Generative Adversarial Models (GANs) are a class of generative models that consist of two neural networks: a generator and a discriminator. GANs are designed to generate new samples that resemble a given training dataset by learning the underlying data distribution.
The generator network takes random noise as input and generates synthetic samples. It aims to map the random noise to the data space such that the generated samples look similar to the real samples from the training set. Initially, the generator produces random and nonsensical outputs, but as it is trained, it learns to generate more realistic samples.
The discriminator network, on the other hand, acts as a binary classifier. It takes input samples and distinguishes between real samples from the training set and fake samples generated by the generator. The discriminator is trained to assign high probabilities to real samples and low probabilities to fake samples. The objective of the discriminator is to become increasingly accurate in distinguishing between real and fake samples.
The training process of GANs involves a competitive interplay between the generator and the discriminator. The generator tries to improve its generation process to fool the discriminator, while the discriminator tries to become more effective in identifying fake samples. This competition drives both networks to improve over time.
During training, the generator and discriminator are optimized iteratively. The generator’s objective is to generate samples that the discriminator classifies as real, while the discriminator’s objective is to correctly classify real and fake samples. The loss function used in GANs is typically the binary cross-entropy loss, where the generator and discriminator aim to minimize and maximize the loss, respectively.
The training process is typically performed using a technique called mini-batch stochastic gradient descent. In each training iteration, a mini-batch of real samples from the training dataset is randomly selected, along with an equal-sized mini-batch of generated fake samples. The discriminator is trained on this mini-batch by updating its parameters to minimize the loss. Then, the generator is trained by generating another set of fake samples and updating its parameters to maximize the loss. This iterative training process continues until the generator produces samples that are difficult for the discriminator to distinguish from real ones.
Once a GAN is trained, the generator can be used independently to generate new samples by inputting random noise. By sampling from the random noise distribution and passing it through the generator, the GAN can produce novel samples that resemble the training data.
Generative Adversarial Networks have been successful in generating realistic samples in various domains, including images, text, and audio. They have applications in image synthesis, data augmentation, style transfer, and anomaly detection, among others. However, training GANs can be challenging, as it requires balancing the learning dynamics between the generator and discriminator and addressing issues such as mode collapse and instability.