Siamese Networks

Siamese Networks

Siamese Networks are a class of neural networks that are specialized for tasks involving comparison or verification between two comparable items. They are particularly useful in applications such as face recognition, signature verification, and anomaly detection, where the objective is to learn a similarity function that measures how similar or different two inputs are.


A Siamese Network is a type of artificial neural network that contains two or more identical subnetworks, which have the same configuration and share the same parameters and weights. These subnetworks are trained simultaneously, and their outputs are compared to determine the similarity between the inputs.

How Siamese Networks Work

Siamese Networks consist of two identical neural networks, each taking one of the two input vectors. The last layers of these networks are then fed into a contrastive loss function, which calculates the similarity between the two inputs. This similarity score can then be used to determine whether the inputs belong to the same class or not.

The key feature of Siamese Networks is that they share the same weights while comparing two different inputs. This allows the network to effectively learn the similarity function from the data, as it is exposed to pairs of inputs and learns to recognize their similarities and differences.

Applications of Siamese Networks

Siamese Networks are widely used in tasks that involve comparing two inputs. Some of the most common applications include:

  • Face Recognition: Siamese Networks are often used in face recognition systems, where the task is to verify whether two images belong to the same person. The network learns to recognize the unique features of each individual’s face and can then compare these features to determine whether two images are of the same person.

  • Signature Verification: In signature verification, the goal is to determine whether two signatures belong to the same person. Siamese Networks can learn the unique characteristics of a person’s signature and compare these characteristics to verify the authenticity of a signature.

  • Anomaly Detection: Siamese Networks can also be used in anomaly detection, where the task is to identify unusual or suspicious behavior. The network is trained on pairs of normal behavior, and can then compare new behavior to this learned normal behavior to detect anomalies.

Advantages and Disadvantages of Siamese Networks

Siamese Networks offer several advantages over traditional neural networks. They are particularly effective at tasks involving comparison or verification, as they can learn a similarity function directly from the data. They also require less data than traditional networks, as they can learn from pairs of inputs rather than individual inputs.

However, Siamese Networks also have some disadvantages. They can be more complex and computationally intensive than traditional networks, as they involve training two identical networks simultaneously. They also require pairs of inputs for training, which can be more difficult to obtain in some cases.

Further Reading

For more in-depth information on Siamese Networks, consider the following resources:

  • Neural Networks
  • Contrastive Loss Function
  • Face Recognition
  • Signature Verification
  • Anomaly Detection