Training-Free Fine-Grained Semantic Segmentations in Low Data Regimes: A FungiTastic Baseline
This work addresses the challenges of precise localization and discrimination among visually similar classes in fine-grained semantic segmentation under low-data regimes, particularly for fungal images exhibiting long-tailed distributions and varying acquisition conditions. To tackle these issues, the authors propose a training-free, two-stage decoupled framework: first, category-agnostic masks are generated using SAM3 guided by coarse-class prompts; then, fine-grained labels are assigned via prototype matching in the DINOv2 embedding space, augmented with simple feature-space transformations to enhance classification performance. This approach establishes the first effective baseline for low-data fine-grained segmentation, demonstrating superior performance across settings ranging from one-shot to hundreds of samples, while offering strong scalability and low computational cost.