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dyn-object-masks

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Generate dynamic-object binary masks after global motion compensation, output CSR sparse format.

tasks/dynamic-object-aware-egomotion/environment/skills/dyn-object-masks/SKILL.md

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Nov 4, 2026
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# When to use
- Detect moving objects in scenes with camera motion; produce sparse masks aligned to sampled frames.

# Workflow
1) **Global alignment**: warp previous gray frame to current using estimated affine/homography.
2) **Valid region**: also warp an all-ones mask to get `valid` pixels, avoiding border fill.
3) **Difference + adaptive threshold**: `diff = abs(curr - warp_prev)`; on `diff[valid]` compute median + 3×MAD; use a reasonable minimum threshold to avoid triggering on noise.
4) **Morphology + area filter**: open then close; keep connected components above a minimum area (tune as fraction of image area or a fixed pixel threshold).
5) **CSR encoding**: for final bool mask  
   - `rows, cols = nonzero(mask)`  
   - `indices = cols.astype(int32)`; `data = ones(nnz, uint8)`  
   - `counts = bincount(rows, minlength=H)`; `indptr = cumsum(counts, prepend=0)`  
   - store as `f_{i}_data/indices/indptr`
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