FreeStyle: Toward Style-Inclusive Sketch-Based Person Retrieval.

Abstract

Sketch-based Person Retrieval (SBPR) aims to identify and retrieve a target individual across non-overlapping camera views using professional sketches as queries. In practice, sketches drawn by different artists often present diverse painting styles unpredictably. The substantial style variations among sketches pose significant challenges to the stability and generalizability of SBPR models. Prior works attempt to mitigate style variations through style manipulation methods, which inevitably undermine the inherent structural relations among multiple sketch features. This leads to overfitting on existing training styles and struggles with generalizing to new, unseen sketch styles. In this paper, we introduce FreeStyle, an innovative style-inclusive framework for SBPR, built upon the foundational CLIP architecture. FreeStyle explicitly models the relations across diverse sketch styles via style consistency enhancement, enabling dynamic adaptation to both seen and unseen style variations. Specifically, Diverse Style Semantic Unification is first devised to enhance the style consistency of each identity at the semantic level by introducing objective attribute-level semantic constraints. Meanwhile, Diverse Style Feature Squeezing tackles unclear feature boundaries among identities by concentrating the intra-identity space and separating the inter-identity space, thereby strengthening style consistency at the feature representation level. Additionally, considering the feature distribution discrepancy between sketches and photos, an identity-centric cross-modal prototype alignment mechanism is introduced to facilitate identity-aware cross-modal associations and promote a compact joint embedding space. Extensive experiments validate that FreeStyle not only achieves stable performance under seen style variations but also demonstrates strong generalization to unseen sketch styles.