, the unpooling operation
  uses these switches to place the reconstructions from
  the layer above into appropriate locations, preserving
  the structure of the stimulus. See Fig. 1(bottom) for
  an illustration of the procedure.</p>
</blockquote>

<h2>Deconvolution</h2>

<p>Deconvolution works like this:</p>

<ul>
<li>You add padding around each pixel</li>
<li>You apply a convolution</li>
</ul>

<p>For example, in the following illustration the original blue image is padded with zeros (white), the gray convolution filter is applied to get the green output.</p>

<p><img src="https://i.stack.imgur.com/f2RiP.gif" alt=""></p>

<p>Source: <a href="https://datascience.stackexchange.com/q/6107/8820">What are deconvolutional layers?</a></p>
How does the unpooling and deconvolution work in DeConvNet
<p>I have been trying to understand how unpooling and deconvolution works in DeConvNets. </p>

<p>Unpooling</p>

<p>While during the unpooling stage, the activations are restored back to the locations of maximum activation selections, which makes sense, but what about the remaining activations? Do those remaining activations need to be restored as well or interpolated in some way or just filled as zeros in unpooled map.</p>

<p>Deconvolution</p>

<p>After the convolution section (i.e., Convolution layer, Relu, Pooling ), it is common to have more than one feature map output, which would be treated as input channels to successive layers ( Deconv.. ). How could these feature maps be combined together in order to achieve the activation map with same resolution as original input?</p>