| """Reference (background) frame handling + difference image for GelSight. |
| |
| GelSight Mini is markerless, so background subtraction is clean (no markers |
| to occlude). Convention follows Sparsh (Meta, CoRL 2024): a single no-contact |
| reference frame + signed per-channel difference. |
| |
| All frames are RGB uint8 (H, W, 3) — the convention returned by the dataset's |
| video decoder. |
| """ |
| from __future__ import annotations |
|
|
| import numpy as np |
|
|
|
|
| def get_reference(frames, mode: str = "p01", intensity=None, window: int = 30): |
| """Pick a no-contact reference frame from a sequence. |
| |
| frames: (T, H, W, 3) uint8 OR a callable i->frame for lazy access with |
| an explicit `intensity` array. |
| mode: |
| "first" -> frames[0] |
| "p01" -> the 1st-percentile-intensity (quietest) frame; needs |
| `intensity` (T,) array of per-frame contact intensity, |
| else computes a cheap proxy = mean abs deviation from |
| the temporal median. |
| "running_avg" -> mean of the `window` lowest-intensity frames. |
| Returns an (H, W, 3) uint8 reference. |
| """ |
| arr = np.asarray(frames) |
| T = arr.shape[0] |
| if mode == "first": |
| return arr[0].copy() |
|
|
| if intensity is None: |
| med = np.median(arr.reshape(T, -1).astype(np.float32), axis=0) |
| intensity = np.abs(arr.reshape(T, -1).astype(np.float32) - med).mean(axis=1) |
| intensity = np.asarray(intensity, np.float32) |
|
|
| if mode == "p01": |
| thr = np.percentile(intensity, 1) |
| idx = int(np.where(intensity <= thr)[0][0]) if (intensity <= thr).any() else int(intensity.argmin()) |
| return arr[idx].copy() |
|
|
| if mode == "running_avg": |
| k = min(window, T) |
| order = np.argsort(intensity)[:k] |
| return arr[order].mean(axis=0).round().astype(np.uint8) |
|
|
| raise ValueError(f"unknown reference mode: {mode}") |
|
|
|
|
| def difference(frame, reference, signed: bool = True): |
| """Sparsh-style difference image. |
| |
| signed=True -> (frame - ref)/255 + 0.5, clipped to [0,1], scaled to uint8. |
| Mid-gray = no change; preserves direction of deformation. |
| signed=False -> |frame - ref| as uint8 (magnitude only). |
| |
| frame/reference: (H, W, 3) uint8. Returns (H, W, 3) uint8. |
| """ |
| f = frame.astype(np.float32) |
| r = reference.astype(np.float32) |
| if signed: |
| d = (f - r) / 255.0 + 0.5 |
| return (np.clip(d, 0, 1) * 255).astype(np.uint8) |
| return np.clip(np.abs(f - r), 0, 255).astype(np.uint8) |
|
|
|
|
| def l2_diff(frame, reference): |
| """Per-pixel L2 distance across RGB channels (H, W) float32. |
| |
| This is the quantity the dataset's contact scalars are built on: |
| d[h,w] = ||frame[h,w,:] - ref[h,w,:]||_2. |
| """ |
| return np.sqrt(((frame.astype(np.float32) - reference.astype(np.float32)) ** 2).sum(axis=2)) |
|
|
