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:

Open Jimeng image generation, use the image-edit / reference mode, upload the seed.
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
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