title: What does the padding of tf.nn.conv2d_transpose do?
body: <p>As we know, we can calculate the shape of output <code>tensor</code> by padding mode for <code>conv2d</code>, and the <a href="https://www.tensorflow.org/api_guides/python/nn#Convolution" rel="nofollow noreferrer">algorithm</a> is clear, but I'm very confused about <code>conv2d_transpose</code>, does it pad the input tensor and then invoke <code>conv2d</code>? And where does it transpose filter or input?  How to calculate the shape of output tensor according to the padding mode, <code>SAME</code> or <code>VALID</code> for <code>conv2d_transpose</code>?</p>