The reverse-alpha text-mark engine (Doubao/Jimeng/Samsung) allocated
full-frame arrays where only the glyph footprint is ever read:
- _fixed_alpha_map / _aligned_alpha_map each built a full (h, w) float32
alpha map non-zero only inside the glyph box, and two were held at once
during removal (~96 MB of mostly-zeros on a 12 MP frame);
- extract_mask built a full (h, w) uint8 mask that every caller cropped to
the located box (~12 MB, rebuilt per text-mark detector on the
memory-tight identify path).
Both now return footprint-sized arrays: the alpha helpers return the
glyph-sized block plus its placement (ax, ay, gw, gh), and extract_mask
returns the box-sized mask. _apply_reverse_alpha consumes the block
directly; the residual inpaint embeds it into one full-frame uint8 mask only
at cv2.inpaint time (which needs a full-frame mask). remove_watermark_
reverse_alpha tracks the winning region alongside best_amap to place it.
Peak allocation drops from O(image*4)x2 + O(image) to O(footprint)x2 +
one gated O(image*1) uint8 mask -- a win every consumer gets, motivated by
the 512 MB raiw.cc worker that OOMs on large decodes. GPU path untouched.
Byte-identical to the old full-frame path (verified: 17 output hashes
across the three engines, inpaint/no-inpaint, detect, and the real
doubao-1.png fixture, unchanged before/after). tests/test_text_mark_memory.py
guards it by reconstructing the old full-frame path inline and asserting
equality, so the proof survives a cv2/asset bump, and pins the O(footprint)
shape so a regression to full-frame fails loudly.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
The free `visible` path over-subtracted a faint Gemini sparkle on a
mid-tone background into a darker-than-background brown diamond instead
of removing it (2026-06-18 prod NPS report, "the watermark was not
removed, just its color changed"). The existing over-subtraction guard
only tripped when reverse-alpha drove a footprint pixel fully negative
(the issue #30 dark-background black-pit case); on a mid-tone background
the over-subtraction darkens the core well below the background without
any pixel crossing zero, so the gate missed it and shipped the dark mark.
Add a second over-subtraction signal to `_reverse_alpha_oversubtracts`:
predict the reverse-alpha output at the bright core, (core - a*logo)/(1-a),
and route to the footprint inpaint when it lands more than
`_OVERSUB_DARK_MARGIN` (25) gray levels below the local background ring.
Calibrated wide: clean removals predict within ~12 of background
(demo_banana ~-1), the prod regression ~-40, the issue #30 dark case ~-82.
Corpus-validated on the 479 detected Gemini images: 10 switch reverse-alpha
to inpaint, all of them dark-diamond cases that improve or match; the
other 469 stay byte-identical. demo_banana stays on the reverse-alpha
path (byte-identical).
Also crop both reverse-alpha helpers to the region they actually touch,
a pure O(image) -> O(mark) win that is byte-identical to the full-frame
math (a uint8<->float32 round-trip is exact):
- `GeminiEngine._core_and_bg` converts only the footprint+ring crop to
gray, not the whole frame (~70 ms -> 0.1 ms on a 12 MP image; it runs
for both the alpha-gain estimate and the new gate). Verified identical
across 479 images; detector confidence unchanged.
- `TextMarkEngine._apply_reverse_alpha` computes the blend on the glyph
crop only (`amap` is zero outside it, so the math is a no-op there):
~275 ms -> ~2 ms per placement on a 12 MP frame, up to 2 placements per
removal. Verified identical across 142 Doubao/Jimeng placements.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
The 256->512 detection-search widening (v0.8) let a large, low-gradient
shape match outrank a genuine mid-size corner sparkle whose raw NCC sits
below the 0.85 corner-promote gate, so `identify` read `unknown` on Gemini
images that v0.7.2 caught (reporter osachub: scale-48 sparkle on light
bedding -- true sparkle spatial 0.775 / grad 0.960 / fusion 0.676, but the
size-weighted argmax locked onto a decoy at spatial 0.628 / grad 0.036).
detect_watermark now keeps the top-K (_SELECT_TOPK=3) size-weighted
candidates (NMS-deduped) plus the corner-promote candidate, scores each by
full fusion (spatial+gradient+variance) via the extracted _grad_var_scores
helper, and selects the highest -- the gradient term lifts the true sparkle
over the decoy. Ranking by the SIZE-WEIGHTED score (not a raw-NCC argmax)
preserves tiny-patch suppression: a raw-NCC argmax re-admitted 16-18px
content false positives (14/65 doubao + 4/11 jimeng visible images). Top-K
adds zero flips on the doubao/jimeng corpora and leaves the 495-image Gemini
set unchanged (479 detected) while recovering the reporter's image at 0.676.
- _grad_var_scores: gradient/variance scoring factored out of detect_watermark
- confidence = best_fused (drop the duplicated fusion recompute)
- tests: rename test_promotion_is_what_rescues_it ->
test_size_weighted_search_alone_traps_on_the_decoy (corner-promote is no
longer the sole rescue path); add a deterministic regression test mirroring
the real spatial/grad signature
- docs: module-internals.md detector section + CLAUDE.md mechanism map
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Victor Kuznetsov