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- Implementing Autoencoders in Keras: Tutorial
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## keras-tutorials

Welcome to Part 4 of Applied Deep Learning series. Part 1 was a hands-on introduction to Artificial Neural Networks, covering both the theory and application with a lot of code examples and visualization. In Part 2 we applied deep learning to real-world datasets, covering the 3 most commonly encountered problems as case studies: binary classification, multiclass classification and regression. Part 3 explored a specific deep learning architecture: Autoencoders. Now we will cover the most popular deep learning model: Convolutional Neural Networks. The code for this article is available here as a Jupyter notebook, feel free to download and try it out yourself. It is arguably the most popular deep learning architecture. The recent surge of interest in deep learning is due to the immense popularity and effectiveness of convnets. In just three years, researchers progressed from 8 layer AlexNet to layer ResNet. CNN is now the go-to model on every image related problem. In terms of accuracy they blow competition out of the water. It is also successfully applied to recommender systems, natural language processing and more. The main advantage of CNN compared to its predecessors is that it automatically detects the important features without any human supervision. For example, given many pictures of cats and dogs it learns distinctive features for each class by itself. CNN is also computationally efficient. It uses special convolution and pooling operations and performs parameter sharing. This enables CNN models to run on any device, making them universally attractive. All in all this sounds like pure magic. We are dealing with a very powerful and efficient model which performs automatic feature extraction to achieve superhuman accuracy yes CNN models now do image classification better than humans. Hopefully this article will help us uncover the secrets of this remarkable technique. All CNN models follow a similar architecture, as shown in the figure below. If we are performing multiclass classification the output is softmax. We will now dive into each component. The main building block of CNN is the convolutional layer. Convolution is a mathematical operation to merge two sets of information. In our case the convolution is applied on the input data using a convolution filter to produce a feature map. On the left side is the input to the convolution layer, for example the input image. On the right is the convolution filteralso called the kernelwe will use these terms interchangeably. This is called a 3x3 convolution due to the shape of the filter. We perform the convolution operation by sliding this filter over the input. At every location, we do element-wise matrix multiplication and sum the result. This sum goes into the feature map. The green area where the convolution operation takes place is called the receptive field. Due to the size of the filter the receptive field is also 3x3. We then slide the filter to the right and perform the same operation, adding that result to the feature map as well. We continue like this and aggregate the convolution results in the feature map.## Subscribe to RSS

By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I have done a few readings and play codes with keras including this one. First of all, the aim of an autoencoder is to learn a representation encoding for a set of data, typically for the purpose of dimensionality reduction. So, the target output of the autoencoder is the autoencoder input itself. It is shown in [1] that If there is one linear hidden layer and the mean squared error criterion is used to train the network, then the k hidden units learn to project the input in the span of the first k principal components of the data. And in [2] you can see that If the hidden layer is nonlinear, the autoencoder behaves differently from PCA, with the ability to capture multi-modal aspects of the input distribution. Autoencoders are data-specific, which means that they will only be able to compress data similar to what they have been trained on. So, the usefulness of features that have been learned by hidden layers could be used for evaluating the efficacy of the method. Generally, PCA is a linear method, while autoencoders are usually non-linear. Mathematically, it is hard to compare them together, but intuitively I provide an example of dimensionality reduction on MNIST dataset using Autoencoder for your better understanding. The code is here:. For example, here you see the outputs of layer y for a digit 5 instance in dataset:. As you see in the above code, when we connect layer y to a softmax dense layer:. So, it would be reasonable to say that yis an efficiently extracted feature vector for the dataset. The earlier answer cover the whole thing, however I am doing the analysis on the Iris data - my code comes with a slightly modificiation from this post which dives further into the topic. As it was request, lets load the data. A very simple AE model with linear layers, as the earlier answer pointed out with Where the idea of variance explanation is not there, still one can look into the convergence. Learn more. Asked 2 years, 7 months ago. Active 4 months ago. Viewed 4k times. I am playing with a toy example to understand PCA vs keras autoencoder I have the following code for understanding PCA: import numpy as np import matplotlib. However, the reference code feels too high a leap for my level of understanding. Does someone have a short auto-encoder code which can show me 1 how to pull the first 3 components from auto-encoder 2 how to understand what amount of variance the auto-encoder captures 3 how the auto-encoder components compare against PCA components. Zanam Zanam 3, 7 7 gold badges 32 32 silver badges 67 67 bronze badges. Active Oldest Votes. The code is here: from keras. As it was request, lets load the data from sklearn. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog.

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GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. If nothing happens, download GitHub Desktop and try again. If nothing happens, download Xcode and try again. If nothing happens, download the GitHub extension for Visual Studio and try again. To run the code, you are required to install Tensorflow and Tensorlayer on your machine. Check this how to load and use a pretrained VGG? Firstly, download the celebA dataset and VGG weights. After installing all the third-party packages required, we can train the models by:. Skip to content. Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Sign up. Variational auto-encoder trained on celebA. All rights reserved. Python Branch: master. Find file. Sign in Sign up. Go back. Launching Xcode If nothing happens, download Xcode and try again. Latest commit. Latest commit d Dec 14, Result: plain VAE. You signed in with another tab or window. Reload to refresh your session. You signed out in another tab or window. Typo Fixed in Readme. Dec 14, Add files via upload. Aug 14, Sep 15,

## Implementing Autoencoders in Keras: Tutorial

Autoencoders AE are a family of neural networks for which the input is the same as the output they implement a identity function. They work by compressing the input into a latent-space representation, and then reconstructing the output from this representation. A really popular use for autoencoders is to apply them to images. The trick is to replace fully connected layers by convolutional layers. This helps the network extract visual features from the images, and therefore obtain a much more accurate latent space representation. The reconstruction process uses upsampling and convolutions. Convolutional autoencoders can be useful for reconstruction. They can, for example, learn to remove noise from pictureor reconstruct missing parts. With this process, the networks learns to fill in the gaps in the image. We can manually create the dataset, which is extremely convenient. Now that our autoencoder is trained, we can use it to remove the crosshairs on pictures of eyes we have never seen! The encoder part of the network will be a typical convolutional pyramid. Each convolutional layer will be followed by a max-pooling layer to reduce the dimensions of the layers. The decoder needs to convert from a narrow representation to a wide reconstructed image. They work almost exactly the same as convolutional layers, but in reverse. A stride in the input layer results in a larger stride in the transposed convolution layer. For example, if you have a 3x3 kernel, a 3x3 patch in the input layer will be reduced to one unit in a convolutional layer. Comparatively, one unit in the input layer will be expanded to a 3x3 path in a transposed convolution layer. However, transposed convolution layers can lead to artifacts in the final images, such as checkerboard patterns. This is due to overlap in the kernels which can be avoided by setting the stride and kernel size equal. In this Distill article from Augustus Odena, et althe authors show that these checkerboard artifacts can be avoided by resizing the layers using nearest neighbor or bilinear interpolation upsampling followed by a convolutional layer. In TensorFlow, this is easily done with tf.

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