mixup generator

This is an implementation of the mixup algorithm.

Mixup

Mixup [1] is a kind of image augmentation methods, which augments training data by mixing-up both of training images and labels by linear interpolation with weight lambda:

X = lambda * X1 + (1 - lambda) * X2,
y = lambda * y1 + (1 - lambda) * y2,

where lambda is drawn from the Beta distribution Be(alpha, alpha), and alpha is a hyperparameter.

Please check mixup_generator.py for implementation details.

Usage

Get MixupGenerator:

from mixup_generator import MixupGenerator
training_generator = MixupGenerator(x_train, y_train, batch_size=batch_size, alpha=0.2)()

• x_train : training images (#images x h x w x c)
• y_train : labels as one hot vectors (#images x #classes or list of #images x #classes for multi-task training)
• batch_size : batch size
• alpha : hyper parameter; lambda is drawn from the beta distribution Be(alpha, alpha).

Get mixed training batch:

x, y = next(generator)

Please refer to test_mixup.ipynb to see how it works.

Use MixupGenerator with fit_generator in Keras

It is very easy to use MixupGenerator in training if you are using Keras; Get MixupGenerator, and then fit model by fit_generator:

model.fit_generator(generator=training_generator,
                    steps_per_epoch=x_train.shape[0] // batch_size,
                    validation_data=(x_test, y_test),
                    epochs=epochs, verbose=1,
                    callbacks=callbacks)

Please refer to cifar10_resnet.py for complete example, which is imported from official Keras examples.

MixupGenerator with ImageDataGenerator

The MixupGenerator can be combined with keras.preprocessing.image.ImageDataGenerator for further image augmentation:

datagen = ImageDataGenerator(
    width_shift_range=0.1,
    height_shift_range=0.1,
    horizontal_flip=True)
    
training_generator = MixupGenerator(x_train, y_train, batch_size=batch_size, alpha=0.2, datagen=datagen)()

In this case, the mixed-up training images are further augmented by ImageDataGenerator.

Mixup with Random Erasing

Random Erasing [2] is a kind of image augmentation methods for convolutional neural networks (CNN). It tries to regularize models using training images that are randomly masked with random values.

Please refer to this repository for the details of algorithm and its implementation.

Mixup can be combined with Random Erasing via ImageDataGenerator by:

from random_eraser import get_random_eraser

datagen = ImageDataGenerator(
    width_shift_range=0.1,
    height_shift_range=0.1,
    horizontal_flip=True,
    preprocessing_function=get_random_eraser(v_l=0, v_h=255))

generator = MixupGenerator(x_train, y_train, alpha=1.0, datagen=datagen)()

The augmented images become like this:

Results

(!Only a single trial)

Without mixup:

Test loss: 0.862150103855
Test accuracy: 0.8978

With mixup alpha = 0.2:

Test loss: 0.510702615929
Test accuracy: 0.9117

With mixup alpha = 0.5:

Test loss: 0.48489781661
Test accuracy: 0.9181

With mixup alpha = 1.0:

Test loss: 0.493033925915
Test accuracy: 0.9167

References

[1] H. Zhang, M. Cisse, Y. N. Dauphin, and D. Lopez-Paz, "mixup: Beyond Empirical Risk Minimization," in arXiv:1710.09412, 2017.

[2] Z. Zhong, L. Zheng, G. Kang, S. Li, and Y. Yang, "Random Erasing Data Augmentation," in arXiv:1708.04896, 2017.