Reviving the Discarded High-Resolution Feature for Transformer-Based Tiny Object Detection
Authors: Zehao Wang, Si Wu, Guiping Cao, Xin Li, Yaowei Wang
Organizations: South China University of Technology, Guangzhou, China · Pengcheng Laboratory, Shenzhen, China · Harbin Institute of Technology, Shenzhen, China
Tiny object detection remains challenging because tiny instances occupy only a few pixels, and their fine-grained details are easily lost during feature downsampling. Although the highest-resolution feature preserves rich local details for tiny objects, DETR-like detectors often discard it due to its large computational cost, while directly reintroducing this feature also brings dense background noise. To address this problem, we propose ReDHF, a novel framework that Revives the Discarded High-resolution Feature for tiny object detection. ReDHF has three cooperative components. Cross-Scale Deformable Fusion (CSDF) first constructs a semantically enhanced highest-resolution feature and injects its fine-grained details into the shallow feature under a moderate cost. Ellipse-Guided Shallow Supervision (EGSS) then guides the enhanced feature to learn more reliable classification and localization priors by applying geometry-adaptive auxiliary supervision. Full-Scale Query Interaction (FSQI) further enables decoder queries to access both low-level details and high-level semantic information, allowing them to aggregate richer cues for tiny objects. Extensive experiments show that ReDHF consistently improves multiple baselines across different DETR variants and achieves state-of-the-art performance on the evaluated benchmarks. The best ReDHF variants surpass their baselines by +1.4 AP on AI-TOD-v2, +1.6 AP on VisDrone, and +1.5 AP on SODA-D, with especially notable gains on tiny and small objects.
Figures & tables
Figure 1: (a) Tiny objects may occupy only a few pixels, making their visual evidence extremely weak. (b) Very tiny objects can become nearly invisible on stride-4 feature map in the feature downsampling pipeline. (c) The ratio of ultra-tiny objects (short side ≤4 pixels) is much higher in tiny object datasets such as AI-TOD-v2, VisDrone, and SODA-D than in COCO.
Figure 2: Overview of ReDHF. CSDF revives the discarded highest-resolution feature C1 as a semantically enhanced feature P1 and injects its fine-grained details into P2 to obtain the detail-enhanced shallow feature P2′ . EGSS further supervises P2′ with ellipse-guided auxiliary supervision during training, while FSQI exposes P1 , P2′ , and deeper features to decoder queries for final detection.
Method
#Params.
GFLOPs
AP
AP 50
AP 75
AP vt
AP t
AP s
AP m
CNN-based models
Cascade R-CNN [ 1 ]
68.9M
88.7
15.1
34.2
11.2
0.1
11.5
26.7
38.5
DetectoRS [ 32 ]
134.8M
≈ 160
16.1
35.5
12.5
0.1
12.6
28.3
40.0
DetectoRS w/ RFLA [ 47 ]
–
–
24.8
55.2
18.5
9.3
24.8
30.3
38.2
YOLOv12-X [ 42 ]
59.3M
185.4
16.1
33.5
13.4
5.4
17.0
21.4
28.5
Transformer-based models
Table 1: Experiments on AI-TOD-v2 test split. All models are evaluated with 800×800 input resolution. We compare ReDHF with both CNN-based and Transformer-based detectors. † denotes our re-implementation of the corresponding baseline. ⋆ denotes the average GFLOPs measured over the whole split when the computational cost varies across images.
Baseline
VisDrone AP
VisDrone AP s
SODA-D AP
SODA-D AP eS
DINO-4scale [ 52 ]
34.3 → 35.4 (+1.1)
25.6 → 27.4 (+1.8)
28.6 → 30.1 (+1.5)
10.5 → 12.6 (+2.1)
DQ-DETR [ 15 ]
35.7 → 37.1 (+1.4)
28.2 → 29.6 (+1.4)
34.4 → 35.5 (+1.1)
17.0 → 18.5 (+1.5)
Dome-DETR-S [ 14 ]
35.9 → 37.5 (+1.6)
28.3 → 30.3 (+2.0)
35.4 → 36.8 (+1.4)
17.6 → 19.6 (+2.0)
Dome-DETR-M [ 14 ]
38.9 → 40.2 (+1.3)
31.4 → 33.1 (+1.7)
37.2 → 38.4 (+1.2)
18.6 → 20.4 (+1.8)
Dome-DETR-L [ 14 ]
39.0 → 40.6 (+1.6)
31.5 → 33.1 (+1.6)
37.6 → 38.7 (+1.1)
19.7 → 21.4 (+1.7)
Avg. gain
+1.4
+1.7
+1.3
+1.8
Table 2: Experiments on VisDrone validation split and SODA-D test split. Each entry reports baseline → ReDHF, with the gain over the corresponding baseline shown in parentheses. AP s is used as the tiny-object metric for VisDrone, and AP eS is used for SODA-D.
Table 5
Figure 3: Qualitative comparison on the AI-TOD-v2 test split. Each pair compares a baseline detector with its ReDHF variant on the same scene. The green , red , yellow , and blue boxes represent TP, FP, FN with ground-truth box short side ≤4 pixels, and the remaining FN, respectively. Compared with the baselines, ReDHF produces cleaner predictions and helps recover more tiny objects, with more green boxes and fewer red/yellow/blue boxes. Class labels are omitted for clarity.
Figure 4: Feature visualization and response analysis of CSDF. We compare C1 vs. P1 and P2 vs. P2′ . The bottom-left statistics report μin , μout , and FBR defined in Eq. 7 . After CSDF enhancement, P1 and P2′ show stronger response concentration on GT regions.
Appendix figures & tables17 assets
Supplementary material from the paper’s appendix.
Appendix
Method
#Params.
GFLOPs
Image Scale
AP
AP 50
AP 75
AP s
AP m
AP l
CNN-based models
YOLOv11 [ 17 ]
25.3M
86.6
640×640
27.9
–
–
18.1
40.9
53.1
YOLOv12 [ 42 ]
26.3M
88.6
640×640
29.2
–
–
18.7
41.8
51.7
RFLA [ 47 ]
69.2M
162.0
800×800
24.3
–
–
14.4
35.9
45.8
YOLC [ 22 ]
–
–
1024×640
39.6
–
–
32.9
49.3
56.2
CFINet [ 51 ]
41.4M
291.9
1200×1200
23.9
–
–
16.3
34.7
57.4
Appendix
Table 6: Experiments on VisDrone val split. We compare ReDHF with both CNN-based and Transformer-based detectors. † denotes our re-implementation of the corresponding baseline. ⋆ denotes the average GFLOPs measured over the whole split when the computational cost varies across images.
Method
#Params.
GFLOPs
Image Scale
AP
AP 50
AP 75
AP eS
AP rS
AP gs
AP N
CNN-based models
Faster RCNN [ 35 ]
41.2M
292.3
1200×1200
28.9
59.7
24.2
13.9
25.6
34.3
43.2
Cascade RCNN [ 1 ]
68.9M
320.1
1200×1200
31.2
59.9
27.8
14.1
27.5
37.1
46.9
RFLA [ 47 ]
41.2M
292.1
1200×1200
29.7
60.2
25.2
13.2
26.9
35.4
44.6
Transformer-based models
Deformable-DETR [ 59 ]
35.2M
739.1
1200×1200
19.2
44.8
13.7
6.3
15.4
24.9
34.2
Appendix
Table 7: Experiments on SODA-D test split. We compare ReDHF with both CNN-based and Transformer-based detectors. † denotes our re-implementation of the corresponding baseline. ⋆ denotes the average GFLOPs measured over the whole split when the computational cost varies across images.
Model
Backbone
Encoder
Decoder
Others
Whole
DINO-4scale [ 52 ]
104.5
203.9
34.9
11.1
354.4
DINO-4scale w/ direct C1
104.5 (–)
2709.5 (+2505.6)
161.0 (+126.1)
82.7 (+71.6)
3057.7 (+2703.3)
DINO-4scale w/ ReDHF
104.5 (–)
251.2 (+47.3)
40.7 (+5.8)
11.4 (+0.3)
407.8 (+53.4)
Appendix
Table 8: Computational cost comparison on DINO-4scale. We report GFLOPs of the backbone, encoder, decoder, other parts, and the whole model. “Direct C1 ” denotes directly adding the raw highest-resolution feature into the encoder and decoder. “Others” includes components not counted in the backbone, encoder, or decoder.
Model
Input
GFLOPs
AP
AP vt
DINO-4scale
800
354.4
25.1
12.1
DINO-4scale
864
412.4
25.4
12.4
DINO-4scale w/ ReDHF
800
407.8
26.0
13.8
Dome-DETR-L
800
358.7
34.6
19.6
Dome-DETR-L
880
481.1
35.0
20.0
Dome-DETR-L w/ ReDHF
800
415.3
35.7
20.8
Appendix
Table 9: Compute-matched comparison with input-resolution scaling on AI-TOD-v2. We increase only the input resolution of the baselines while keeping the detector and training settings unchanged. The best result within each baseline family is highlighted in bold.
Dataset
Variant
Tiny AP ↑
Latency (ms) ↓
Avg. memory (GiB) ↓
Peak memory (GiB) ↓
AI-TOD-v2
Dome-DETR-S
17.5 → 18.9
409.6 → 507.6
0.30 → 0.56
0.63 → 1.72
Dome-DETR-M
18.9 → 20.7
450.0 → 578.0
0.39 → 0.65
0.77 → 1.86
Dome-DETR-L
19.6 → 20.8
487.8 → 655.2
0.47 → 0.76
0.86 → 1.99
VisDrone
Dome-DETR-S
28.3 → 30.3
454.5 → 584.1
0.27 → 0.46
0.63 → 1.72
Dome-DETR-M
31.4 → 33.1
512.8 → 680.1
0.36 → 0.57
0.77 → 1.86
Dome-DETR-L
31.5 → 33.1
543.5 → 751.8
0.47 → 0.69
0.88 → 2.01
Appendix
Table 10: Practical inference cost of ReDHF on AI-TOD-v2 and VisDrone. Wall-clock latency and GPU memory are measured on a single Tesla V100 with batch size 1 under identical baseline and ReDHF settings. Each entry reports baseline → ReDHF. Tiny AP denotes AP vt on AI-TOD-v2 and AP s on VisDrone.
Dataset
Smallest objects
Intermediate objects
Larger objects
AI-TOD-v2
AP vt +1.48
AP t +0.86
AP s +0.40, AP m +0.00
VisDrone
AP s +1.70
AP m +0.86
AP l +0.32
SODA-D
AP eS +1.82
AP rS +1.26
AP gS +0.82, AP N +0.40
Appendix
Table 11: Scale-wise performance gains of ReDHF averaged over the five evaluated DETR variants. The dataset-specific metrics are ordered from smaller to larger object scales.
Model
AP
AP s
AP m
AP l
DINO-4scale
49.0
32.0
52.3
63.0
DINO-4scale w/ ReDHF
49.6 (+0.6)
32.6 (+0.6)
53.1 (+0.8)
63.5 (+0.5)
Appendix
Table 12: Generalization of ReDHF on COCO using DINO-4scale. Both models use the same 12-epoch training recipe.
Variant
Sparse AP s
Sparse AP m
Sparse AP l
Dense AP s
Dense AP m
Dense AP l
Dome-DETR-S
28.24 → 30.31 ( +2.07 )
47.09 → 48.91 ( +1.82 )
60.60 → 63.12 ( +2.52 )
28.11 → 30.58 ( +2.47 )
44.76 → 45.96 ( +1.20 )
57.15 → 55.60 (-1.55)
Dome-DETR-M
30.86 → 33.02 ( +2.16 )
50.80 → 51.10 ( +0.30 )
64.86 → 65.13 ( +0.27 )
32.02 → 33.46 ( +1.44 )
48.46 → 49.41 ( +0.95 )
60.76 → 59.80 (-0.96)
Dome-DETR-L
31.54 → 32.90 ( +1.36 )
50.12 → 52.09 ( +1.97 )
68.34 → 68.86 ( +0.52 )
31.71 → 33.37 ( +1.66 )
49.15 → 50.40 ( +1.25 )
55.60 → 56.62 ( +1.02 )
Appendix
Table 13: Density-wise analysis on the VisDrone validation set. Images are ranked by the number of annotated instances and divided into two equally sized sparse and dense subsets. Each entry reports baseline → ReDHF, with the absolute change in parentheses.
Assignment strategy
AP
AP 50
AP 75
AP vt
AP t
AP s
AP m
Rectangle-based
33.2
66.9
28.7
17.6
33.0
38.2
45.0
Short-axis circle-based
33.3
67.8
28.4
18.1
32.9
38.4
46.1
Ellipse-guided (ours)
33.5
68.1
28.9
18.9
33.5
38.7
45.8
Appendix
Table 14: Comparison of different label assignment strategies for EGSS. The best result in each column is highlighted in bold.
Inject layer
AP
AP 50
AP 75
AP vt
AP t
AP s
AP m
P2∼P3
32.8
66.5
28.1
18.0
32.7
38.5
45.0
P2∼P5
32.4
66.3
27.3
18.3
32.2
38.2
44.6
P2 only
33.5
68.1
28.9
18.9
33.5
38.7
45.8
Appendix
Table 15: Ablation on the detail injection level. We keep other components unchanged and only vary the target feature levels. The best result in each column is highlighted in bold.
Aggregation mode
Params
GFLOPs
AP
AP 50
AP 75
AP vt
AP t
AP s
AP m
Bilinear
15.88
182.3
29.4
61.9
24.0
14.9
29.4
36.6
41.5
AvgPool
15.88
182.3
33.1
66.9
28.7
18.4
32.9
38.8
45.0
Strided Conv
15.95
187.5
32.8
66.7
27.9
18.1
32.8
38.0
44.7
Deform. Cross-Attn
15.93
188.2
33.5
68.1
28.9
18.9
33.5
38.7
45.8
Appendix
Table 16: Comparison of different strategies for downsampling P1 to the P2 resolution in CSDF. We keep the semantically enhanced P1 and other ReDHF components unchanged, and only vary the strategies. The best result in each column is highlighted in bold.
Aggregation
μin(P2′)
μout(P2′)
FBR (P2′)
FBR (P2)
Δ FBR
AP vt
Bilinear
0.49
0.33
1.48
1.44
0.04
14.9
AvgPool
0.45
0.27
1.67
1.45
0.22
18.4
Strided Conv
0.52
0.32
1.63
1.45
0.18
18.1
Deformable cross-attn
0.57
0.31
1.84
1.46
0.38
18.9
Appendix
Table 17: Foreground-to-background response analysis for different downsampling strategies in CSDF. Δ FBR denotes the increase from P2 to P2′ . The best result in each column is highlighted in bold.
Figure 5: Sensitivity analysis of the sampling-point numbers in CSDF and FSQI. The bottom x-axis shows the number of sampling points, the top x-axis shows the corresponding GFLOPs. The left y-axis reports AP, while the right y-axis reports APvt . In the left subplot, we vary the CSDF points while fixing the FSQI points to 8. In the right subplot, we vary the FSQI points while fixing the CSDF points to 8.
Dataset
Baseline AP / Tiny AP
GT coverage @8 / @16 (%)
AP / Tiny AP @8
AP / Tiny AP @16
Default rmax
AI-TOD-v2
32.1 / 17.5
98.17 / 100.00
33.5 / 18.9
33.4 / 18.7
8
VisDrone
35.9 / 28.3
64.14 / 90.28
37.1 / 29.8
37.5 / 30.3
16
SODA-D
35.4 / 17.6
73.69 / 100.00
36.6 / 19.3
36.8 / 19.6
16
Appendix
Table 18: Sensitivity to the scale threshold rmax in EGSS. GT coverage denotes the percentage of valid ground-truth instances selected for supervising P2′ under the corresponding threshold. Tiny AP denotes AP vt , AP s , and AP eS on AI-TOD-v2, VisDrone, and SODA-D, respectively. The adopted setting for each dataset is highlighted in bold.
Setting
λcls
λreg
AP
AP 50
AP vt
AP t
AP s
cls only
1.0
–
33.2
68.2
18.1
33.2
38.5
cls + reg
1.0
0.10
33.5
68.1
18.9
33.5
38.7
cls + reg + ctr
1.0
0.10
32.1
66.5
15.8
32.2
38.2
cls + reg
1.0
0.05
33.3
67.1
18.7
33.3
39.2
1.0
0.20
33.1
67.2
17.6
33.7
38.6
1.0
0.50
32.8
67.7
17.3
32.3
38.6
Appendix
Table 19: Ablation study on the EGSS loss design. The centerness loss weight is set to 0.1 when used. The best result is highlighted in bold.
Table 23
Scale
Num. GT
Avg. Npos
Npos≤2 (%)
Avg. Nc≥0.5
Nc≥0.5≤1 (%)
Very tiny
47317
1.90
78.26
0.54
93.90
Tiny
276865
6.44
23.69
1.79
33.76
Small
45612
19.19
3.18
5.21
1.57
Medium
6782
81.05
0.13
21.59
0.93
Appendix
Table 22: Statistics of centerness targets across object scales on AI-TOD-v2. Npos denotes the number of positive feature locations assigned to each ground-truth instance, and Nc≥0.5 denotes the number of positive locations whose centerness target is at least 0.5.
Small object detection remains a significant challenge due to feature degradation from downsampling, mutual occlusion in dense clusters, and complex background interference. To address these issues, this paper proposes FSDETR, a frequency-spatial feature enhancement framework built upon the RT-DETR baseline. By establishing a collaborative modeling mechanism, the method effectively leverages complementary structural information. Specifically, a Spatial Hierarchical Attention Block (SHAB) captures both local details and global dependencies to strengthen semantic representation. Furthermore, to mitigate occlusion in dense scenes, the Deformable Attention-based Intra-scale Feature Interaction (DA-AIFI) focuses on informative regions via dynamic sampling. Finally, the Frequency-Spatial Feature Pyramid Network (FSFPN) integrates frequency filtering with spatial edge extraction via the Cross-domain Frequency-Spatial Block (CFSB) to preserve fine-grained details. Experimental results show that with only 14.7M parameters, FSDETR achieves 13.9% APS on VisDrone 2019 and 48.95% AP50 tiny on TinyPerson, showing strong performance on small-object benchmarks. The code and models are available at https://github.com/YT3DVision/FSDETR.
Jianchao Huang, Fengming Zhang, Haibo Zhu +1
School of Artificial Intelligence and Computer Science, Jiangnan University, Wuxi, China
YOLO-series and DETR-based detectors struggle with tiny-object detection. YOLO-style models benefit from efficient dense prediction, but their large-stride backbones may suppress tiny instances in deep feature maps and make grid assignment ambiguous. DETR-based models remove hand-crafted post-processing through set prediction, yet they reason over coarse token grids, where tiny objects occupy only a few weak tokens and are easily overlooked during matching. To address these limitations, we propose TinyFormer, a unified YOLO--DETR hybrid real-time detector that combines ViT representations, NMS-free set prediction, and a YOLO-style pyramid neck for accurate small-object detection. TinyFormer introduces a Parallel Bi-fusion Module (PBM), which builds high-resolution shortcuts from shallow stages to the feature pyramid, preserving fine spatial details during multi-scale fusion. We further design a Spatial Semantic Adapter (SSA) to compensate for the spatial loss caused by coarse tokenization. SSA extracts high-resolution cues from early stages and injects them into transformer token embeddings, improving tiny-object localization without sacrificing the global modeling ability of DETR. Experiments on MS COCO show that TinyFormer consistently outperforms recent YOLO-series detectors and the strong DEIMv2 baseline. TinyFormer-X achieves 58.4% AP even without PBM, while adding PBM improves the overall AP to 58.5% and brings a 1.6% AP gain on small objects. With Objects365 pre-training, TinyFormer-X-PBM reaches 60.2% AP, surpassing RF-DETR and other Objects365-pretrained detectors with fewer parameters and lower computation. These results demonstrate that TinyFormer bridges dense YOLO-style feature fusion and DETR-style set prediction, providing a strong accuracy-efficiency trade-off for real-time tiny-object detection. Code is available at https://github.com/mmpmmpmmpjosh/TinyFormer.
Ultra-High-Resolution (UHR) imagery has become essential for modern remote sensing, offering unprecedented spatial coverage. However, detecting small objects in such vast scenes presents a critical dilemma: retaining the original resolution for small objects causes prohibitive memory bottlenecks. Conversely, conventional compromises like image downsampling or patch cropping either erase small objects or destroy context. To break this dilemma, we propose UHR-DETR, an efficient end-to-end transformer-based detector designed for UHR imagery. First, we introduce a Coverage-Maximizing Sparse Encoder that dynamically allocates finite computational resources to informative high-resolution regions, ensuring maximum object coverage with minimal spatial redundancy. Second, we design a Global-Local Decoupled Decoder. By integrating macroscopic scene awareness with microscopic object details, this module resolves semantic ambiguities and prevents scene fragmentation. Extensive experiments on the UHR imagery datasets (e.g., STAR and SODA-A) demonstrate the superiority of UHR-DETR under strict hardware constraints (e.g., a single 24GB RTX 3090). It achieves a 2.8% mAP improvement while delivering a 10× inference speedup compared to standard sliding-window baselines on the STAR dataset. Our codes and models will be available at https://github.com/Li-JingFang/UHR-DETR.
Jingfang Li, Haoran Zhu, Wen Yang +4
School of Electronic Information, Wuhan University, Wuhan, 430072 China