Self sorting wardrobe

How to solve a classification problem

This tutorial will show you how to build an image classifier, taking you through creating the typical building blocks of a convolution neural network (CNN) for a 28 x 28 pixels imageset with 10 classes.

12 - Target audience: Beginners

You will learn to
12 - Run multiple experiments.
12 - Understand the building blocks of a deep learning model.

Preread: We suggest that you start your deep dive into the Peltarion Platform with the Deploy an operational AI model tutorial. The link below is a proposed pre-read material for those unfamiliar with CNNs and how they work. It does not endeavor to be an exhaustive learning reference.
A Beginner’s Guide To Understanding Convolutional Neural Networks.


The problem

McKinsey Global Institute identifies the retail industry as the sector likely to create the most annual value from AI techniques (a potential $600B). They state in 2017 “AI technologies could eliminate many levels of manual activities in areas such as promotions, assortments, and supply chain. AI will enable retailers to increase both the number of customers and the average amount they spend by creating personal and convenient shopping experiences.”

Wardrobe

Deep learning image classification has many applications in the retail industry and will drive much of this predicted value, for example, reducing errors in supply chain management (accurate inventory/catalog management by automatically identifying items from photo) or as a component in visual search from user-generated content (a customer uses a photo taken on their mobile device to locate or search for similar items in a shopping catalog).

Using a convolutional neural network

Image classification in deep learning is often implemented using a technique called a convolutional neural network (CNN). In this tutorial, we will be building a CNN that will be trained on thousands of images of fashion items (e.g., clothing, accessories, shoes) that will create a model that can be used to predict for a given image what type of fashion item it is.

Although the CNN model, in this case, will identify fashion items, it can be trained on any class you require. For example, in healthcare, this technique could take a brain scan as input and predict if it contains a tumor or it could be used to classify a personal photo library, much as Apple or Google do with their photo applications.


Create project

First, create a project and name it, so you know what kind of project it is. Naming is important.

New project icon

A project combines all of the steps in solving a problem, from the preprocessing of datasets to model building, evaluation and deployment.


Add and manage the dataset

After creating the project, you will be taken to the Datasets view, where you can import data.

Click the Data library button and look for the Fashion MNIST - tutorial data dataset in the list.

The Fashion MNIST dataset is an image classification dataset that consists of small, 28 x 28 pixels, images of clothing or accessories such as shirts, bags, shoes, and other fashion items. Each image is annotated with a label indicating the correct garment. The images come from Zalando and consist of a training set of 60,000 examples and a test set of 10,000 examples.

If you agree with the license, click Accept and import. This will import the dataset in your project, and you will be taken to the dataset’s details where you can edit features and subsets.

Fashion MNIST dataset

Subsets of the Fashion MNIST dataset

Keep the default subsets.

The dataset is by default split into two subsets: 80% for training and 20% for validation. That means we’ll use 80% of the set to train our model and the remaining as "not seen before" examples to see how well the training is progressing. The percentage of correctly guessed labels on the validation set will produce the accuracy number we’re after.

Save the dataset

You’ve now created a dataset ready to be used in the platform. Click Save version. Saving this version will lock and version it and allow you to build a model with it. Click on Use in new experiment.


Select a CNN model

CNN model for fashion images
Figure 1. CNN model for fashion images

It’s time to create an experiment in the Modeling view. The experiment contains all the information needed to reproduce the experiment; the dataset, the AI model, the settings or parameters used to run the experiment.

  1. Make sure that the FashionMNIST dataset is selected in the Experiment wizard.

  2. Click on the Choose snippet tab and select the CNN snippet.

  3. Click Create.
    This will add a complete convolutional neural network (CNN) to the experiment.

CNN explained

A CNN is often used when you want to solve an image classification problem. This network looks for low-level features such as edges and curves and then builds up to more abstract concepts through a series of convolutional layers. The CNN snippet consists of the following types of blocks:

  • 2D Convolution. This block is used to detect spatial features in an image.

  • 2D Max pooling. This layer reduces the size of the data. You can say that 2D max pooling is similar to scaling down the size of an image.

  • Batch normalization. This normalizes all input features to a similar range of values which will speed up learning.

  • 2D Global average pooling. This block is used as an alternative to the Flatten block as it reduces the tensor of the last convolution layer from HxWx128 to a tensor of size 1x1x128.

  • Dense. This is a densely connected neural network layer.

Model settings

The experiment is done and ready to be trained. All settings have been pre-populated by the platform, e.g.,

  • The input feature is set to image in the Input block.

  • The target feature is set to category in the Target block. The Loss, is set to Categorical crossentropy. This loss function computes a score that the model uses to decide which garment it is depicted in the image. If there were only 2 classes in our data (t-shirts and shoes), you could choose binary crossentropy. We have 10 classes, thus categorical crossentropy.

  • In the last Dense block in the model the Nodes value is set to 10. This is the number of labels.
    The ​Activation is set to Softmax​​. This activation function is often used together with categorical crossentropy. The softmax function highlights the largest values and suppresses low values. This in effect allows only 1 of the 10 nodes of the dense layer to put its hand up. There are times when you don’t want to squash all in favor of one (like saying this t-shirt is both red and has a logo), but in this experiment we’re trying to say "this is a t-shirt and not a coat or a bag or trousers or…​”.


Run experiment to train model

Your model is now ready to be trained. Navigate to the Settings tab in the Inspector. In the Run settings section change Batch size to 256 and keep the default values for the rest. For your info:

  • Batch size is how many rows (examples) that are computed at the same time.

  • One Epoch is when the complete dataset has run through the model one time. That means that if you set Epochs to 10 the complete dataset has run through the model a 10 times.

  • Data access seed is just a random number.

  • The Optimizer is how the system optimizes the loss with respect to the weights of the network.

Done! Click Run.

Run button

More experiments

OK, let’s see if you can improve the model while the first model trains.

Note
If you’re on the Free plan you can run 1 experiment at a time. All other plans can run concurrent experiments.

The first thing to do would be to try some regularization, by adding Dropout blocks after the Dense block. Try a droput rate in the range 0.1-0.5.

Other ways to improve the model is to add blocks and change settings in the model. As long as you keep the same loss function, you can compare the results of the experiments and see which one is the best in the Evaluation view.

Examples of what you can change:

  • Add more dense blocks

  • Increase or decrease number of nodes in the dense layers

  • Change the width and height of the convolutional filters

  • Add another CNN snippet

  • Change batch size

  • etc.


Analyze experiments

Navigate to the Evaluation view and select your experiment in the left side Experiment section. Watch it train epoch by epoch.

Aim for high accuracy

In this tutorial, it’s validation accuracy that matters. Accuracy is how often you predict the right answer, or actually, the formula is:

\[Accuracy = \frac{Number\;of\;correct\;predictions}{Total\;number\;of\;examples}\]

For example, if the number of test samples is 1,000 and the model classifies 952 of those correctly, then the model’s accuracy is 95.2%.

We’ll set our goal to 0.9, i.e., correct prediction 9 out of 10 times. Note that the “world record” is 0.967. For more benchmarks, check Zalando’s collected benchmark classifiers here: Fashion MNIST benchmark.

Select the Accuracy graph and you’ll notice that your first experiment the training and validation graphs diverge after a few epochs, the experiment starts to overfit. That means that the model is just memorizing the picture vs. understanding in more general terms what the shapes and shadows may depict.

tut3 5
Figure 2. Accuracy graph

At the best epoch we have accuracy 0.91. Does that beat the goal you set? Yes, it does!

Confusion matrix

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Figure 3. Confusion matrix

The Confusion matrix is used to see how well a system does classification. In a perfect classification, you’ll have 100% on the diagonal going from top left to bottom right.


Tutorial recap

This tutorial has shown you how fast and easy you can create and test experiments on the Peltarion Platform. You’ve built a basic CNN model to solve a classification problem and acquired some basic deep learning knowledge.


Next steps / Read more

In this tutorial, only one label can be correct, but what if the object could have many labels, i.e., a shirt can be labeled both “red” and “short sleeve.” How do you solve such a problem? Check out our tutorial Predicting mood from raw audio data and learn how to solve a multi-label classification problem.

DJ set
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