Can Frozen Hyperspherical Features Guide the Selection of Pseudo Masks?
Organizations: Duke University · Carnegie Mellon University · University of Alabama at Birmingham
Abstract
Foundation segmenters such as SAM return several plausible masks for an unlabeled image, and a student trained on the wrong one inherits its errors. Choosing among them means querying a second large model or fitting a quality head to annotated masks. We show that a candidate can be judged by what it does to a frozen self-supervised backbone's features. Normalized DINOv2 patch features lie on a hypersphere, and a candidate mask splits that sphere in two. Based on this reading, we introduce SphereTrust, which scores each candidate by three properties of the split, the angular contrast between the two sides, the coverage of the foreground's appearance modes, and contact with the image frame, one for each of three common ways a mask fails, and ranks a pool in 0.55 s per image from the frozen features alone. On eight SAM and SAM3 candidate pools spanning camouflaged, salient, and dichotomous segmentation and camouflage under low light, SphereTrust exceeds the strongest evaluated external baseline on six pools by 1.7 to 9.3 percentage points in mean selected Dice. These comparisons include published selection rules and explicitly labeled adaptations of DSS and UCOD-MKD. On the two prompted camouflage pools, its mean selected Dice is within 0.1 percentage points of the candidate-derived DSS adaptation, with a lower catastrophic-error rate. Which cue carries the signal depends on the candidate pool. The same sphere also supports training. The leading candidates enter as a candidate set with their scores as priors, prototypes reorder them, and a cross-fitted second round completes the labels, raising weighted F by 4.5, 2.3, and 5.5 points over fixed-label training on the three MLLM anchor pools, with students competitive with published unsupervised methods on nineteen test sets.
Figures & tables
| Selector | SAM3 alone | MLLM anchor SAM | ||
|---|---|---|---|---|
| COD | COD | SOD | DIS | |
| each entry: sel-Dice / Top-1 / Dice .2 | ||||
| Random | .657/.096/.193 | .678/.057/.170 | .771/.045/.111 | .576/.047/.204 |
| SelfMask vote ( Shin et al., 2022 ) | .821 /.124/ .062 | .778 /.060/ .085 | .887/.034/.024 | .701/.060/ .086 |
| SAQ ( Lin et al., 2024 ) | .576/.109/.275 | .676/.098/.184 | .771/.163/.125 | .606/.117/.187 |
| Generator confidence ( Carion et al., 2025 ) | .802/.145/.082 | .728/.057/.135 | .874/.033/.040 | .636/.060/.179 |
| COD | SOD | DIS | |||
| random candidate | .6780 | .7709 | .5762 | ||
| oracle candidate | .8517 | .9486 | .8385 | ||
| ✓ | ✗ | ✗ | .7663 | .8789 | .6351 |
| ✗ | ✓ | ✗ | .6587 | .8894 | .6761 |
| ✗ | ✗ | ✓ | .7490 | .8269 | .6108 |
| ✓ | ✓ | ✗ | .7546 | .9280 | .7356 |
| Method | MAE | |||
|---|---|---|---|---|
| Camouflage COD10K, | ||||
| EReCu ( Jiang et al., 2026 ) † | .7221 | .5628 | .8185 | .0613 |
| FOUND ( Siméoni et al., 2023 ) † | .6783 | .5056 | .6475 | .0841 |
| TokenCut ( Wang et al., 2022b ) † | .6638 | .4770 | .7539 | .1023 |
| UCOD-DPL (DINOv2) ( Yan et al., 2025 ) † | .8340 | .7630 | .9160 | .0310 |
| UCOD-MKD (PVTv2) ( Chen et al., 2026 ) † | .8350 | .7400 | .9080 | .0310 |
Appendix figures & tables17 assets
Supplementary material from the paper’s appendix.
Appendix
| selection pool (Tab. ) | training pool (Tab. ) | |||||||
| regime | random | oracle | random | oracle | ||||
| Camouflage | 1979 | 10.2 | .1319 | .6770 | 3857 | 25.6 | .6780 | .8517 |
| Salient | 4993 | 10.7 | .1697 | .7878 | 4025 | 25.0 | .7709 | .9486 |
| Dichotomous | 465 | 11.3 | .0992 | .4856 | 2969 | 28.4 | .5762 | .8385 |
| Low light | 1932 | 9.4 | .1307 | .6028 | direct camouflage evaluation | |||
| pool family | datasets | images | candidates | selected Dice [95% CI] |
|---|---|---|---|---|
| unprompted SAM macro | 4 | |||
| prompted SAM macro | 3 | |||
| non-SAM pool | 4 |
| Selector | COD | SOD | DIS | LL |
|---|---|---|---|---|
| COD10K | DUTS-TE | DIS-VD | LL-COD | |
| each entry: sel-Dice / Top-1 / Dice .2 | ||||
| Random | .132/.162/.821 | .170/.129/.743 | .099/.120/.824 | .131/.183/.813 |
| SelfMask vote ( Shin et al., 2022 ) | .218/.221/.723 | .348/.274/.534 | .133/.110/.757 | .203/.219/.731 |
| SAQ ( Lin et al., 2024 ) | .102/.133/.855 | .141/.098/.777 | .072/.067/.867 | .082/.131/.876 |
| SAM predicted IoU ( Kirillov et al., 2023 ) | .256/.303/.693 | .285/.264/.650 | .096/.131/.843 | .201/.271/.741 |
| COD | SOD | DIS | ||||
| per seed | per seed | per seed | ||||
| selection only (fixed rank one label) | .7513 .0004 | / / | .8148 .0033 | / / | .6048 .0018 | / / |
| candidate set training (round one) | .7930 .0006 | / / | .8232 .0031 | / / | .6384 .0026 | / / |
| second round (full method) | .7961 .0007 | .8376 .0013 | .6594 .0014 | |||
| full method without | ||||||
| completed mask | .7941 .0002 | / / | .8209 .0010 | / / | .6434 .0010 | / / |
| validation | test regime mean | ||||||
| configuration | COD | SOD | DIS | mean | COD | SOD | DIS |
| round one | |||||||
| order by , argmax rule | .7701 | .9377 | .7580 | .8219 | .7873 | .8210 | .6377 |
| order by , softmax weights | .7675 | .9400 | .7549 | .8208 | .7841 | .8181 | .6371 |
| order by , argmax rule (chosen) | .7759 | .9392 | .7544 | .8232 | .7955 | .8185 | .6372 |
| second round | |||||||
| CAMO, | CHAMELEON, | NC4K, | ||||||||||
| Method | MAE | MAE | MAE | |||||||||
| EASE (DINO ViT-S/8) ( Du et al., 2025a ) † | .6530 | .5630 | .7370 | .1660 | .6760 | .5500 | .7650 | .1050 | .7280 | .6330 | .7900 | .1080 |
| EASE (DINOv2 ViT-L/14) ( Du et al., 2025a ) † | .7490 | .6840 | .8310 | .0980 | .8190 | .7410 | .8990 | .0440 | .8000 | .7350 | .8840 | .0560 |
| RISE (DINOv2 ViT-L/14) ( Du et al., 2025b ) † | .7340 | .6100 | .7870 | .1090 | .8220 | .7200 | .8840 | .0500 | .8050 | .7050 | .8680 | .0610 |
| RISE (SAM ViT-H masks) ( Du et al., 2025b ) † | .7600 | .6510 | .8070 | .1020 | .8230 | .7330 | .8820 | .0550 | .8250 | .7360 | .8740 | .0560 |
| DualUCOD (DINOv2) ( Liu et al., 2026 ) † | .7710 | .7020 | .8520 | .0830 | .8270 | .7540 | .9180 | .0410 | .8080 | .7450 | .8960 | .0520 |
| DUTS-TE | ECSSD | HKU-IS | DUT-OMRON | PASCAL-S | |||||||||||
| Method | MAE | MAE | MAE | MAE | MAE | ||||||||||
| A2S-v3 ( Yuan et al., 2024 ) † | .0470 | .8160 | .9060 | .0380 | .9230 | .9510 | .0330 | .9080 | .9540 | .0620 | .7590 | .8680 | .0690 | .8440 | .8990 |
| DCFD ( Lin et al., 2022 ) † | .0640 | .7640 | .8550 | .0590 | .8880 | .9150 | .0420 | .8890 | .9350 | .0700 | .7100 | .8370 | .0900 | .7950 | .8600 |
| EDNS ( Zhang et al., 2020 ) † | .0650 | .7350 | .8470 | .0680 | .8720 | .9060 | .0460 | .8740 | .9330 | .0760 | .6820 | .8210 | .0970 | .8010 | .8460 |
| STC ( Song et al., 2023 ) † | .0520 | .8090 | .8910 | .0500 | .9030 | .9350 | .0410 | .8910 | .9420 | .0680 | .7530 | .8520 | .0760 | .8270 | .8810 |
| SelfMask ( Shin et al., 2022 ) † | .0630 | .7140 | .8480 | .0580 | .8560 | .9200 | .0530 | .8190 | .9150 | .0780 | .6680 | .8150 | .0870 | .7740 | .8560 |
| DUTS-TE | ECSSD | HKU-IS | DUT-OMRON | PASCAL-S | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Method | ||||||||||
| 3SD ( Yasarla et al., 2024 ) | .8121 | .6370 | .8848 | .7907 | .8774 | .7662 | .7979 | .6187 | .8060 | .6859 |
| CutLER ( Wang et al., 2023 ) | .6503 | .5149 | .7897 | .7426 | .7686 | .7005 | .6092 | .4660 | .7275 | .6574 |
| FOUND ( Siméoni et al., 2023 ) | .8029 | .7479 | .8691 | .8708 | .7959 | .7810 | .7709 | .6793 | .8075 | .7838 |
| UMNet ( Wang et al., 2022c ) | .8027 | .7039 | .8677 | .8391 | .8865 | .8561 | .8047 | .6972 | – | – |
| Selfment ( You et al., 2026 ) | .7977 | .5659 | .8790 | .7194 | .8700 | .6966 | .7141 | .4284 | .8219 | .6500 |
| Method | MAE | mDice | |||
|---|---|---|---|---|---|
| DIS-TE1 , | |||||
| Selfment ( You et al., 2026 ) | .7054 | .3870 | .6628 | .1445 | .5061 |
| A2S-v3 ( Yuan et al., 2024 ) | .6028 | .4105 | .6887 | .1379 | .4683 |
| CSNet-crf ( Guan et al., 2025 ) | .5828 | .3625 | .6645 | .1171 | .3996 |
| SPHERETRUST , MLLM anchor | .7765 | .6463 | .8324 | .0699 | .6866 |
| DIS-TE2 , | |||||
| pool | student, mean of four COD sets | |||||
|---|---|---|---|---|---|---|
| pool | oracle | selected | MAE | |||
| MLLM anchor SAM | .858 | .790 | .8643 | .7961 | .9146 | .0395 |
| SAM3 alone | .895 | .829 | .8710 | .8086 | .9257 | .0342 |
| COD | SOD | DIS | |||||||
|---|---|---|---|---|---|---|---|---|---|
| ranking rule | sel | fixed | full | sel | fixed | full | sel | fixed | full |
| SPHERETRUST | .787 | .7526 .0004 | .7971 .0009 | .929 | .8144 .0006 | .8403 .0009 | .771 | .6047 .0013 | .6597 .0010 |
| size control | .763 | .7287 .0009 | .7958 .0005 | .909 | .8009 .0019 | .8367 .0004 | .755 | .5842 .0009 | .6571 .0008 |
| adapted DSS | .788 | .7624 .0011 | .7953 .0016 | .912 | .7918 .0012 | .8303 .0018 | .720 | .5464 .0032 | .6529 .0011 |
| COD | SOD | DIS | |||||||
|---|---|---|---|---|---|---|---|---|---|
| comparator | s0 | s1 | s2 | s0 | s1 | s2 | s0 | s1 | s2 |
| size control | |||||||||
| adapted DSS | |||||||||
| Selector | camouflage | salient | dichotomous | |
|---|---|---|---|---|
| PlantCamo | SOD300 | MSRA-B | UHRSD | |
| , | , | , | , | |
| Random | .434 | .555 | .747 | .676 |
| SelfMask vote | .505 | .611 | .873 | .789 |
| SAQ | .433 | .519 | .769 | .683 |
| SAM predicted IoU | .474 | .625 | .856 | .770 |
| student | MAE | |||
|---|---|---|---|---|
| camouflage students , PlantCamo-TE | ||||
| full method, MLLM anchor | .686 | .515 | .763 | .097 |
| full method, SAM3 pool | .621 | .422 | .682 | .110 |
| selection only, MLLM anchor | .681 | .499 | .755 | .101 |
| salient student , SOD300 | ||||
| full method | .765 | .736 | .797 | .116 |