“If you’ve read the previous two parts you’ll feel right at home implementing this one.”

← Part 2: Exploring latent space with Adversarial Autoencoders.

Parts 1 and 2 were mainly concerned with getting started on Autoencoders and Adversarial Autoencoders. We began with a simple AE (vanilla one) made some changes to its architecture and training algorithm to end up with an AAE. This part continues that trend by changing AAE’s architecture along with a small change in the way it’s trained.

I have created all the python files in my repo such that each one required for a part can be obtained from the previous one with some minor modifications. I would recommend you to read the theoretical aspects from this post and try to modify the code from part 2 to implement part 3.

Each and every one of us have our own unique style of writing, be it writing a letter or even a signature. The way in which we write certain characters, words we use often to create sentences, even the amount of pressure one exerts on paper are all characteristics which define a unique handwriting. With all these things coming into play, forging a handwriting can become very difficult and expensive. Let’s try to learn the style of writing from the MNIST dataset and use that to output images which all have the same style. We’ll only focus on the style of writing and not on the way sentences are framed or the thought process a writer goes through.

To get a clear picture of what style and content is, look at the image below:

Style and Content

Each of the texts has the same content “ Autoencoder”, but are in different styles. We now have the task of separating the style (Myriad Pro, MV Boil,…) and content from the images.

Disentanglement of various features is very important in representation learning (More on it here).

The Autoencoder and Adversarial Autoencoder we have come across are all trained in an unsupervised manner (there weren’t any labels used during training). Using the label info from an image allows an AAE to focus on learning to extract the style in an image without considering its content. Making use of image labels makes it a supervised model.

The architecture we’ll need to accomplish this is very similar to what we’ve seen in Part 2.

Here, instead of directly using the latent code z (output of the encoder) to recover the input image (x) at the decoder, we pass in the image labels (y) as well. Now, the input to the decoder has two parts:

• The latent codezfrom the encoder.
• One hot representation of the image label (let’s call it y).

We train the AAE as usual with a little modification made to the reconstruction phase:

• Reconstruction Phase: We pass in the input image to the encoder to get a latent code z and later, combine the latent code (z, output of the encoder) and the image label (y) to get a bigger column vector, which is then fed to our decoder. We train the AE to minimize the reconstruction loss as usual. Since the image label is being fed to the decoder, the encoder learns the style of an image during training and the decoder uses the content info from the label and the style info from the encoder to reconstruct the input image.
• Regularization Phase: Exactly similar to what we’ve seen in Part 2.

Now, let’s just add the image label to our AAE and check out the results.

Since we need one hot image labels the decoder architecture will have a larger number of input neurons [10 + z_dim] (10 cause we have ten classes and z_dim is the size of the encoder output, for example, z_dim can be 2).

Modified Decoder architecture:

We’ll also need to feed in the image labels during training which is super easy:

I’ve just replaced _ with batch_y when calling the mnist_train_next_batch() function and used these labels as inputs to the y_input placeholder.

I’ve trained the AE with the following parameters:

Note that I have used z_dim=15 instead of 2 unlike the previous implementations as the result were visually pleasing.

Similar to Part 2, I’ve maintained the standard deviation of the prior Gaussian distribution to be 5.0 and a mean of 0.

To generate images having the same style but with a different character we’ll pass in a random input as z(z_dimis 15 in this case) and change the one hot vector yto the desired value. Here I’ve passed in 10 random values for zand changed yto represent numbers from 0 to 9:

Have a look at generate_image_grid() for it’s implementation.

As a sanity check let’s have a look at the encoder output distribution to check if it’s still what we want it to be:

Yup, that completes part 3!

We’ll again build on what we have in this part to classify images using a limited number of labeled ones while still disentangling style and content.