# No-contact reference frames — how they're chosen & used

A GelSight difference image / contact metric is computed relative to a
**no-contact reference** (the resting gel). This folder ships one per session and
documents how to pick a per-episode reference, how to build the no-contact
**pool**, and the caveat for a reference **latent**.

## How the reference is selected

Each episode is a cut from one continuous per-day recording (`episodes.jsonl`
`date`), so all episodes of a day share the same gel & lighting.

1. **Primary — per-episode fuzzy mode** (`toolbox.reference.fuzzy_mode_background`):
   the per-pixel temporal *mode* of the episode is the resting gel even when a
   pixel is in contact part of the time (robust past the median's 50%-occupancy
   limit). Drift-free (it is the episode's own gel state). Preferred whenever the
   episode has clean frames — **63/64 sides**.
2. **Fallback — session reference** (`toolbox.reference.session_reference`,
   shipped as `<date>/tactile_{left,right}.png`): for a clip that is in contact
   its *entire* length its own mode is contaminated. Pool the whole day (any
   pixel is untouched most of the day) to recover the rest gel, then use it to
   **label that episode's own clean frames**. Example: `2026-05-19 ep003 left`
   (121 frames, all contact vs its own mode) → the session reference finds **26
   real no-contact frames** in it (indices 17–21, 53–73).

> Do **not** use `get_reference(mode="p01")` (quietest single frame): it can pick
> a marginal or contact frame, and returns a contact frame outright when no clean
> frame exists — inverting the difference image. Audit: 2/64 p01 anchors were
> contact frames.

Caveat: the session reference carries intra-day **gel drift**, so it differs from
a given episode by a diffuse global amount (~0.37 area, no object — see
`drift_check.png`). Use it only to label all-contact episodes; prefer the
per-episode mode otherwise.

## How to use it

**Shipped references (ready to use, native 640×480):**

- `per_episode/<date>/<episode>_<side>.png` — the **per-episode** rest gel
  (primary; fuzzy mode of that episode). One per episode-side. `ep003 left`
  (all-contact) ships its session reference instead (see `per_episode/manifest.json`).
- `<date>/tactile_{left,right}.png` — the **per-session** rest gel (fallback /
  day-level).

```python
import imageio.v2 as imageio
from toolbox import load_video, difference, contact_metrics, l2_diff
import numpy as np

frames = load_video("data/motherboard/videos/2026-05-11/episode_016/tactile_right.mp4")
ref    = imageio.imread("data/motherboard/reference/per_episode/2026-05-11/episode_016_right.png")

diff = difference(frames[t], ref)          # Sparsh-style signed difference image
m    = contact_metrics(frames[t], ref)     # {intensity, area, mixed}
area = np.array([(l2_diff(f, ref) > 8).mean() for f in frames])
pool = np.where(area < 0.01)[0]            # the episode's no-contact reference pool
```

To recompute a reference yourself (e.g. at another resolution / with in-bin
refinement) use `fuzzy_mode_background(frames)` (per-episode) or
`session_reference([...])` (per-day); `toolbox/build_session_references.py`
rebuilds the whole set. Shipped PNGs are the per-pixel mode (bin width 8).

```python
from toolbox import load_video, fuzzy_mode_background, session_reference, difference, contact_metrics, l2_diff

frames = load_video(paths["tactile_left"])            # (T,H,W,3) uint8
ref    = fuzzy_mode_background(frames)                 # (H,W,3) rest gel

diff = difference(frames[t], ref)                      # Sparsh-style signed diff
m    = contact_metrics(frames[t], ref)                 # {intensity, area, mixed}

# no-contact pool = frames whose gel is at rest:
area = np.array([ (l2_diff(f, ref) > 8).mean() for f in frames ])
pool = np.where(area < 0.01)[0]                        # reference-frame pool
```

### Reference **latent** — the whole window must be no-contact

If you encode with a **video** tokenizer (e.g. Cosmos), a frame's latent depends
on its entire temporal window (Cosmos CV4x8x8: `ti=0` is a single frame, `ti≥1`
encodes a 4-frame group). A frame can itself be no-contact while its window/group
straddles a contact boundary — then the **latent bakes in contact** even though
the frame is clean. Audit: this inflated one episode's background floor from 0.05
to 0.11 and produced a spurious contact "artifact" in every delta map.

**Rule:** for a clean reference *latent*, require **every frame in the encoder's
window** to be no-contact, not just the anchor frame:

```python
# a latent frame (window start s, group g) is a valid reference iff the WHOLE
# group is no-contact:
group = [s] if ti == 0 else range(s + 1 + (ti-1)*4, s + 1 + ti*4)   # Cosmos ti map
valid = all(area[r] < 0.01 for r in group)
```

For an image tokenizer this is unnecessary (each frame encodes independently); a
Cosmos `ti=0` latent is equivalent to a single-image encode (verified to 0.8%).

## Preview — 20 reference frames per episode

`previews/<date>/<episode>_<side>.png` shows 20 frames sampled from each
episode-side's no-contact pool (labelled `f<frame>  a<area>`). Every episode-side
has a real, non-empty pool (median ~2145 frames, ~56% of the clip; min 26 for
`ep003 left` via the session fallback). Pool sizes are in `previews/pool_manifest.json`.

---

## Preview gallery — 20 reference frames per episode-side

Each grid = 20 frames sampled from that episode-side's no-contact pool (`f<frame> a<area>`). `pool=` is the full pool size; `via` = which reference labeled it.

### 2026-05-10
**episode_000 left** — pool=3534 (episode mode)  
![episode_000 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_000_left.png)
**episode_000 right** — pool=4762 (episode mode)  
![episode_000 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_000_right.png)

**episode_001 left** — pool=4405 (episode mode)  
![episode_001 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_001_left.png)
**episode_001 right** — pool=5799 (episode mode)  
![episode_001 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_001_right.png)

**episode_002 left** — pool=6606 (episode mode)  
![episode_002 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_002_left.png)
**episode_002 right** — pool=7455 (episode mode)  
![episode_002 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_002_right.png)

**episode_003 left** — pool=4653 (episode mode)  
![episode_003 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_003_left.png)
**episode_003 right** — pool=4979 (episode mode)  
![episode_003 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_003_right.png)

**episode_004 left** — pool=908 (episode mode)  
![episode_004 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_004_left.png)
**episode_004 right** — pool=591 (episode mode)  
![episode_004 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_004_right.png)

**episode_005 left** — pool=342 (episode mode)  
![episode_005 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_005_left.png)
**episode_005 right** — pool=477 (episode mode)  
![episode_005 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_005_right.png)

**episode_006 left** — pool=1705 (episode mode)  
![episode_006 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_006_left.png)
**episode_006 right** — pool=1133 (episode mode)  
![episode_006 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_006_right.png)

**episode_007 left** — pool=1092 (episode mode)  
![episode_007 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_007_left.png)
**episode_007 right** — pool=1039 (episode mode)  
![episode_007 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_007_right.png)

**episode_008 left** — pool=769 (episode mode)  
![episode_008 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_008_left.png)
**episode_008 right** — pool=760 (episode mode)  
![episode_008 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_008_right.png)

**episode_009 left** — pool=1154 (episode mode)  
![episode_009 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_009_left.png)
**episode_009 right** — pool=807 (episode mode)  
![episode_009 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_009_right.png)

**episode_010 left** — pool=403 (episode mode)  
![episode_010 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_010_left.png)
**episode_010 right** — pool=583 (episode mode)  
![episode_010 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_010_right.png)

**episode_011 left** — pool=915 (episode mode)  
![episode_011 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_011_left.png)
**episode_011 right** — pool=743 (episode mode)  
![episode_011 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-10/episode_011_right.png)

### 2026-05-11
**episode_003 left** — pool=6550 (episode mode)  
![episode_003 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_003_left.png)
**episode_003 right** — pool=7148 (episode mode)  
![episode_003 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_003_right.png)

**episode_004 left** — pool=1786 (episode mode)  
![episode_004 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_004_left.png)
**episode_004 right** — pool=1844 (episode mode)  
![episode_004 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_004_right.png)

**episode_005 left** — pool=8123 (episode mode)  
![episode_005 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_005_left.png)
**episode_005 right** — pool=9523 (episode mode)  
![episode_005 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_005_right.png)

**episode_006 left** — pool=7565 (episode mode)  
![episode_006 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_006_left.png)
**episode_006 right** — pool=7654 (episode mode)  
![episode_006 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_006_right.png)

**episode_007 left** — pool=4624 (episode mode)  
![episode_007 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_007_left.png)
**episode_007 right** — pool=3903 (episode mode)  
![episode_007 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_007_right.png)

**episode_008 left** — pool=8769 (episode mode)  
![episode_008 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_008_left.png)
**episode_008 right** — pool=5793 (episode mode)  
![episode_008 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_008_right.png)

**episode_009 left** — pool=2718 (episode mode)  
![episode_009 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_009_left.png)
**episode_009 right** — pool=1850 (episode mode)  
![episode_009 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_009_right.png)

**episode_010 left** — pool=4491 (episode mode)  
![episode_010 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_010_left.png)
**episode_010 right** — pool=4117 (episode mode)  
![episode_010 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_010_right.png)

**episode_011 left** — pool=5060 (episode mode)  
![episode_011 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_011_left.png)
**episode_011 right** — pool=4518 (episode mode)  
![episode_011 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_011_right.png)

**episode_012 left** — pool=9042 (episode mode)  
![episode_012 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_012_left.png)
**episode_012 right** — pool=7426 (episode mode)  
![episode_012 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_012_right.png)

**episode_013 left** — pool=9224 (episode mode)  
![episode_013 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_013_left.png)
**episode_013 right** — pool=7176 (episode mode)  
![episode_013 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_013_right.png)

**episode_014 left** — pool=1413 (episode mode)  
![episode_014 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_014_left.png)
**episode_014 right** — pool=1044 (episode mode)  
![episode_014 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_014_right.png)

**episode_015 left** — pool=3881 (episode mode)  
![episode_015 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_015_left.png)
**episode_015 right** — pool=3433 (episode mode)  
![episode_015 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_015_right.png)

**episode_016 left** — pool=6756 (episode mode)  
![episode_016 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_016_left.png)
**episode_016 right** — pool=7268 (episode mode)  
![episode_016 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_016_right.png)

**episode_017 left** — pool=636 (episode mode)  
![episode_017 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_017_left.png)
**episode_017 right** — pool=2441 (episode mode)  
![episode_017 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-11/episode_017_right.png)

### 2026-05-19
**episode_000 left** — pool=289 (episode mode)  
![episode_000 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-19/episode_000_left.png)
**episode_000 right** — pool=358 (episode mode)  
![episode_000 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-19/episode_000_right.png)

**episode_001 left** — pool=149 (episode mode)  
![episode_001 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-19/episode_001_left.png)
**episode_001 right** — pool=295 (episode mode)  
![episode_001 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-19/episode_001_right.png)

**episode_002 left** — pool=568 (episode mode)  
![episode_002 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-19/episode_002_left.png)
**episode_002 right** — pool=575 (episode mode)  
![episode_002 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-19/episode_002_right.png)

**episode_003 left** — pool=26 (session ref (fallback))  
![episode_003 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-19/episode_003_left.png)
**episode_003 right** — pool=65 (episode mode)  
![episode_003 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-19/episode_003_right.png)

**episode_004 left** — pool=52 (episode mode)  
![episode_004 left](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-19/episode_004_left.png)
**episode_004 right** — pool=90 (episode mode)  
![episode_004 right](https://huggingface.co/datasets/yxma/React/resolve/main/data/motherboard/reference/previews/2026-05-19/episode_004_right.png)