Mask faint text marks with the detector's match box, not a response threshold

The faint-mask fallback added for the tophat front-end thresholded the
max-normalized uint8 response at 0.5 -- which selects every non-zero pixel,
not "half the peak" as its comment claimed -- and filled ~120% of the corner
box on textured frames. Measured on 14 real faint-path frames (cv2 fill,
detector re-run after): the detector's own best-match box fills a 58.7%-median
corner box vs 120.9% for the threshold, both 100% detector-clean. Detection and
the mask now read one method, _tophat_best, whose score gates detection and
whose argmax box bounds the fill, so the two cannot drift by construction --
which is how the mismatch arose. The 0.5 constant is deleted.

Parity could not catch this (a mask that fills everything is trivially
detector-clean) and the regression test could not either: its flat fixture
gives every threshold the same box, so mutating the constant to 99.0 stayed
green. The fixture now carries texture and asserts the mask area is bounded,
not merely non-empty; it reproduces the corpus number (127% pre-fix).

Also lands the Tier B2 verification harnesses that found and bounded this:
- detector_response.py: response curves (detected AND maskable per cell); found
  the size response is a comb, contrast is near-irrelevant, no unmaskable cells.
- ladder_headroom.py: measured that a denser scale ladder recovers 7.6% of
  misses for a 2.52%->3.05% false-fire rise, and the one landscape rung that
  helps is a geometry shift that helps and hurts equally (1.7:1) -- do not add.
- cjk_tail_probe.py: a generic shared-tail (AI生成) template does not separate
  uncovered vendors from clean corners (0.407 vs clean p99 0.298).

Records the visible-parity re-run confirming the earlier front-end fix (doubao
91.8% -> 99.3%), and dedups the thrice-written stamp forward model into one
fill_quality.composite.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Victor Kuznetsov
2026-07-20 15:41:18 -07:00
co-authored by Claude Opus 4.8
parent 7d00debdca
commit 52eb40c2ca
10 changed files with 1213 additions and 70 deletions
+272
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"""Can one GENERIC template cover the CJK AI labels no per-vendor detector fires on?
THE OPPORTUNITY
Corpus inspection of doubao-provenance misses turned up `千问AI生成` (Alibaba Qwen) and
`百度 AI生成` (Baidu) sitting in the same bottom-right corner as the marks we do cover,
bold and plainly legible, with no detector able to fire on either. `docs/...landscape`
puts uncovered vendors at ~6% of sampled images -- larger than any tuning gain left in
the covered ones (a dense scale ladder recovers 1 miss in 26; see ladder_headroom.py).
WHY A SHARED TEMPLATE IS EVEN PLAUSIBLE
China's GB 45438-2025 mandates the label, and every compliant vendor ends it with the
same run: `AI生成`. The vendor PREFIX varies (豆包 / 千问 / 百度 / 星绘) and is what makes
per-vendor silhouettes expensive; the TAIL is guaranteed. So the tail is the part worth
detecting, and vendor attribution -- which the shared tail cannot provide anyway
(measured 千问-vs-doubao AUC ~0.5) -- moves to metadata, where it is reliable.
WHY IT IS WORTH RETRYING NOW
`render_vendor_silhouettes.py` records 千问 as ruled out, and its reasoning was sound:
the then-current front-end binarized the glyph, and a thin translucent overlay shatters
into specks that no template can match. It closes by naming what would be needed --
"a detection front-end that does not depend on binarizing the glyph (grayscale/edge
correlation on the raw top-hat)". That front-end now EXISTS: `detect_frontend="tophat"`
was built for doubao and correlates a soft template against the continuous response.
The blocker was removed by unrelated work, so the ruling deserves re-measurement rather
than inheritance.
THE MEASUREMENT
Three arms, one scorer (the tail template on the tophat response, swept over a dense
size ladder because an unregistered vendor's glyph size is genuinely unknown -- the one
place a dense ladder earns its cost):
covered a registered mark already fires -- a sanity arm; the tail is inside those
marks too, so a tail template that cannot score THESE is simply broken
uncovered TC260 provenance but no detector fires -- the target population
clean no metadata signal at all -- the precision arm
The decision rests on whether `uncovered` carries a high-scoring subpopulation that
`clean` does not. It does NOT rest on the raw rate: TC260 provenance does not imply a
visible mark, so a modest fire rate on that arm is expected even if the detector is
perfect. Any threshold this suggests must then be confirmed by eyeballing the crops it
selects -- the script writes a contact sheet for exactly that.
DATA SAFETY
Corpus images are user uploads: read-only, local analysis, gitignored output. The
template is font-rendered synthetic, never cut from a user upload.
uv run python scripts/cjk_tail_probe.py --n 6000
"""
from __future__ import annotations
import argparse
import glob
import json
import os
import random
import sys
from concurrent.futures import ProcessPoolExecutor, as_completed
from pathlib import Path
from typing import Any
import cv2
import numpy as np
sys.path.insert(0, str(Path(__file__).parent.parent))
sys.path.insert(0, str(Path(__file__).parent))
REPO = Path(__file__).resolve().parents[1]
CORPUS = REPO / "data" / "spaces" / "originals"
OUT = REPO / "data" / "spaces" / "_cjk_tail_probe.jsonl"
# Cached under the gitignored data dir, not in scripts/: this is a probe artifact, not a
# product asset. If the tail mark is ever registered, `render_vendor_silhouettes.py` is
# what writes the committed silhouette into src/.../assets/.
TAIL_PNG = REPO / "data" / "spaces" / "_cjk_tail_silhouette.png"
# The tail is a fraction of a full vendor mark's width (`豆包AI生成` is ~5 CJK widths,
# `AI生成` ~3), and the prefix length differs per vendor, so the size is genuinely
# unknown here -- unlike a registered mark, whose fraction is calibrated. Hence a wide,
# dense ladder: this is the case a dense ladder is actually for.
TAIL_SCALES = tuple(round(0.30 * (1.08**i), 4) for i in range(18)) # ~0.30 .. ~1.15
def build_tail_silhouette() -> np.ndarray:
"""Font-rendered `AI生成` silhouette, cached next to this script (data-safe)."""
if TAIL_PNG.exists():
img = cv2.imread(str(TAIL_PNG), cv2.IMREAD_GRAYSCALE)
if img is not None:
return img
from render_vendor_silhouettes import render
sil = render("AI生成", width=200)
cv2.imwrite(str(TAIL_PNG), sil)
return sil
def tail_score(engine: Any, image: np.ndarray, sil: np.ndarray) -> tuple[float, float]:
"""Best tail correlation over the size ladder; returns (score, winning_scale)."""
loc = engine.locate(image)
resp = engine.tophat_response(image, loc)
if resp is None:
return (0.0, 0.0)
c = engine.config
base = engine.scale_base(image)
ar = sil.shape[0] / max(1, sil.shape[1])
best, best_s = 0.0, 0.0
for s in TAIL_SCALES:
gw = max(12, int(c.alpha_width_frac * base * s))
gh = max(6, int(gw * ar))
if gw >= resp.shape[1] or gh >= resp.shape[0]:
continue
t = cv2.resize(sil, (gw, gh), interpolation=cv2.INTER_AREA)
v = float(cv2.matchTemplate(resp, t, cv2.TM_CCOEFF_NORMED).max())
if v > best:
best, best_s = v, s
return (best, best_s)
def _one(path_str: str) -> dict[str, Any] | None:
from remove_ai_watermarks.api import visible_provenance
from remove_ai_watermarks.doubao_engine import DoubaoEngine
from remove_ai_watermarks.identify import identify
from remove_ai_watermarks.image_io import imread
from remove_ai_watermarks.watermark_registry import detect_marks
path = Path(path_str)
try:
prov = visible_provenance(path)
except Exception:
return None
tc260 = bool({"doubao", "jimeng"} & prov)
if not tc260:
try:
if identify(path, check_visible=False).signals:
return None # some other provenance: neither target nor clean control
except Exception:
return None
img = imread(path_str)
if img is None or min(img.shape[:2]) < 200:
return None
try:
fired = [d.key for d in detect_marks(img) if d.detected]
except Exception:
return None
if fired:
arm = "covered"
elif tc260:
arm = "uncovered"
else:
arm = "clean"
score, scale = tail_score(DoubaoEngine(), img, build_tail_silhouette())
return {
"src": path.name,
"arm": arm,
"fired": fired,
"tail_score": round(score, 4),
"tail_scale": scale,
}
def main() -> None:
ap = argparse.ArgumentParser()
ap.add_argument("--n", type=int, default=6000)
ap.add_argument("--workers", type=int, default=max(1, (os.cpu_count() or 4) - 2))
ap.add_argument("--out", type=Path, default=OUT)
ap.add_argument("--report-only", action="store_true")
ap.add_argument(
"--sheet-at", type=float, default=0.0, help="write a contact sheet of `uncovered` crops scoring >= this"
)
a = ap.parse_args()
if a.report_only:
rows = [json.loads(x) for x in a.out.read_text(encoding="utf-8").splitlines() if x.strip()]
report(rows)
if a.sheet_at:
contact_sheet(rows, a.sheet_at)
return
build_tail_silhouette()
pool = glob.glob(str(CORPUS / "*" / "*"))
random.Random(19).shuffle(pool) # noqa: S311 -- deterministic sampling, not crypto
pool = pool[: a.n]
print(f"scanning {len(pool)} corpus files workers={a.workers}")
print(f"tail ladder {TAIL_SCALES[0]} .. {TAIL_SCALES[-1]} ({len(TAIL_SCALES)} rungs)\n", flush=True)
rows: list[dict[str, Any]] = []
a.out.parent.mkdir(parents=True, exist_ok=True)
with open(a.out, "w", encoding="utf-8") as fh, ProcessPoolExecutor(max_workers=a.workers) as ex:
futures = [ex.submit(_one, p) for p in pool]
for i, fut in enumerate(as_completed(futures), 1):
try:
rec = fut.result()
except Exception: # noqa: S112 -- one bad file must not kill the sweep
continue
if rec is None:
continue
fh.write(json.dumps(rec) + "\n")
rows.append(rec)
if i % 500 == 0:
fh.flush()
print(f" {i}/{len(pool)} usable={len(rows)}", flush=True)
report(rows)
if a.sheet_at:
contact_sheet(rows, a.sheet_at)
def report(rows: list[dict[str, Any]]) -> None:
arms = {k: [r for r in rows if r["arm"] == k] for k in ("covered", "uncovered", "clean")}
print(f"\n{'=' * 80}\nGENERIC CJK TAIL PROBE ({', '.join(f'{k}={len(v)}' for k, v in arms.items())})\n{'=' * 80}")
print("\nScore distribution of the shared `AI生成` tail on the tophat response\n")
print(f"{'arm':11s} {'n':>6s} {'p50':>7s} {'p75':>7s} {'p90':>7s} {'p95':>7s} {'p99':>7s} {'max':>7s}")
for k, v in arms.items():
if not v:
continue
s = np.array([r["tail_score"] for r in v])
qs = [np.percentile(s, q) for q in (50, 75, 90, 95, 99)]
print(f"{k:11s} {len(v):6d} " + " ".join(f"{q:7.3f}" for q in qs) + f" {s.max():7.3f}")
if arms["clean"] and arms["uncovered"]:
clean = np.array([r["tail_score"] for r in arms["clean"]])
unc = np.array([r["tail_score"] for r in arms["uncovered"]])
print("\n\nOPERATING POINTS -- threshold set on the CLEAN arm, yield read on `uncovered`")
print("`clean` fires are the cost; `uncovered` fires are candidate recoveries that")
print("still need eyeballing, since TC260 provenance does not imply a visible mark.\n")
print(f"{'threshold':>10s} {'clean fire':>12s} {'uncovered fire':>16s} {'candidates':>12s}")
for q in (95, 97.5, 99, 99.5, 99.9):
t = float(np.percentile(clean, q))
cf = float((clean >= t).mean())
uf = float((unc >= t).mean())
print(f"{t:10.3f} {100 * cf:11.2f}% {100 * uf:15.1f}% {int((unc >= t).sum()):12d}")
cov = arms["covered"]
if cov:
s = np.array([r["tail_score"] for r in cov])
print(f"\n\nSANITY: on frames where a registered mark fires, the tail scores median {np.median(s):.3f}.")
print("A tail template that cannot score these is broken, whatever it does elsewhere.")
def contact_sheet(rows: list[dict[str, Any]], thresh: float, limit: int = 30) -> None:
"""Crop the corner of the top-scoring `uncovered` frames so the fires can be judged."""
from remove_ai_watermarks.doubao_engine import DoubaoEngine
from remove_ai_watermarks.image_io import imread
eng = DoubaoEngine()
picks = sorted(
(r for r in rows if r["arm"] == "uncovered" and r["tail_score"] >= thresh),
key=lambda r: -r["tail_score"],
)[:limit]
tiles = []
for r in picks:
hits = glob.glob(str(CORPUS / "*" / r["src"]))
if not hits:
continue
img = imread(hits[0])
if img is None:
continue
loc = eng.locate(img)
crop = img[loc.y : loc.y + loc.h, loc.x : loc.x + loc.w]
if crop.size:
tiles.append(cv2.resize(crop, (320, 96), interpolation=cv2.INTER_AREA))
if tiles:
dest = REPO / "data" / "spaces" / "_cjk_tail_sheet.png"
cv2.imwrite(str(dest), np.vstack(tiles))
print(f"\ncontact sheet ({len(tiles)} crops, score >= {thresh:.3f}) -> {dest}")
print("scores: " + ", ".join(f"{r['tail_score']:.2f}" for r in picks[: len(tiles)]))
if __name__ == "__main__":
main()
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"""Tier B2: detector response curves -- recall vs mark size, contrast, background and aspect.
WHY THIS EXISTS
Every recall number the project quotes rests on found positives: doubao 89% on n=240,
jimeng 71% on n=14, the pill 50% on n=6. Those tell you how the detectors do on the
marks a corpus happened to contain, and nothing about WHERE they fall over. Two bugs
have now shipped in exactly that blind spot:
* `scale_basis` -- doubao detected 0 of 435 LANDSCAPE marks, a 100% miss, because
every fraction was calibrated on portrait captures where width == short side.
* the front-end mismatch -- detection moved to the continuous `tophat` response while
the removal mask still came from the BINARIZED blob, so ~8% of doubao detections
produced an empty mask and removal was a silent no-op.
Both are geometry/plumbing failures at the edge of the operating range, and both were
invisible to a corpus sweep because the corpus is concentrated in the middle of it.
This harness constructs the edges instead of waiting for them to turn up.
THE AGGREGATE HERE IS NOT RECALL
The grid deliberately visits sizes and opacities the engines were never calibrated for,
so a mark counted as missed at size=0.6 is not evidence of a weak detector -- it is the
point of the sweep. Quote the NOMINAL cell (size=1.0, alpha=1.0) as the reference, and
read the per-axis tables for shape. Production recall comes from an unbiased corpus
sample (`scripts/visible_recall_sample.py`), never from here.
WHAT IT MEASURES -- TWO NUMBERS, NOT ONE
`detected` the detector fires.
`maskable` the same call path then yields a NON-EMPTY removal mask.
The second is the one that has no natural home anywhere else. A mark that is detected
but not maskable is reported by `identify` and silently skipped by `visible` -- the user
sees a mark the tool says it removed. Anything that measures only detection scores that
bug as a success. They are reported side by side and their GAP is the headline.
THE CONSTRUCTION
Take a verified-clean corpus image, stamp a real mark onto it with the forward model the
reverse-alpha work established (`stamped = (1-a)*bg + a*white`), and sweep two knobs the
engine's own geometry normally pins:
size multiplies the glyph box the engine would use (a re-rendered or rescaled mark)
alpha multiplies the captured opacity (bold stamp -> faint translucent overlay)
Background texture and frame aspect are not swept -- they come from the corpus and are
recorded, so the grid is crossed with real backgrounds rather than synthetic flats.
WHY EVERY SOURCE ALSO RUNS UNSTAMPED
A recall curve with no false-fire baseline is uninterpretable in the same way a fill
PSNR with no damage baseline is: "detected on 70% of faint marks" is a triumph or a
scandal depending on whether the detector also fires on 70% of the clean frames those
marks were stamped onto. The control runs the identical call path on the identical
image with no stamp.
READING `mask_hit`
Fraction of the stamped glyph box the removal mask covers -- real localization accuracy
for the text marks and gemini, because the mask has to be placed from a detection.
For `jimeng_pill` it is CONSTRUCTED and means nothing: the pill's footprint is a fixed
top-left geometry box, so it covers the stamp by definition. Reported, and flagged.
DATA SAFETY
Corpus images are user uploads: read-only, local analysis, gitignored output under
data/spaces/. Records source filenames and measurements, never image content.
uv run python scripts/detector_response.py --n 12 # trial, measures throughput
uv run python scripts/detector_response.py --n 150 # the real run, resumable
"""
from __future__ import annotations
import argparse
import collections
import json
import math
import os
import sys
from concurrent.futures import ProcessPoolExecutor, as_completed
from pathlib import Path
from typing import Any
import numpy as np
sys.path.insert(0, str(Path(__file__).parent.parent))
sys.path.insert(0, str(Path(__file__).parent))
from fill_quality import SLOT_STAMPABLE, STAMPABLE, clean_sources, stamp_any, texture_of
REPO = Path(__file__).resolve().parents[1]
OUT = REPO / "data" / "spaces" / "_detector_response.jsonl"
# 1.0 = the geometry/opacity the engine's own constants assume. The sweep reaches below
# it (a mark rendered smaller, or a faint translucent overlay -- the class the tophat
# front-end was introduced for) and above it (a larger re-render, or an upscaled upload).
SIZES = (0.6, 0.8, 1.0, 1.3)
ALPHAS = (0.3, 0.5, 0.75, 1.0)
MARKS = (*STAMPABLE, *SLOT_STAMPABLE)
def aspect_of(image: np.ndarray) -> str:
h, w = image.shape[:2]
r = w / max(1, h)
return "portrait" if r < 0.9 else ("landscape" if r > 1.1 else "square")
def _probe(image: np.ndarray, mark_key: str, box: tuple[int, int, int, int] | None) -> dict[str, Any]:
"""Run the product detect -> localize path once and score it.
``box`` is the stamped glyph box, or None for the unstamped control.
"""
from remove_ai_watermarks.watermark_registry import get_mark
mark = get_mark(mark_key)
loc = mark.localize(image, force=False)
mask_px = 0 if loc.mask is None else int(np.count_nonzero(loc.mask))
hit = None
if box is not None and loc.mask is not None:
x, y, w, h = box
inside = loc.mask[y : y + h, x : x + w]
hit = round(float(np.count_nonzero(inside)) / max(1, w * h), 3)
return {
"detected": bool(loc.detected),
"confidence": round(float(loc.confidence), 4),
"maskable": mask_px > 0,
"mask_px": mask_px,
"mask_hit": hit,
}
def _one_source(path_str: str) -> list[dict[str, Any]]:
"""Every (mark, size, alpha) cell for one clean background, plus its controls."""
from remove_ai_watermarks.image_io import imread
base = imread(path_str)
if base is None:
return []
name = Path(path_str).name
asp = aspect_of(base)
h, w = base.shape[:2]
rows: list[dict[str, Any]] = []
for key in MARKS:
common = {"src": name, "mark": key, "aspect": asp, "px": w * h}
# Control first: the same call path on the same frame with nothing stamped.
rows.append({**common, "cell": "control", "size": None, "alpha": None, **_probe(base, key, None)})
for size in SIZES:
for alpha in ALPHAS:
st = stamp_any(base, key, size_mult=size, alpha_mult=alpha)
if st is None:
continue
stamped, box = st
# Texture of the region the mark sits on, from the CLEAN frame -- the
# same median-Sobel proxy the pill's flatness gate uses.
x, y, gw, gh = box
rows.append(
{
**common,
"cell": "stamped",
"size": size,
"alpha": alpha,
"texture": round(texture_of(base[y : y + gh, x : x + gw]), 2),
**_probe(stamped, key, box),
}
)
return rows
def wilson(k: int, n: int, z: float = 1.96) -> tuple[float, float]:
if n == 0:
return (0.0, 0.0)
p, d = k / n, 1 + z * z / n
c = (p + z * z / (2 * n)) / d
hw = z * math.sqrt(p * (1 - p) / n + z * z / (4 * n * n)) / d
return (100 * (c - hw), 100 * (c + hw))
def main() -> None:
ap = argparse.ArgumentParser()
ap.add_argument("--n", type=int, default=150, help="verified-clean source images")
ap.add_argument("--workers", type=int, default=max(1, (os.cpu_count() or 4) - 2))
ap.add_argument("--out", type=Path, default=OUT)
ap.add_argument("--restart", action="store_true")
ap.add_argument("--report-only", action="store_true", help="re-read --out and print the report")
a = ap.parse_args()
if a.report_only:
rows = [json.loads(line) for line in a.out.read_text(encoding="utf-8").splitlines() if line.strip()]
report(rows)
return
if a.restart and a.out.exists():
a.out.unlink()
done: set[str] = set()
if a.out.exists():
with open(a.out, encoding="utf-8") as fh:
for line in fh:
try:
done.add(json.loads(line)["src"])
except Exception: # noqa: S112 -- tolerate a torn last line
continue
print(f"selecting {a.n} verified-clean sources (already measured: {len(done)})...", flush=True)
sources = [p for p in clean_sources(a.n) if p.name not in done]
print(f"to do {len(sources)} workers {a.workers} grid {len(MARKS)}x{len(SIZES)}x{len(ALPHAS)}\n", flush=True)
rows: list[dict[str, Any]] = []
a.out.parent.mkdir(parents=True, exist_ok=True)
with open(a.out, "a", encoding="utf-8") as fh, ProcessPoolExecutor(max_workers=a.workers) as ex:
futures = {ex.submit(_one_source, str(p)): p for p in sources}
for i, fut in enumerate(as_completed(futures), 1):
try:
got = fut.result()
except Exception as e: # a crashed source must not kill the sweep
print(f" source failed: {type(e).__name__}: {e}", flush=True)
continue
for r in got:
fh.write(json.dumps(r) + "\n")
rows += got
if i % 10 == 0:
fh.flush()
print(f" {i}/{len(sources)}", flush=True)
if done: # merge the resumed rows so the report covers the whole file
rows = [json.loads(line) for line in a.out.read_text(encoding="utf-8").splitlines() if line.strip()]
report(rows)
def _rate(rs: list[dict[str, Any]], field: str) -> tuple[float, float, float, int]:
k, n = sum(bool(r[field]) for r in rs), len(rs)
lo, hi = wilson(k, n)
return (100 * k / n if n else 0.0, lo, hi, n)
def report(rows: list[dict[str, Any]]) -> None:
stamped = [r for r in rows if r["cell"] == "stamped"]
control = [r for r in rows if r["cell"] == "control"]
if not stamped:
print("no measurements")
return
srcs = len({r["src"] for r in rows})
print(f"\n{'=' * 84}\nDETECTOR RESPONSE {len(stamped)} stamped cells over {srcs} clean backgrounds\n{'=' * 84}")
# Lead with the nominal cell. The grid deliberately includes sizes and opacities the
# engines were never calibrated for, so an aggregate over the whole grid is an
# adversarial score, NOT production recall -- quoting it as recall would understate
# the detectors badly. The nominal cell is the honest reference point: the mark at the
# exact geometry and opacity the engine assumes, on a real clean background.
print("\nNOMINAL CELL (size=1.0, alpha=1.0) -- a mark exactly as the engine expects it.")
print("Read every other number against THIS, not as production recall: the grid is")
print("adversarial by design and its aggregate is not a recall figure.\n")
print(f"{'mark':13s} {'n':>5s} {'detected':>10s} {'maskable':>10s}")
for key in MARKS:
rs = [r for r in stamped if r["mark"] == key and r["size"] == 1.0 and r["alpha"] == 1.0]
if rs:
print(f"{key:13s} {len(rs):5d} {_rate(rs, 'detected')[0]:9.1f}% {_rate(rs, 'maskable')[0]:9.1f}%")
print("\n\nFALSE FIRE on the unstamped controls (the baseline every recall below is read against)\n")
print(f"{'mark':13s} {'n':>5s} {'fires':>8s} {'95% CI':>16s}")
for key in MARKS:
rs = [r for r in control if r["mark"] == key]
if rs:
pct, lo, hi, n = _rate(rs, "detected")
print(f"{key:13s} {n:5d} {pct:7.1f}% {f'{lo:.1f}-{hi:.1f}':>16s}")
print("\n\nDETECTED vs MASKABLE by mark. The GAP is the silent-no-op rate:")
print("a mark counted here as detected-but-not-maskable is reported by `identify` and")
print("skipped by `visible`, so the user is told it was removed when it was not.\n")
print(f"{'mark':13s} {'n':>6s} {'detected':>10s} {'maskable':>10s} {'gap':>7s} {'mask_hit':>9s}")
for key in MARKS:
rs = [r for r in stamped if r["mark"] == key]
if not rs:
continue
det = [r for r in rs if r["detected"]]
d, m = _rate(rs, "detected")[0], _rate(rs, "maskable")[0]
gap = (100 * sum(1 for r in det if not r["maskable"]) / len(det)) if det else 0.0
hits = [r["mask_hit"] for r in det if r["mask_hit"] is not None]
note = " (constructed)" if key == "jimeng_pill" else ""
hv = f"{float(np.median(hits)):.2f}" if hits else "-"
print(f"{key:13s} {len(rs):6d} {d:9.1f}% {m:9.1f}% {gap:6.1f}% {hv:>9s}{note}")
for axis, label in (("alpha", "CONTRAST (alpha multiplier)"), ("size", "SIZE (glyph box multiplier)")):
print(f"\n\nRECALL BY {label} -- 1.0 is the geometry/opacity the engine assumes\n")
vals = sorted({r[axis] for r in stamped})
print(f"{'mark':13s}" + "".join(f"{v:>12}" for v in vals))
for key in MARKS:
cells = []
for v in vals:
rs = [r for r in stamped if r["mark"] == key and r[axis] == v]
cells.append(f"{_rate(rs, 'detected')[0]:10.0f}%" if rs else f"{'-':>11s}")
print(f"{key:13s}" + "".join(f"{c:>12}" for c in cells))
print("\n\nRECALL BY FRAME ASPECT -- the axis the `scale_basis` bug lived on\n")
asps = ["portrait", "square", "landscape"]
print(f"{'mark':13s}" + "".join(f"{x:>14s}" for x in asps))
for key in MARKS:
cells = []
for asp in asps:
rs = [r for r in stamped if r["mark"] == key and r["aspect"] == asp]
cells.append(f"{_rate(rs, 'detected')[0]:.0f}% (n={len(rs)})" if rs else "-")
print(f"{key:13s}" + "".join(f"{c:>14s}" for c in cells))
tex = sorted(r["texture"] for r in stamped if "texture" in r)
if tex:
t1, t2 = tex[len(tex) // 3], tex[2 * len(tex) // 3]
print(f"\n\nRECALL BY BACKGROUND TEXTURE (terciles at {t1:.1f} / {t2:.1f} median-Sobel)\n")
print(f"{'mark':13s}" + "".join(f"{x:>14s}" for x in ("flat", "mid", "textured")))
for key in MARKS:
cells = []
for lo, hi in ((-1, t1), (t1, t2), (t2, 1e9)):
rs = [r for r in stamped if r["mark"] == key and lo < r.get("texture", -2) <= hi]
cells.append(f"{_rate(rs, 'detected')[0]:.0f}% (n={len(rs)})" if rs else "-")
print(f"{key:13s}" + "".join(f"{c:>14s}" for c in cells))
worst = collections.Counter((r["mark"], r["size"], r["alpha"]) for r in stamped if not r["detected"]).most_common(8)
if worst:
print("\n\nWORST CELLS (most misses)\n")
for (mark, size, alpha), n in worst:
print(f" {mark:13s} size={size} alpha={alpha} {n} misses")
if __name__ == "__main__":
main()
+46 -24
View File
@@ -89,8 +89,31 @@ def engine_for(mark_key: str) -> Any:
return cls()
def stamp(image: np.ndarray, mark_key: str) -> tuple[np.ndarray, tuple[int, int, int, int]] | None:
"""Composite a mark's alpha glyph into its canonical corner. Returns (stamped, bbox)."""
def composite(image: np.ndarray, alpha: np.ndarray, x: int, y: int) -> np.ndarray:
"""The single forward model every stamp uses: ``stamped = (1-a)*bg + a*white``.
``alpha`` is float and clipped to [0,1] here, so a caller may pre-multiply it by an
opacity factor without worrying about overflow. Shared by ``stamp``/``stamp_slot``
here and by ``scripts/detector_response.py`` (which imports it) so the model is
written ONCE.
"""
gh, gw = alpha.shape[:2]
out = image.copy()
roi = out[y : y + gh, x : x + gw].astype(np.float32)
a3 = np.clip(alpha, 0.0, 1.0)[..., None]
out[y : y + gh, x : x + gw] = np.clip(roi * (1 - a3) + 255.0 * a3, 0, 255).astype(np.uint8)
return out
def stamp(
image: np.ndarray, mark_key: str, *, size_mult: float = 1.0, alpha_mult: float = 1.0
) -> tuple[np.ndarray, tuple[int, int, int, int]] | None:
"""Composite a mark's alpha glyph into its canonical corner. Returns (stamped, bbox).
``size_mult`` scales the glyph box off the engine's nominal geometry and ``alpha_mult``
its opacity -- both default to 1.0 (the geometry the engine assumes), and
`scripts/detector_response.py` sweeps them to build response curves.
"""
from remove_ai_watermarks._text_mark_engine import load_alpha_template
engine = engine_for(mark_key)
@@ -101,19 +124,15 @@ def stamp(image: np.ndarray, mark_key: str) -> tuple[np.ndarray, tuple[int, int,
loc = engine.locate(image)
base = engine.scale_base(image)
gw = max(cfg.min_gw, int(cfg.alpha_width_frac * base))
gh = max(4, int(cfg.alpha_height_frac * base))
gw = max(cfg.min_gw, int(cfg.alpha_width_frac * base * size_mult))
gh = max(4, int(cfg.alpha_height_frac * base * size_mult))
if gw < 8 or gh < 4 or gw > loc.w or gh > loc.h:
return None
a = cv2.resize(alpha, (gw, gh), interpolation=cv2.INTER_AREA).astype(np.float32)
a = cv2.resize(alpha, (gw, gh), interpolation=cv2.INTER_AREA).astype(np.float32) * alpha_mult
x = loc.x + (loc.w - gw) // 2
y = loc.y + (loc.h - gh) // 2
out = image.copy()
roi = out[y : y + gh, x : x + gw].astype(np.float32)
a3 = a[..., None]
out[y : y + gh, x : x + gw] = np.clip(roi * (1 - a3) + 255.0 * a3, 0, 255).astype(np.uint8)
return out, (x, y, gw, gh)
return composite(image, a, x, y), (x, y, gw, gh)
def _slot_alpha(mark_key: str) -> np.ndarray | None:
@@ -134,12 +153,15 @@ def _slot_alpha(mark_key: str) -> np.ndarray | None:
return None
def stamp_slot(image: np.ndarray, mark_key: str) -> tuple[np.ndarray, tuple[int, int, int, int]] | None:
def stamp_slot(
image: np.ndarray, mark_key: str, *, size_mult: float = 1.0, alpha_mult: float = 1.0
) -> tuple[np.ndarray, tuple[int, int, int, int]] | None:
"""Stamp a mark into its OWN default footprint slot (the `--no-detect` geometry).
Used for gemini and the pill, which have no bundled alpha asset with corner
fractions. The mark is fitted into the middle of its slot so the fill has to
recover the same kind of region it would in production.
recover the same kind of region it would in production. ``size_mult``/``alpha_mult``
match ``stamp`` (both default to 1.0).
"""
from remove_ai_watermarks.watermark_registry import get_mark
@@ -154,21 +176,21 @@ def stamp_slot(image: np.ndarray, mark_key: str) -> tuple[np.ndarray, tuple[int,
return None
y0, y1, x0, x1 = int(ys.min()), int(ys.max()), int(xs.min()), int(xs.max())
bw, bh = x1 - x0 + 1, y1 - y0 + 1
gw, gh = max(8, int(bw * 0.7)), max(8, int(bh * 0.7))
if gw < 8 or gh < 8 or gw > image.shape[1] or gh > image.shape[0]:
return None
a = cv2.resize(alpha, (gw, gh), interpolation=cv2.INTER_AREA).astype(np.float32)
a = np.clip(a, 0.0, 1.0)
gw, gh = max(8, int(bw * 0.7 * size_mult)), max(8, int(bh * 0.7 * size_mult))
a = cv2.resize(alpha, (gw, gh), interpolation=cv2.INTER_AREA).astype(np.float32) * alpha_mult
x, y = x0 + (bw - gw) // 2, y0 + (bh - gh) // 2
out = image.copy()
roi = out[y : y + gh, x : x + gw].astype(np.float32)
a3 = a[..., None]
out[y : y + gh, x : x + gw] = np.clip(roi * (1 - a3) + 255.0 * a3, 0, 255).astype(np.uint8)
return out, (x, y, gw, gh)
# A large size_mult can grow the glyph past its slot and push x/y negative; guard so
# composite never writes out of bounds (numpy would wrap a negative index silently).
if x < 0 or y < 0 or x + gw > image.shape[1] or y + gh > image.shape[0]:
return None
return composite(image, a, x, y), (x, y, gw, gh)
def stamp_any(image: np.ndarray, mark_key: str) -> tuple[np.ndarray, tuple[int, int, int, int]] | None:
return stamp(image, mark_key) if mark_key in STAMPABLE else stamp_slot(image, mark_key)
def stamp_any(
image: np.ndarray, mark_key: str, *, size_mult: float = 1.0, alpha_mult: float = 1.0
) -> tuple[np.ndarray, tuple[int, int, int, int]] | None:
fn = stamp if mark_key in STAMPABLE else stamp_slot
return fn(image, mark_key, size_mult=size_mult, alpha_mult=alpha_mult)
def clean_sources(n: int, seed: int = 11) -> list[Path]:
+305
View File
@@ -0,0 +1,305 @@
"""How much recall is the coarse scale ladder costing, and what would a denser one cost?
THE FINDING THIS MEASURES
`_tophat_score` sweeps three rungs -- (0.8, 1.0, 1.25) -- and the `binary` front-end
sweeps none at all. Measured on stamped marks over controlled backgrounds
(`scripts/detector_response.py`), the response is a COMB: doubao scores 0.99 exactly at
each rung and collapses to 0.37-0.48 between them, against a 0.50 gate. So a mark whose
rendered size lands mid-gap is missed at FULL contrast. Jimeng (binary, one nominal
size) holds a single 0.90-1.20 lobe; samsung only 0.95-1.05.
WHY A SYNTHETIC SWEEP IS NOT ENOUGH TO JUSTIFY A FIX
Dead zones only cost recall if real marks land in them. The fractions were calibrated on
real captures, so it is entirely possible that real marks cluster at ratio 1.0 and the
gaps are never visited. That question is not answerable by stamping -- it needs the
corpus.
THE MEASUREMENT
Positives are images carrying INDEPENDENT vendor provenance (TC260 / C2PA metadata
naming the vendor), which is evidence that does not come from the pixel detector we are
grading -- the same discriminator that settled the pill gate. For every such image the
detector currently MISSES, rescore at a dense ladder and ask whether it would now cross
the gate, and at which scale.
Negatives are images with NO metadata signal at all. That is deliberately NOT "and no
mark was detected": defining the set by the detector's own verdict would make its
false-fire rate 0 by construction and the comparison vacuous. The cost is that a
metadata-stripped screenshot of a marked image sits in the negative set and its correct
detection is counted as a false fire -- but that impurity is identical under both
ladders, so the DELTA between them, which is what the fix is judged on, stays sound.
Two more impurities to keep in view when reading the positive arm. Provenance says the
vendor produced the file, not that a visible mark is on it. And the TC260 label names no
specific vendor, so `visible_provenance` maps it to BOTH doubao and jimeng -- a "doubao
positive" may carry a jimeng mark or none. Both inflate the miss count, so the recovery
percentage is an upper bound on what a denser ladder buys.
DATA SAFETY
Corpus images are user uploads: read-only, local analysis, gitignored output.
uv run python scripts/ladder_headroom.py --mark doubao --n 4000
"""
from __future__ import annotations
import argparse
import collections
import glob
import json
import math
import os
import random
import sys
from concurrent.futures import ProcessPoolExecutor, as_completed
from pathlib import Path
from typing import Any
import cv2
import numpy as np
sys.path.insert(0, str(Path(__file__).parent.parent))
REPO = Path(__file__).resolve().parents[1]
CORPUS = REPO / "data" / "spaces" / "originals"
OUT = REPO / "data" / "spaces" / "_ladder_headroom.jsonl"
# The rungs the product ships today, and the dense ladder under evaluation. The dense one
# is geometric with a ~6% step, chosen from the measured half-width of a rung's lobe
# (doubao holds >=0.5 for about +/-6% around each peak), so no gap is left uncovered.
SHIPPED = (0.8, 1.0, 1.25)
LADDERS: dict[str, tuple[float, ...]] = {
# A geometric ~6% step across the whole plausible range. Measures the CEILING of what
# any ladder change can buy, and the worst case of what it costs in false fires.
"dense": tuple(round(0.70 * (1.06**i), 4) for i in range(13)), # 0.70 .. ~1.49
# The targeted alternative. On the full run, 26 of 28 recoveries came from ONE rung
# (~1.116) and 22 of 28 were LANDSCAPE frames -- that is a geometry gap, not a density
# gap, so the honest comparison is one extra rung against thirteen.
"plus_one": (0.8, 1.0, 1.1157, 1.25),
"shipped": SHIPPED,
}
DENSE = LADDERS["dense"]
# Score every rung any candidate ladder might use and store them all, so a new candidate
# is evaluated by re-reading the JSONL instead of re-running the hour-long sweep.
PROBE_SCALES: tuple[float, ...] = tuple(sorted({s for rungs in LADDERS.values() for s in rungs}))
def wilson(k: int, n: int, z: float = 1.96) -> tuple[float, float]:
if n == 0:
return (0.0, 0.0)
p, d = k / n, 1 + z * z / n
c = (p + z * z / (2 * n)) / d
hw = z * math.sqrt(p * (1 - p) / n + z * z / (4 * n * n)) / d
return (100 * (c - hw), 100 * (c + hw))
def score_at_scales(engine: Any, image: np.ndarray, scales: tuple[float, ...]) -> dict[float, float]:
"""`_tophat_score`'s inner loop, opened up so the ladder is a parameter.
Deliberately reaches into the engine (`tophat_response`, `_glyph_silhouette`): a
measurement script may, product code may not. Kept a faithful copy of the shipped
scoring -- if it drifts, the numbers below stop describing the product.
"""
c = engine.config
loc = engine.locate(image)
resp = engine.tophat_response(image, loc)
sil = engine._glyph_silhouette()
if resp is None or sil is None:
return {}
base = engine.scale_base(image)
out: dict[float, float] = {}
for scale in scales:
gw = max(c.min_gw, int(c.alpha_width_frac * base * scale))
gh = max(4, int(c.alpha_height_frac * base * scale))
if gw >= resp.shape[1] or gh >= resp.shape[0]:
continue
tmpl = cv2.resize(sil, (gw, gh), interpolation=cv2.INTER_AREA).astype(np.float32)
if c.template_blur > 0:
tmpl = cv2.GaussianBlur(tmpl, (0, 0), sigmaX=c.template_blur, sigmaY=c.template_blur)
out[scale] = float(cv2.matchTemplate(resp, tmpl.astype(np.uint8), cv2.TM_CCOEFF_NORMED).max())
return out
def _one(args: tuple[str, str]) -> dict[str, Any] | None:
path_str, mark_key = args
from remove_ai_watermarks.api import visible_provenance
from remove_ai_watermarks.identify import identify
from remove_ai_watermarks.image_io import imread
from remove_ai_watermarks.watermark_registry import get_mark
path = Path(path_str)
try:
prov = visible_provenance(path)
except Exception:
return None
positive = mark_key in prov
if not positive:
# A negative is a frame with NO metadata signal at all -- evidence independent of
# the detector being graded. Do NOT also require that no mark was detected: that
# defines the negative set by the very verdict under test, and "false fire today"
# would then be 0 by construction on every run.
try:
if identify(path, check_visible=False).signals:
return None
except Exception:
return None
img = imread(path_str)
if img is None or min(img.shape[:2]) < 200:
return None
mark = get_mark(mark_key)
det = mark.detect(img)
import importlib
mod = importlib.import_module(f"remove_ai_watermarks.{mark_key}_engine")
cls = next(
o for n, o in vars(mod).items() if isinstance(o, type) and n.endswith("Engine") and n != "TextMarkEngine"
)
engine = cls()
scores = score_at_scales(engine, img, PROBE_SCALES)
if not scores:
return None
gate = engine.config.detect_ncc_threshold
dense = {s: v for s, v in scores.items() if s in LADDERS["dense"]}
best_scale = max(dense, key=lambda s: dense[s]) if dense else 0.0
h, w = img.shape[:2]
return {
"src": path.name,
"arm": "positive" if positive else "negative",
"detected_now": bool(det.detected),
"conf_now": round(float(det.confidence), 4),
"gate": gate,
# Every rung, so a new candidate ladder is evaluated by re-reading this file.
"scores": {str(s): round(v, 4) for s, v in scores.items()},
"dense_best": round(dense[best_scale], 4) if dense else 0.0,
"dense_best_scale": best_scale,
"dense_crosses": bool(dense) and dense[best_scale] >= gate,
"aspect": "portrait" if w / h < 0.9 else ("landscape" if w / h > 1.1 else "square"),
}
def main() -> None:
ap = argparse.ArgumentParser()
# doubao only, and that is not laziness. `score_at_scales` reproduces the TOPHAT
# front-end, which is the only one with a ladder to widen; scoring it for jimeng or
# samsung would measure a code path their detectors never run. Doubao is also the one
# mark that declares NO rival, so crossing its NCC gate really is the whole verdict --
# for a mark with rivals, `dense_crosses` would ignore the competitive margin and read
# optimistically. Widening the binary front-end is a separate experiment.
ap.add_argument("--mark", default="doubao", choices=["doubao"])
ap.add_argument("--n", type=int, default=4000, help="corpus files to scan")
ap.add_argument("--workers", type=int, default=max(1, (os.cpu_count() or 4) - 2))
ap.add_argument("--out", type=Path, default=OUT)
ap.add_argument("--report-only", action="store_true")
a = ap.parse_args()
out = a.out.with_name(f"{a.out.stem}_{a.mark}{a.out.suffix}")
if a.report_only:
report([json.loads(x) for x in out.read_text(encoding="utf-8").splitlines() if x.strip()], a.mark)
return
pool = glob.glob(str(CORPUS / "*" / "*"))
random.Random(19).shuffle(pool) # noqa: S311 -- deterministic sampling, not crypto
pool = pool[: a.n]
print(f"mark={a.mark} scanning {len(pool)} corpus files workers={a.workers}")
print(f"shipped ladder {SHIPPED}\ndense ladder {DENSE}\n", flush=True)
rows: list[dict[str, Any]] = []
out.parent.mkdir(parents=True, exist_ok=True)
with open(out, "w", encoding="utf-8") as fh, ProcessPoolExecutor(max_workers=a.workers) as ex:
futures = [ex.submit(_one, (p, a.mark)) for p in pool]
for i, fut in enumerate(as_completed(futures), 1):
try:
rec = fut.result()
except Exception: # noqa: S112 -- one bad file must not kill the sweep
continue
if rec is None:
continue
fh.write(json.dumps(rec) + "\n")
rows.append(rec)
if i % 500 == 0:
fh.flush()
pos = sum(1 for r in rows if r["arm"] == "positive")
print(f" {i}/{len(pool)} usable={len(rows)} (pos={pos})", flush=True)
report(rows, a.mark)
def report(rows: list[dict[str, Any]], mark: str) -> None:
pos = [r for r in rows if r["arm"] == "positive"]
neg = [r for r in rows if r["arm"] == "negative"]
print(f"\n{'=' * 82}\nLADDER HEADROOM mark={mark} positives={len(pos)} verified-clean negatives={len(neg)}")
print(f"{'=' * 82}")
if not pos and not neg:
print("no usable rows")
return
if pos:
miss = [r for r in pos if not r["detected_now"]]
rec = [r for r in miss if r["dense_crosses"]]
now = len(pos) - len(miss)
lo, hi = wilson(len(rec), len(miss)) if miss else (0.0, 0.0)
print("\nPOSITIVE ARM (images whose METADATA names this vendor -- an upper bound,")
print("provenance says the vendor produced the file, not that a mark is visible on it)\n")
print(f" detected today {now:5d} / {len(pos)} ({100 * now / len(pos):.1f}%)")
print(f" of the {len(miss)} misses, the dense ladder crosses the gate on {len(rec)}")
if miss:
print(f" ({100 * len(rec) / len(miss):.1f}%, 95% CI {lo:.1f}-{hi:.1f})")
after = now + len(rec)
print(f" detection would go {100 * now / len(pos):.1f}% -> {100 * after / len(pos):.1f}%")
if rec:
by_scale = collections.Counter(r["dense_best_scale"] for r in rec)
print("\n which rung recovers them (a rung near a SHIPPED one recovering many means")
print(" the gain is the finer STEP, not the wider RANGE):")
for s, n in sorted(by_scale.items()):
near = " <- shipped" if any(abs(s - x) < 0.02 for x in SHIPPED) else ""
print(f" scale {s:<6} {n:4d}{near}")
by_asp = collections.Counter(r["aspect"] for r in rec)
print(f"\n by aspect: {dict(by_asp)}")
if neg:
fires_now = sum(1 for r in neg if r["detected_now"])
fires_dense = sum(1 for r in neg if r["dense_crosses"])
lo0, hi0 = wilson(fires_now, len(neg))
lo1, hi1 = wilson(fires_dense, len(neg))
print("\n\nNEGATIVE ARM (no metadata signal; NOT filtered on the detector's own verdict)\n")
p0, p1 = 100 * fires_now / len(neg), 100 * fires_dense / len(neg)
print(f" false fire today {fires_now:4d} / {len(neg)} {p0:.2f}% (CI {lo0:.2f}-{hi0:.2f})")
print(f" false fire, dense ladder {fires_dense:4d} / {len(neg)} {p1:.2f}% (CI {lo1:.2f}-{hi1:.2f})")
print("\n This is the price. A denser ladder gives a spurious blob more chances to")
print(" match at SOME scale, so the gain above is only real if this line barely moves.")
ladder_table(pos, neg)
def _crosses(row: dict[str, Any], rungs: tuple[float, ...]) -> bool:
"""Would this frame cross its gate on the given ladder, from the stored per-rung scores."""
sc = row.get("scores") or {}
gate = row["gate"]
return any(v >= gate for k, v in sc.items() if float(k) in rungs)
def ladder_table(pos: list[dict[str, Any]], neg: list[dict[str, Any]]) -> None:
"""Every candidate ladder side by side: what it recovers against what it costs."""
if not (pos and neg) or "scores" not in pos[0]:
return # older run without per-rung scores
miss = [r for r in pos if not r["detected_now"]]
base_fire = sum(1 for r in neg if r["detected_now"])
print("\n\nLADDER CANDIDATES -- recovered marks against the false fires they cost\n")
print("A candidate is only worth shipping if the recovered column beats the added-fires")
print("column by enough to survive the base rates: clean frames vastly outnumber marked")
print("ones in real traffic, so a small percentage on the negative arm is a large count.\n")
hdr = f"{'ladder':10s} {'rungs':>6s} {'recovered':>10s} {'of misses':>10s}"
print(f"{hdr} {'false fire':>11s} {'added':>7s} {'ratio':>7s}")
for name, rungs in LADDERS.items():
rec = sum(1 for r in miss if _crosses(r, rungs))
fire = sum(1 for r in neg if _crosses(r, rungs) or r["detected_now"])
added = fire - base_fire
ratio = f"{rec / added:.1f}:1" if added > 0 else ("inf" if rec else "-")
pct = 100 * rec / len(miss) if miss else 0.0
print(f"{name:10s} {len(rungs):6d} {rec:10d} {pct:9.1f}% {100 * fire / len(neg):10.2f}% {added:7d} {ratio:>7s}")
if __name__ == "__main__":
main()
+29
View File
@@ -45,6 +45,35 @@ almost nothing and, at any threshold low enough to fire, fires on arbitrary corn
星绘 additionally has only ONE confirmed example in the corpus, so even a working
front-end could not have its threshold calibrated yet.
UPDATE 2026-07-20: the named blocker is GONE, and the retry is still inconclusive.
`detect_frontend="tophat"` (built later, for doubao) is exactly the "grayscale correlation
on the raw top-hat" this note asked for, so the 2026-07-18 ruling rests on a premise that
no longer holds and must not simply be inherited. Two things were measured against it, and
neither settles the question:
* A GENERIC template of the shared `AI生成` tail -- attractive because GB 45438-2025
guarantees that run across vendors, so one template would cover 千问 / 百度 / 星绘 and
anything compliant that ships next. Measured on the tophat front-end at the shipped
3-rung ladder: a bold 千问 positive scores 0.407 against clean corners at p99 0.298 /
max 0.321. It separates on that one frame, but only by a hair, and a 4-glyph template
is inherently less specific than a 6-glyph one -- the shorter the run, the more
arbitrary corner structure correlates with it.
* The FULL 千问 template on the same front-end scores 0.248 against a clean max of 0.537,
i.e. no separation at all -- WORSE than the generic tail, which is the opposite of
what the specificity argument predicts and is itself a reason to distrust n=1.
The blocker is now EVIDENCE, not architecture: this session found exactly one 千问 and one
百度 positive (both by eyeballing doubao-provenance misses), and the 14 positives quoted
above were not preserved anywhere the current scripts can reach. Nothing should be
registered off a single frame. What it takes: harvest 30+ confirmed positives per vendor
-- `scripts/cjk_tail_probe.py` exists for exactly this, scoring TC260-provenance frames
that no detector fires on and writing a contact sheet of the top scorers to label -- then
calibrate a gate against the clean arm. Two traps worth knowing before repeating this
measurement: score with `alpha_height_frac`, not the silhouette's own aspect ratio (the
latter inflated the clean p99 from 0.30 to 0.58 and made every comparison meaningless),
and keep the ladder at the shipped 3 rungs, since a wide sweep hands clean corners many
extra chances to match.
"""
from __future__ import annotations