Towards Realistic Zero-Shot Classification via Self Structural Semantic Alignment

TL;DR

This paper introduces S^3A, a novel framework for realistic zero-shot classification that leverages structural semantic information from unlabeled data and self-learning to improve accuracy without relying on annotated datasets.

Contribution

The paper proposes the S^3A framework with the CVPR algorithm for extracting and aligning structural semantics, enabling zero-shot classification in open-world scenarios without annotations.

Findings

Achieves over 15% accuracy improvement over CLIP on average.

Effectively extracts structural semantics from unlabeled data.

Demonstrates superior performance across various benchmarks.

Abstract

Large-scale pre-trained Vision Language Models (VLMs) have proven effective for zero-shot classification. Despite the success, most traditional VLMs-based methods are restricted by the assumption of partial source supervision or ideal vocabularies, which rarely satisfy the open-world scenario. In this paper, we aim at a more challenging setting, Realistic Zero-Shot Classification, which assumes no annotation but instead a broad vocabulary. To address this challenge, we propose the Self Structural Semantic Alignment (S^3A) framework, which extracts the structural semantic information from unlabeled data while simultaneously self-learning. Our S^3A framework adopts a unique Cluster-Vote-Prompt-Realign (CVPR) algorithm, which iteratively groups unlabeled data to derive structural semantics for pseudo-supervision. Our CVPR process includes iterative clustering on images, voting within each cluster to identify initial class candidates from the vocabulary, generating discriminative prompts with large language models to discern confusing candidates, and realigning images and the vocabulary as structural semantic alignment. Finally, we propose to self-learn the CLIP image encoder with both individual and structural semantic alignment through a teacher-student learning strategy. Our comprehensive experiments across various generic and fine-grained benchmarks demonstrate that the S^3A method offers substantial improvements over existing VLMs-based approaches, achieving a more than 15% accuracy improvement over CLIP on average. Our codes, models, and prompts are publicly released at https://github.com/sheng-eatamath/S3A.