What is Open Set Recognition

Understanding Open Set Recognition in AI


Artificial intelligence has become an essential tool for businesses, organizations, and governments alike. It has the potential to transform the way we live, work, and interact with the world around us. However, achieving robust AI is a challenging task, especially in the field of computer vision. One of the key challenges in computer vision is the open set recognition problem.

The open set recognition problem is the task of detecting novel objects in a scene that have not been seen during training. This is a critical problem as it impacts the real-world applicability of AI systems. If AI systems are only designed to recognize known objects, they are unlikely to provide adequate solutions in applications where new objects may be encountered frequently.

In this article, we will explore open set recognition, its challenges, and some of the approaches that have been proposed to address this problem.

The Challenge of Open Set Recognition

The open set recognition problem arises because AI models are often trained on a finite set of classes. The number of classes that can be recognized depends on the size and quality of the training dataset and the complexity of the model. However, in many real-world applications, the number of possible object classes is infinite.

For instance, consider the task of detecting pedestrians on a road using AI. During training, the AI model may be trained on a finite set of images of pedestrians from a specific camera angle and in a particular pose. However, during deployment, the model may encounter pedestrians from various angles, postures, and clothing styles that it has not seen before. In such cases, the model would struggle to recognize the pedestrians correctly.

Another challenge in open set recognition is the fact that novel objects may have different characteristics than known objects. For instance, a known object class may be defined by its texture, shape, or color. However, novel objects may not follow these properties.

To improve the robustness of AI systems, it is crucial to address the open set recognition problem.

Approaches to Address Open Set Recognition

Several approaches have been proposed to resolve the open set recognition problem. Here are some of them:

  • Thresholding-based methods: These methods classify a test image as known or unknown based on a confidence score threshold. If the confidence score of the image is above the threshold, it is classified as known; otherwise, it is considered unknown. These methods work best when the probabilities of known objects are clustered together, and the probability distribution of unknown objects is different from that of known objects.
  • Detector-based methods: These methods combine a detector for known objects with a separate detector for unknown objects. During testing, the input image is passed through both detectors simultaneously. If no known objects are detected, the input image is classified as unknown. These methods work well in scenarios where the unknown objects are rare and have distinct visual characteristics.
  • Generative modeling: These methods generate synthetic samples of novel objects based on the known classes in the training data. The generated samples are then used to fine-tune a pre-trained AI model, thereby improving its ability to recognize novel objects. These methods work best when the known object classes have high variability and can be used to generate a wide range of novel objects.
  • Representation-based methods: These methods learn a compact and discriminative representation of known objects that can be used to recognize novel objects. During training, these methods learn a feature extraction network and a classifier network, both of which are optimized to handle known objects. During testing, the feature extraction network is used to extract features from images, while a thresholding-based method or a detector-based method is used for decision-making.


The open set recognition problem is a critical challenge that must be addressed to enable AI systems to operate robustly in real-world applications. Several approaches have been proposed to address this problem, and each approach has its advantages and limitations. As AI technology progresses, it is likely that new techniques will be developed that can better handle the open set recognition problem.