Dynamic Query as Budgeting for Tiny Object Detection

Recent DETR-based tiny object detectors adopt dynamic-query mechanisms to handle density imbalance. However, existing designs entangle two effects: how many and which queries are decoded. This entanglement obscures what actually drives the gains, thereby hindering principled dynamic-query design; additional learned predictors or heuristic filtering steps also introduce extra overhead and inevitable decision errors, which can undermine practicality and final gains. In this paper, we disentangle these effects and show that dynamic query primarily acts as budgeting---allocating decoder query capacity according to object density. Motivated by this view, we formulate a monotonic and conservative budgeting principle and propose a budgeting-based DETR (BUTR), a streamlined framework that implements dynamic query by using a lightweight, training-free budgeter to estimate an input-dependent query budget $K(x)$ from encoder confidences. BUTR applies standard Top-$K(x)$ query initialization, removing heuristic filtering, learned components, and complex selection logic. On AI-TOD-v2 and VisDrone, BUTR shows clearer density-aligned query allocation behavior than prior dynamic-query detectors and improves AP by more than 0.5, while using about half as many queries with fewer parameters and GFLOPs, requiring over 2$\times$ less training time, and delivering 4$\times$ faster inference. Additional COCO results further indicate its applicability across a broad spectrum of detection scenarios.