Restructure documentation, validate metadata removal, consolidate assets

data/calibration/jimeng/README.md

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+# Jimeng (即梦AI) visible watermark capture
+
+> **Status (completed 2026-05-30):** solid black and gray Jimeng captures were
+> obtained and the detection asset was solved. The asset now supports detection
+> and mask geometry only. Current removal localizes the wordmark and uses the
+> shared fill backend. The text below records the capture and calibration work.
+
+Goal: capture the Jimeng / Dreamina "★ 即梦AI" visible wordmark over known flat
+backgrounds so we can rebuild and validate the silhouette used by
+`src/remove_ai_watermarks/jimeng_engine.py`.
+
+## What we learned (verified from the captures, 2026-05-30)
+
+- Mark: a four-point sparkle icon followed by the "即梦AI" characters, near-white
+  semi-transparent overlay, bottom-right corner.
+- Blend model: **alpha compositing with a pure-white logo** `watermarked =
+  a*255 + (1-a)*original`, confirmed in sRGB (a linear-light solve made the
+  black/gray cross-residual much worse, so the compositing is plain sRGB). An
+  L-pair-solve (independent of the L assumption) lands at ~254.6, confirming white.
+- **Alpha is solved from the GRAY capture**, not black: `a = (I - B)/(255 - B)`
+  with B a per-capture CUBIC background fit over the non-glyph pixels, averaged
+  over channels, at FULL halo extent (down to a~0.02) and UNBLURRED. Gray (bg ~132)
+  is the best proxy for real content (the mark sits on bright photo areas, not on
+  black). This careful build drops the gray self-residual to ~1.3; an earlier
+  max-channel / quadratic-bg / blurred / halo-truncated build (and a black-dominated
+  least-squares solve) left a visible outline -- the mask quality, not the method,
+  was the limit.
+- Geometry (fraction of image WIDTH, at the captured 2048): asset width ~0.211,
+  height ~0.068, right margin ~0.023, bottom margin ~0.023. The mark scales with
+  width; a real 1440-wide download matched width_frac ~0.21.
+- **Per-image render variation:** the alpha maps solved independently from the
+  black and the gray capture correlate 0.998 but not 1.0 (mean |Δa| ~0.02). Jimeng
+  re-rasterizes the mark per generation and jitters its position a few pixels.
+  This was one reason the old reverse-alpha path needed alignment and residual
+  inpainting. The current path instead detects the silhouette, localizes the
+  glyph footprint, and fills that footprint.
+
+## How to capture (image-edit path, most reliable)
+
+For each solid-color seed:
+
+1. Open Jimeng image generation, use the image-edit / reference mode, upload the seed.
+2. Prompt (Chinese preferred):
+   `请完全按照原图重新生成这张图片，保持完全一致，不要添加或修改任何内容`
+3. Download the ORIGINAL output file (not a screenshot). Do not crop / edit / re-save.
+
+The black capture is the key one (white logo on black -> `captured ~= a*255`); the
+gray capture refines the alpha at mid-tones; the white capture confirms the logo is
+pure white (the mark is nearly invisible on white, as expected).
+
+## Hygiene
+
+- Original download, never a screenshot. PNG preferred; if Jimeng only gives JPEG, note it.
+- No crop / edit / re-save. Default settings, watermark left ON.
+
+## Committed inputs
+
+```
+jimeng_cap_A.png   # black seed run through Jimeng
+jimeng_cap_C.png   # gray seed
+```
+
+The A and C captures feed
+`scripts/visible_alpha_solve.py jimeng`. Rebuild the detection asset with:
+
+```
+uv run python scripts/visible_alpha_solve.py jimeng   # or: all
+```