Colour image classification (CIFAR-10) using a CNN

As I mentioned in a previous post, a convolutional neural network (CNN) can be used to classify colour images in much the same way as grey scale classification. The way to achieve this is by utilizing the depth dimension of our input tensors and kernels. In this example I'll be using the CIFAR-10 dataset, which consists of 32x32 colour images belonging to 10 different classes. You can see a few examples of each class in the following image from the CIFAR-10 website: Although previously I've talked about the Lasagne and nolearn packages (here and here), extending those to colour images…

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April 4, 2018

Machine Learning

Visualizing Convolutional Neural Networks using nolearn

We previously talked about Convolutional Neural Networks (CNN) and how use them to recognize handwritten digits using Lasagne. While we can manually extract kernel parameters to visualize weights and activation maps (as discussed in the previous post), the nolearn package offers an easy way to visualize different elements of CNNs. nolearn is a wrapper around Lasagne (which itself is a wrapper around Theano), and offers some nice visualization options such as plotting occlusion maps to help diagnose the performance of a CNN model. Additionally, nolearn offers a very high level API that makes model training even simpler than with Lasagne. In…

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March 18, 2018

Machine Learning

Handwritten digit recognition with a CNN using Lasagne

Following my overview of Convolutional Neural Networks (CNN) in a previous post, now lets build a CNN model to 1) classify images of handwritten digits, and 2) see what is learned by this type of model. Handwritten digit recognition is the 'Hello World' example of the CNN world. I'll be using the MNIST database of handwritten digits, which you can find here. The MNIST database contains grey scale images of size 28x28 (pixels), each containing a handwritten number from 0-9 (inclusive). The goal: given a single image, how do we build a model that can accurately recognize the number that…

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March 2, 2018

Machine Learning

XOR Logic Gate – Neural Networks

We have previously discussed OR logic gates and the importance of bias units in AND gates. Here, we will introduce the XOR gate and show why logistic regression can't model the non-linearity required for this particular problem. As always, the full code for these examples can be found in my GitHub repository here. XOR gates output True if either of the inputs are True, but not both. It acts like a more specific version of the OR gate: Input 1Input 2Output000011101110 If we visualize the data space we'll have a clearer sense of what causes the issue. As you can…

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February 13, 2017

Machine Learning

AND Logic Gate – Importance of bias units

Previously, we talked about simple OR gates and now we'll continue that discussion with AND gates, and specifically the role of bias units. We often neglect to consider the role bias plays in our models. We know that we should include bias units, but why? Here, I'll walk through a short example using an AND gate to highlight the importance of the bias unit. Bias units allow us to offset the model in the same way that an intercept allows us to offset a regression line. Imagine a simple AND gate. It will only fire if both inputs are true:…

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December 29, 2016

Machine Learning

OR Logic Gate using Theano

Theano is a powerful Python library that provides some useful tools for machine learning, such as GPU training and symbolic differentiation of the cost function during gradient descent. It can be a bit challenging to understand how Theano works, so before jumping into more complex non-linear models, we can get to grips with Theano by implementing something simple like an OR gate. An OR gate receives 2 inputs and will output true if either of the inputs are true. So, there are 3 cases where an OR gate will output a true value: Input 1Input 2Output000011101111 We can also represent…

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December 24, 2016