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remove-ai-watermarks/src/remove_ai_watermarks/doubao_engine.py
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"""Doubao visible watermark detector/localizer.
Doubao (ByteDance) stamps every generated image with a visible "豆包AI生成"
(Doubao AI generated) text strip in the bottom-right corner -- the explicit AIGC
label mandated by China's TC260 standard, a near-white semi-transparent overlay.
Detection matches the bundled glyph silhouette against the corner candidate; removal
is the shared **localize -> fill** (the glyph-bbox :meth:`footprint_mask` feeds
``region_eraser``), NOT reverse-alpha. This module shares
:class:`remove_ai_watermarks._text_mark_engine.TextMarkEngine` and
supplies only Doubao's tuned :class:`TextMarkConfig` (bottom-right corner,
``assets/doubao_alpha.png`` -- the detection silhouette, rebuilt by
``scripts/visible_alpha_solve.py``). Arbitrary-region inpainting still lives in
``region_eraser`` / the ``erase`` command.
"""
# The module-level _alpha_template / _glyph_silhouette / _template_match_score below
# are thin test-facing shims (imported by tests/), so pyright's src-only pass sees them
# as unused; the use is cross-module.
# pyright: reportUnusedFunction=false
from __future__ import annotations
from typing import TYPE_CHECKING, Any
from remove_ai_watermarks import _text_mark_engine
from remove_ai_watermarks._text_mark_engine import TextMarkConfig, TextMarkDetection, TextMarkEngine
if TYPE_CHECKING:
from pathlib import Path
from numpy.typing import NDArray
# Locate geometry as a fraction of image WIDTH (the mark scales with width, anchored
# bottom-right). The box is GENEROUSLY wider than the mark and reaches close to the
# corner so a per-image re-rasterization shift stays inside the NCC alignment search.
WM_WIDTH_FRAC = 0.22
WM_HEIGHT_FRAC = 0.075
MARGIN_RIGHT_FRAC = 0.004
MARGIN_BOTTOM_FRAC = 0.004
# Glyph appearance: a light, low-saturation gray rendered brighter than the local
# background (white top-hat), so a white-paper document is left untouched.
MAX_SATURATION = 55 # max channel spread to count a pixel as "grayish"
LOGO_MIN_LUMA = 150 # glyphs are at least this bright in absolute terms
TOPHAT_DELTA = 12 # glyph must exceed the local background by this many levels
# Shape-consistent detection: match the bundled alpha glyph silhouette against the
# corner candidate via TM_CCOEFF_NORMED (keys on glyph SHAPE, not coverage; #23).
DETECT_MIN_COVERAGE = 0.04
# NOTE: this gate is FRONT-END SPECIFIC. The continuous top-hat front-end scores higher
# overall than the binary one (mean 0.809 vs 0.723 on the same 90 positives), so the
# binary-era 0.40 left the provenance-relaxed gate (x0.7) far too low and admitted false
# fires. Calibrated on the 240-image unbiased recall sample, full auto path:
#
# gate relaxed recall precision true false
# 0.40 0.280 96% 91% 86 8
# 0.45 0.315 94% 93% 85 6
# 0.50 0.350 92% 99% 83 1 <- chosen
# 0.60 0.420 87% 99% 78 1
#
# 0.50 beats the binary front-end on recall (92% vs 89%) at identical precision (99%),
# which is the only reason the front-end switch is worth it. Do not port this number to
# a binary-front-end mark; re-calibrate per front-end.
DETECT_NCC_THRESHOLD = 0.50
# Detection-silhouette geometry, emitted by scripts/visible_alpha_solve.py at the
# captured width. Sizes the glyph silhouette for the TM_CCOEFF_NORMED detection match
# (removal is the template-free glyph-bbox footprint mask, not this template).
_ALPHA_NATIVE_WIDTH = 2048
_ALPHA_WIDTH_FRAC = 0.1636 # asset width / image width -- sizes the detection silhouette
_ALPHA_HEIGHT_FRAC = 0.0405
_CONFIG = TextMarkConfig(
name="Doubao",
asset_name="doubao_alpha.png",
corner="br",
margin_floor=4,
width_frac=WM_WIDTH_FRAC,
height_frac=WM_HEIGHT_FRAC,
margin_x_frac=MARGIN_RIGHT_FRAC,
margin_bottom_frac=MARGIN_BOTTOM_FRAC,
max_saturation=MAX_SATURATION,
logo_min_luma=LOGO_MIN_LUMA,
tophat_delta=TOPHAT_DELTA,
morph_open_size=5,
detect_min_coverage=DETECT_MIN_COVERAGE,
detect_ncc_threshold=DETECT_NCC_THRESHOLD,
detect_frontend="tophat",
scale_basis="short", # measured: recovers 56% of landscape misses (see scale_base)
# No rival margin: measured 2026-07-18, the symmetric gate cost Doubao 7 genuine
# detections to prevent 5 false ones (1.4:1 against). Doubao's absolute detector
# is already 86% precise, so it has nothing to buy; Jimeng's is 38% and gains 25pp
# for free. The confusion is asymmetric, so the remedy is too.
alpha_width_frac=_ALPHA_WIDTH_FRAC,
alpha_height_frac=_ALPHA_HEIGHT_FRAC,
min_gw=8,
)
# Doubao-specific aliases for the shared detection result/engine.
DoubaoDetection = TextMarkDetection
def _alpha_template() -> NDArray[Any] | None:
"""The bundled Doubao alpha template (float [0,1]), or None."""
return _text_mark_engine.load_alpha_template(_CONFIG.asset_name)
def _glyph_silhouette() -> NDArray[Any] | None:
"""Binary "豆包AI生成" silhouette (255 = glyph) from the alpha map, or None."""
return _text_mark_engine.glyph_silhouette(_CONFIG.asset_name)
def _template_match_score(box_mask: NDArray[Any], scale_base: int) -> float:
"""TM_CCOEFF_NORMED of the Doubao glyph silhouette against ``box_mask``."""
return _text_mark_engine.template_match_score(box_mask, scale_base, _CONFIG)
class DoubaoEngine(TextMarkEngine):
"""Detect/localize the visible Doubao "豆包AI生成" watermark (locate -> mask; mask feeds the fill)."""
def __init__(self) -> None:
super().__init__(_CONFIG)
def load_image_bgr(path: str | Path) -> NDArray[Any]:
"""Read an image as BGR ndarray (helper for scripts/tests)."""
from remove_ai_watermarks import image_io
img = image_io.imread(path)
if img is None:
raise FileNotFoundError(f"Failed to read image: {path}")
return img