---
license: mit
pipeline_tag: image-segmentation
tags:
  - vesuvius
  - herculaneum
  - fibers
  - computed-tomography
  - 3d-segmentation
  - dino-guided
  - self-distillation
  - self-supervised
  - volumetric-imaging
---

# PHerc. Paris 4 — 2-class fiber segmentation, DINO-embedding-guided self-training (step 10000)

Segments **fiber vs. background** (2 classes — not an orientation split, see
below) in 3D, directly in micro-CT of **PHerc. Paris 4**, trained with **no
fixed ground truth**: a pseudo-label is regenerated every step from a frozen
teacher UNet's own predictions, adaptively thresholded and refined against a
DINO-embedding similarity map.

**This is a precursor / component checkpoint, not villa's flagship 4-class
fiber/ink model.** It is published because it is real, verified lineage: per
villa's own [`scripts/fiber_5class/train.py`](https://github.com/ScrollPrize/villa/blob/main/scripts/fiber_5class/train.py)
(PR [#985](https://github.com/ScrollPrize/villa/pull/985)) module docstring,
*this exact checkpoint* — referred to there by its W&B run ID, "ihoo3tpl ckpt"
— is loaded as the frozen **fiber teacher** input to villa's separate, later,
4-class (background / vertical fiber / horizontal-angular fiber / ink)
self-distillation trainer. See **Relationship to the 4-class model** below;
we do not currently have that 4-class model's weights to publish.

## Model details

| | |
|---|---|
| Architecture | `vesuvius` `NetworkFromConfig` 3D UNet (`shared_encoder` / `shared_decoder` / `task_heads`, the same family used across villa's segmentation models), single `fibers` head |
| Output | **2 channels**, softmax. Channel 0 = background, channel 1 = fiber foreground — confirmed via villa's own `label_generator.py::_to_fg_prob`, the function that loads this exact checkpoint as a frozen teacher (2-channel case: `softmax(logits, dim=1)[:, 1:2]`) |
| Input | 1-channel CT, 256³ patches |
| This checkpoint | step **10000** · W&B run [`ps256_fiber_dinoguided__dino362500__cls3__embbackbone__ddp8__20260522`](https://wandb.ai/vesuvius-challenge/vesuvius_fibers_3d/runs/ihoo3tpl) (`ihoo3tpl`, project `vesuvius_fibers_3d`, state **finished**) |
| Weights | `model` (raw) and `ema` (**EMA — recommended for inference**, decay 0.9995) |
| Optimisation | SGD + Nesterov (lr 0.005, momentum 0.99, weight_decay 3e-5), cosine LR, 1500-step warmup, bf16 mixed precision, BCE + soft Dice (0.1 label smoothing each), batch size 2 × 8 GPUs (`ddp8`), 12000 total iterations |
| Trained on | PHerc. Paris 4, 2.4 µm scan (`s3://vesuvius-challenge-open-data/PHercParis4/volumes/20260411134726-2.400um-0.2m-78keV-masked.zarr/`) |

## Training procedure: DINO-embedding-guided dynamic pseudo-labeling

Unlike a conventional teacher→student distillation with a fixed label set,
this run generates a **new pseudo-label every step** from:

1. A frozen self-trained fiber UNet's own probability map —
   [`scrollprize/fiber_selftrain_teacher_epoch30`](https://huggingface.co/scrollprize/fiber_selftrain_teacher_epoch30)
   (the same checkpoint also **warm-starts** this model's own weights, i.e.
   this is continued self-training, not distillation from an unrelated
   architecture).
2. An Otsu-adaptive light/dark voxel threshold (`otsu_light_threshold=70`,
   plus `otsu_min_light_voxels`, `otsu_fallback_threshold`,
   `otsu_tail_floor_percentile`, `otsu_min_tail_voxels`).
3. A similarity map between the
   [supcon-fine-tuned DINO backbone, step 362500](https://huggingface.co/scrollprize/dinovol_v2_ps8_supcon3class_step362500)'s
   dense patch embeddings and a single reference "fiber" prototype embedding
   (`avg_fiber_embedding__864d_backbone.npz`, bundled in that backbone's repo),
   computed at stride 128 and blended in with `dino_blend_sigma=4.0`.

We reconstructed this description from the run's own config field names
(`dynamic_label.*`); the specific script implementing this exact blend was not
found in the available `villa` repository snapshot (unlike the 4-class
pipeline discussed below, whose source we did read directly), so treat the
precise algorithmic combination as a well-supported inference, not a verbatim
account of the code.

### Checkpoint provenance: a mid-run bugfix

This run's own config records `resume_from_ckpt` pointing at its own
`ckpt_002000.pth`, under the *same* W&B run ID (`ihoo3tpl`) — confirming
training paused at step 2000 and resumed later in the same run (verified both
via the W&B API and by loading this checkpoint's own embedded config directly,
which lists `wandb_run_id: ihoo3tpl` and the matching `resume_from_ckpt`
path). This lines up exactly with the two checkpoints produced:

- `step_002000__resume_point__pre_dark_mask_fix.pth` — **not published here**
  (superseded).
- `step_010000__post_dark_mask_fix__latest.pth` — **this repo.**

The filenames describe this as a fix to "dark voxel masking." We can confirm
the resume-at-step-2000 mechanics precisely (embedded config + matching
filenames + same run ID) but **cannot independently confirm the exact nature
of the underlying bug/fix** — plausible candidate parameters visible in the
(post-fix) config relate to dark/light voxel handling (`input_mask_threshold`,
`otsu_light_threshold`, the dataset's `dark_threshold`), but we only have the
post-fix config, not a diff against the pre-fix run.

## Metrics

**This run has no held-out validation metric** — its W&B summary contains no
`val_*` key at all, because the entire pipeline is label-free self-training
(there is no independent ground truth to validate against). Final logged
values at step 11999 (of a 12000-step schedule; run marked **finished**):

| metric | value |
|---|---|
| `loss` (bce + dice) | 0.7824 |
| `loss_bce` | 0.3318 |
| `loss_dice` | 0.4506 |
| `pseudo_fg_frac` (dynamic label's foreground fraction) | 0.132 |
| `sim_mean` (mean DINO-embedding similarity to the reference) | 0.432 |
| `otsu_threshold` (final adaptive cut) | 0.503 |
| `lr` | ≈1.1×10⁻¹⁰ (cosine-annealed to ~0) |

These are training-loop / pseudo-label-consistency statistics, not accuracy
against independently verified ground truth.

## Relationship to the 4-class fiber/ink model — please read before assuming this is that model

Villa's actual finished 4-class (background / vertical fiber / horizontal-angular
fiber / ink) self-distillation model — matching
[`scripts/fiber_5class`](https://github.com/ScrollPrize/villa/tree/main/scripts/fiber_5class)
exactly (watershed-from-minima + per-instance PCA orientation split + ink-teacher
override + dark-voxel guard) — is a **separate** checkpoint: W&B run
[`p4_4class_ddp8_20260526`](https://wandb.ai/vesuvius-challenge/paris4-full-features/runs/36pykwky)
(`36pykwky`, project `paris4-full-features`, state finished, created
2026-05-26 — four days after this run). Its config confirms it uses this
checkpoint's lineage as its frozen fiber teacher, plus a separate frozen ink
teacher that we do not have. **We do not currently have that 4-class model's
weight files**: its training `out_dir` was an ephemeral cloud-instance scratch
path (`/ephemeral/fiber_5class_ckpts/p4_4class_ddp8_20260526`), not S3, and a
scoped search of `s3://philodemos/giorgio/PHercParis4/` turned up only
DINO-backbone checkpoints and what appears to be stitched inference *output*
(not model weights). **It is not published on HuggingFace at this time.**

For reference, that run's self-consistency metrics (student vs. its own
pseudo-label on the training crop — again, not held-out validation):
`dice_0_bg`=0.961, `dice_1_vert_fiber`=0.673, `dice_2_horiz_fiber`=0.705,
`dice_3_ink`=0.791, `dice_fg_mean`=0.723.

## Prior / sibling work

An earlier, independently-trained, **supervised** 2-class horizontal/vertical
fiber model (traced from WebKnossos skeleton annotations via cross-frame affine
registration, villa PR [#825](https://github.com/ScrollPrize/villa/pull/825))
is already published as [`scrollprize/fiber_hz_vt`](https://huggingface.co/scrollprize/fiber_hz_vt)
(W&B run `xnjpitfg`, project `fibers`, `val_hzvt_mean_dice`=0.60,
`val_hzvt_mean_iou`=0.52). That model predicts horizontal-vs-vertical
orientation from real annotations; this model predicts fiber-vs-background
from self-generated pseudo-labels. They are not directly comparable.

## Files

| File | Size | Role |
|---|---|---|
| `step_010000__post_dark_mask_fix__latest.pth` | ~2.1 GB | `model` (raw) + `ema.model_state` (recommended for inference) + `optimizer` + embedded `config`. |
| `config.json` | — | The same training config embedded in the checkpoint, for quick inspection without loading the full file. |

## Usage

```python
import torch
from huggingface_hub import hf_hub_download

path = hf_hub_download(
    "scrollprize/fiber_dinoguided_2class_step010000",
    "step_010000__post_dark_mask_fix__latest.pth",
)
ckpt = torch.load(path, map_location="cpu", weights_only=False)
state = ckpt["ema"]["model_state"]   # recommended over ckpt["model"]
# Build with vesuvius' NetworkFromConfig (target "fibers", out_channels=2,
# in_channels=1, patch_size 256^3) then load_state_dict(state).
```
The `vesuvius` package is in <https://github.com/ScrollPrize/villa>.

## Related models

- **Frozen fiber teacher / weight init for this run:** [`scrollprize/fiber_selftrain_teacher_epoch30`](https://huggingface.co/scrollprize/fiber_selftrain_teacher_epoch30)
- **Frozen DINO backbone used for guidance:** [`scrollprize/dinovol_v2_ps8_supcon3class_step362500`](https://huggingface.co/scrollprize/dinovol_v2_ps8_supcon3class_step362500)
- **Prior supervised hz/vt model:** [`scrollprize/fiber_hz_vt`](https://huggingface.co/scrollprize/fiber_hz_vt)

## Links

- **Code:** <https://github.com/ScrollPrize/villa> — PR [#825](https://github.com/ScrollPrize/villa/pull/825) (cross-frame affine infra), PR [#985](https://github.com/ScrollPrize/villa/pull/985) (`scripts/fiber_5class`, the downstream 4-class trainer that consumes this checkpoint)
- **W&B run:** <https://wandb.ai/vesuvius-challenge/vesuvius_fibers_3d/runs/ihoo3tpl>
- **Data:** <https://scrollprize.org/data_browser>
- **Vesuvius Challenge:** <https://scrollprize.org>

## License

MIT.