Keras balanced batch generator

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Last Updated on October 3, On top of that, individual models can be very slow to train. In this post you will discover how you can use the grid search capability from the scikit-learn python machine learning library to tune the hyperparameters of Keras deep learning models. Discover how to develop deep learning models for a range of predictive modeling problems with just a few lines of code in my new bookwith 18 step-by-step tutorials and 9 projects.

In this post, I want to show you both how you can use the scikit-learn grid search capability and give you a suite of examples that you can copy-and-paste into your own project as a starting point.

Keras models can be used in scikit-learn by wrapping them with the KerasClassifier or KerasRegressor class. The constructor for the KerasClassifier class can take default arguments that are passed on to the calls to model.

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You can learn more about the scikit-learn wrapper in Keras API documentation. This is a map of the model parameter name and an array of values to try. By default, accuracy is the score that is optimized, but other scores can be specified in the score argument of the GridSearchCV constructor. By default, the grid search will only use one thread. The GridSearchCV process will then construct and evaluate one model for each combination of parameters.

Cross validation is used to evaluate each individual model and the default of 3-fold cross validation is used, although this can be overridden by specifying the cv argument to the GridSearchCV constructor. Once completed, you can access the outcome of the grid search in the result object returned from grid. All examples will be demonstrated on a small standard machine learning dataset called the Pima Indians onset of diabetes classification dataset.

This is a small dataset with all numerical attributes that is easy to work with. As we proceed through the examples in this post, we will aggregate the best parameters. This is not the best way to grid search because parameters can interact, but it is good for demonstration purposes.

In this first simple example, we look at tuning the batch size and number of epochs used when fitting the network. It is also an optimization in the training of the network, defining how many patterns to read at a time and keep in memory. The number of epochs is the number of times that the entire training dataset is shown to the network during training. In this example, we tune the optimization algorithm used to train the network, each with default parameters.

This is an odd example, because often you will choose one approach a priori and instead focus on tuning its parameters on your problem e.

[Keras] Transfer-Learning for Image classification with effificientNet

Here we will evaluate the suite of optimization algorithms supported by the Keras API. It is common to pre-select an optimization algorithm to train your network and tune its parameters. In this example, we will look at optimizing the SGD learning rate and momentum parameters. Learning rate controls how much to update the weight at the end of each batch and the momentum controls how much to let the previous update influence the current weight update.

We will try a suite of small standard learning rates and a momentum values from 0. Generally, it is a good idea to also include the number of epochs in an optimization like this as there is a dependency between the amount of learning per batch learning ratethe number of updates per epoch batch size and the number of epochs.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

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Cross Validated is a question and answer site for people interested in statistics, machine learning, data analysis, data mining, and data visualization.

It only takes a minute to sign up. I have noticed that we can provide class weights in model training through Keras APIs. However, I could not locate a clear documentation on how this weighting works in practice. Now, to balance this how should I assign class weights? Greater weight leads to greater importance, so single case with greater weight may be worth more then multiple cases with smaller weights. Sign up to join this community. The best answers are voted up and rise to the top.

Home Questions Tags Users Unanswered. Handling imbalanced data in Keras Ask Question.

keras balanced batch generator

Asked 2 years, 1 month ago. Active 2 years, 1 month ago. Viewed 6k times. Active Oldest Votes. 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. Q2 Community Roadmap. The Overflow How many jobs can be done at home? Featured on Meta. Community and Moderator guidelines for escalating issues via new response…. Feedback on Q2 Community Roadmap. Related 9.

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Hot Network Questions. Question feed. Cross Validated works best with JavaScript enabled.Keras and TensorFlow 2. In the first half of this tutorial, you will learn how to implement sequential, functional, and model subclassing architectures using Keras and TensorFlow 2. Our models. The training script, train. A sequential model, as the name suggests, allows you to create models layer-by-layer in a step-by-step fashion.

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Examples of seminal sequential architectures that you may have already used or implemented include:. Open up the models. Notice on each of these lines of code that we call model. Order matters — you must call model.

To gain experience using TensorFlow 2. Think of each of these modules as Legos — we implement each type of Lego and then stack them in a particular manner to define our model architecture. Legos can be organized and fit together in a near-infinite number of possibilities; however, since form defines function, we need to take care and consider how these Legos should fit together. Defining the modules as sub-functions like this allows us to reuse the structure and save on lines of code, not to mention making it easier to read and make modifications.

Thus, they can be concatenated along the channel dimension. Additionally, I want to give credit to Zhang et al. The third and final method to implement a model architecture using Keras and TensorFlow 2. Inside of Keras the Model class is the root class used to define a model architecture. Since Keras utilizes object-oriented programming, we can actually subclass the Model class and then insert our architecture definition.

Model subclassing is fully-customizable and enables you to implement your own custom forward-pass of the model.

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From there, our layers are defined as instance attributes, each with its own name Lines The answer lies inside train. The heart of the script lies in this next code block where we instantiate our model:. Here we check if either our Sequential, Functional, or Model Subclassing architecture should be instantiated. You may read about the. Lines make predictions on the test set and evaluate the network.

A classification report is printed to the terminal. From there, open up a terminal and execute the following command to train and evaluate a Sequential model:. We used Keras model subclassing here rather than the Sequential API as a simple example of how you may take an existing model and convert it to subclassed architecture.

Note: Implementing your own custom layer types and training procedures for the model subclassing API is outside the scope of this post but I will cover it in a future guide. My complete, self-study deep learning book is trusted by members of top machine learning schools, companies, and organizations, including Microsoft, Google, Stanford, MIT, CMU, and more! Readers of my book have gone on to win Kaggle competitionssecure academic grantsand start careers in CV and DL using the knowledge they gained through study and practice.

My book not only teaches the fundamentals, but also teaches advanced techniques, best practices, and tools to ensure that you are armed with practical knowledge and proven coding recipes to tackle nearly any computer vision and deep learning problem presented to you in school, research, or the modern workforce.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Data Science Stack Exchange is a question and answer site for Data science professionals, Machine Learning specialists, and those interested in learning more about the field. It only takes a minute to sign up. Would somebody so kind to provide one? By the way, in this case the appropriate praxis is simply to weight up the minority class proportionally to its underrepresentation? If you are talking about the regular case, where your network produces only one output, then your assumption is correct.

In order to force your algorithm to treat every instance of class 1 as 50 instances of class 0 you have to:. EDIT: "treat every instance of class 1 as 50 instances of class 0 " means that in your loss function you assign higher value to these instances.

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Adjust accordingly when copying code from the comments. That means that you should pass a 1D array with the same number of elements as your training samples indicating the weight for each of those samples.

This means you should pass a weight for each class that you are trying to classify. If you need more than class weighting where you want different costs for false positives and false negatives. With the new keras version now you can just override the respective loss function as given below. Note that weights is a square matrix. I found the following example of coding up class weights in the loss function using the minist dataset.

This works with a generator or standard. Your largest class will have a weight of 1 while the others will have values greater than 1 depending on how infrequent they are relative to the largest class. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. How to set class weights for imbalanced classes in Keras?

Ask Question. Asked 3 years, 7 months ago. Active yesterday. Viewed k times. Hendrik Hendrik 5, 13 13 gold badges 32 32 silver badges 49 49 bronze badges. Active Oldest Votes.

Is it that the in training set, row corresponding to class 1 is duplicated 50 times in order to make it balanced or some other process follows? Toby 3 3 bronze badges. PSc PSc 1, 1 1 gold badge 4 4 silver badges 5 5 bronze badges. Lee Oct 13 '17 at Even then, the total of each of my labels is not balanced. How would I use class weights with that?

Guillaumin J. Guillaumin 2 2 silver badges 2 2 bronze badges.In this post I would like to show how to use a pre-trained state-of-the-art model for image classification for your custom data. For this we utilize transfer learning and the recent efficientnet model from Google. An example for the standford car dataset can be found here in my github repository. Starting from an initially simple convolutional neural network CNNthe precision and efficiency of a model can usually be further increased step by step by arbitrarily scaling the network dimensions such as width, depth and resolution.

Increasing the number of layers used or using higher resolution images to train the models usually involves a lot of manual effort. Researchers from the Google AI released EfficientNet few months ago, a scaling approach based on a fixed set of scaling coefficients and advances in AutoML and other techniques e. Rather than independently optimizing individual network dimensions as was previously the case, EfficientNet is now looking for a balanced scaling process across all network dimensions.

With EfficientNet the number of parameters is reduces by magnitudes, while achieving state-of-the-art results on ImageNet.

While EfficientNet reduces the number of parameters, training of convolutional networks is still a time-consuming task. To further reduce the training time, we are able to utilize transfer learning techniques. Transfer learning means we use a pretrained model and fine tune the model on new data. In image classification we can think of dividing the model into two parts.

One part of the model is responsible for extracting the key features from images, like edges etc. Usually a CNN is built of stacked convolutional blocks reducing the image size while increasing the number of learnable features filters and in the end everything is put together into a fully connected layer, which does the classification.

Now we can train the last layer on our custom data, while the feature extraction layers are using the weights from imageNet. But unfortunately we might see this results:. This weird behavior comes from the BatchNormalization layer. It seems like there is a bugwhen keras 2. However we could ignore this, because besides the weird validation accuracy scores, our layer still learns, as we can see in the training accuracy Read more about different normalization layers here.

But to fix it, we can make the BatchNormalization layer trainable:. On the other hand we got reasonable results for validation:. We still have additional benefits, when training the last layer s only. For example, we have less trainable parameters, which means faster computation time. Therefore we make all the layers trainable and fit the model again. To get an estimate of the memory required by the model look here stackoverflow.

keras balanced batch generator

I also suggest making use of early stopping. Your Message. Name required. Mail required. EfficientNet Starting from an initially simple convolutional neural network CNNthe precision and efficiency of a model can usually be further increased step by step by arbitrarily scaling the network dimensions such as width, depth and resolution. Transfer Learning While EfficientNet reduces the number of parameters, training of convolutional networks is still a time-consuming task.

But unfortunately we might see this results: Training and testing loss, when freezing all layers from the pretrained model Training and testing accuracy, when freezing all layers from the pretrained model The BatchNormalization weirdness This weird behavior comes from the BatchNormalization layer.

On the other hand we got reasonable results for validation: Training and testing loss, when unfreezing the BN layers from the pretrained mode Training and testing accuracy, when unfreezing the BN layers from the pretrained mode We still have additional benefits, when training the last layer s only.

After running fit the second time, we just applied transfer learning.

keras balanced batch generator

October 2, Previous post. Next post.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. The tutorial here demonstrates how a small but balanced dataset can be augmented using the ImageDataGenerator.

Is there an easy way to use this generator to augment a heavily unbalanced dataset, such that the resulting, generated dataset is balanced? This would not be a standard approach to deal with unbalanced data. Nor do I think it would be really justified - you would be significantly changing the distributions of your classes, where the smaller class is now much less variable. The larger class would have rich variation, the smaller would be many similar images with small affine transforms.

They would live on a much smaller region in image space than the majority class. The first two options are really kind of hacks, which may harm your ability to cope with real world imbalanced data. Neither really solves the problem of low variability, which is inherent in having too little data.

If application to a real world dataset after model training isn't a concern and you just want good results on the data you have, then these options are fine and much easier than making generators for a single class.

If you truly want to generate a variety of augmented images for one class over another, it would probably be easiest to do it in pre-processing. Take the images of the minority class and generate some augmented versions, and just call it all part of your data.

Like I say, this is all pretty hacky. Learn more. Asked 3 years, 2 months ago. Active 1 month ago. Viewed 10k times. The keras ImageDataGenerator can be used to " Generate batches of tensor image data with real-time data augmentation " The tutorial here demonstrates how a small but balanced dataset can be augmented using the ImageDataGenerator.

Anshuman Kumar 1 1 gold badge 3 3 silver badges 15 15 bronze badges. Active Oldest Votes. Deep learning can cope with this, it just needs lots more data the solution to everything, really. Utkarsh Sinha 3, 4 4 gold badges 25 25 silver badges 42 42 bronze badges. Thanks a lot for sharing your insight. I will look into that google paper. 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. The Overflow How many jobs can be done at home? Featured on Meta. Community and Moderator guidelines for escalating issues via new response…. Feedback on Q2 Community Roadmap. Triage needs to be fixed urgently, and users need to be notified upon….Have you ever had to load a dataset that was so memory consuming that you wished a magic trick could seamlessly take care of that? Large datasets are increasingly becoming part of our lives, as we are able to harness an ever-growing quantity of data.

We have to keep in mind that in some cases, even the most state-of-the-art configuration won't have enough memory space to process the data the way we used to do it. That is the reason why we need to find other ways to do that task efficiently. In this blog post, we are going to show you how to generate your dataset on multiple cores in real time and feed it right away to your deep learning model.

The framework used in this tutorial is the one provided by Python's high-level package Keraswhich can be used on top of a GPU installation of either TensorFlow or Theano. This article is all about changing the line loading the entire dataset at once. Indeed, this task may cause issues as all of the training samples may not be able to fit in memory at the same time. In order to do so, let's dive into a step by step recipe that builds a data generator suited for this situation.

Before getting started, let's go through a few organizational tips that are particularly useful when dealing with large datasets. Let ID be the Python string that identifies a given sample of the dataset. A good way to keep track of samples and their labels is to adopt the following framework:. Create a dictionary called labels where for each ID of the dataset, the associated label is given by labels[ID]. For example, let's say that our training set contains id-1id-2 and id-3 with respective labels 01 and 2with a validation set containing id-4 with label 1.

In that case, the Python variables partition and labels look like. Also, for the sake of modularitywe will write Keras code and customized classes in separate files, so that your folder looks like. Finally, it is good to note that the code in this tutorial is aimed at being general and minimalso that you can easily adapt it for your own dataset.

Now, let's go through the details of how to set the Python class DataGeneratorwhich will be used for real-time data feeding to your Keras model. First, let's write the initialization function of the class. We make the latter inherit the properties of keras. Sequence so that we can leverage nice functionalities such as multiprocessing. We put as arguments relevant information about the data, such as dimension sizes e.

keras balanced batch generator

We also store important information such as labels and the list of IDs that we wish to generate at each pass. If the shuffle parameter is set to Truewe will get a new order of exploration at each pass or just keep a linear exploration scheme otherwise. Shuffling the order in which examples are fed to the classifier is helpful so that batches between epochs do not look alike. Doing so will eventually make our model more robust. Another method that is core to the generation process is the one that achieves the most crucial job: producing batches of data.

During data generation, this code reads the NumPy array of each example from its corresponding file ID. Since our code is multicore-friendly, note that you can do more complex operations instead e.

Also, please note that we used Keras' keras. Now comes the part where we build up all these components together. Now, we have to modify our Keras script accordingly so that it accepts the generator that we just created. Keras takes care of the rest! A high enough number of workers assures that CPU computations are efficiently managed, i.


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