fix(invisible): ctrlregen defaults to clean-noise strength, not the SDXL 0.10

The ctrlregen profile inherited the SDXL img2img --strength default (0.10), a
near-identity pass that loaded ControlNet + DINOv2-giant and barely changed the
image -- a no-op for removal. resolve_strength() now resolves an unset strength
per profile: 0.10 for the SDXL default, CTRLREGEN_DEFAULT_STRENGTH (1.0,
clean-noise) for ctrlregen. It checks `is None` rather than falsiness, so an
explicit 0.0 is respected (the old `strength or DEFAULT` swallowed it).

Research basis: CtrlRegen (ICLR 2025, arXiv:2410.05470) removes robust
watermarks by regenerating from clean Gaussian noise; partial-noise img2img
retains watermark info that diffuses back, so a high (clean-noise) strength is
the lever, not a knob on the light SDXL pass. CLI wiring (--strength default
None) lands with the cli refactor.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/remove_ai_watermarks/invisible_engine.py

@@ -19,8 +19,6 @@ import warnings
 from pathlib import Path
 from typing import TYPE_CHECKING
 
-from remove_ai_watermarks.noai.watermark_profiles import DEFAULT_STRENGTH
-
 if TYPE_CHECKING:
     from collections.abc import Callable
 
@@ -135,7 +133,8 @@ class InvisibleEngine:
         Args:
             image_path: Path to the watermarked image.
             output_path: Output path (None = overwrite source).
-            strength: Denoising strength (0.0-1.0). None -> DEFAULT_STRENGTH (0.10).
+            strength: Denoising strength (0.0-1.0). None -> profile default
+                (0.10 for SDXL, 1.0 clean-noise for ctrlregen).
             steps: Number of denoising steps.
             guidance_scale: Classifier-free guidance scale.
             seed: Random seed for reproducibility.
@@ -281,7 +280,7 @@ class InvisibleEngine:
         self,
         input_dir: Path,
         output_dir: Path,
-        strength: float = DEFAULT_STRENGTH,
+        strength: float | None = None,
         steps: int = 50,
     ) -> list[Path]:
         """Remove invisible watermarks from all images in a directory."""

src/remove_ai_watermarks/noai/watermark_profiles.py

@@ -21,6 +21,33 @@ CTRLREGEN_MODEL_ID = "yepengliu/ctrlregen"
 # knob is this default plus the per-call `--strength` override.)
 DEFAULT_STRENGTH = 0.10
 
+# CtrlRegen removes watermarks by regenerating from (near) clean Gaussian noise,
+# NOT by the light-touch partial-noise img2img the SDXL default uses. The research
+# is explicit (CtrlRegen, ICLR 2025, arXiv:2410.05470): partial-noise regeneration
+# "struggles with high-perturbation watermarks" because a small noise step "retains"
+# watermark information that diffuses back into the output; the fix is to start from
+# clean noise. With the StableDiffusionControlNetImg2ImgPipeline that maps to a high
+# strength (~1.0 = full noise at the first timestep, structure held by the canny
+# ControlNet + DINOv2 IP-Adapter, not by the watermarked latent). So the ctrlregen
+# profile must NOT inherit the SDXL 0.10 default -- at 0.10 it loads ControlNet +
+# DINOv2-giant and then barely changes the image (a no-op for removal). Tunable via
+# `--strength`; lower it to trade removal strength for fidelity (the CtrlRegen+ regime).
+CTRLREGEN_DEFAULT_STRENGTH = 1.0
+
+
+def resolve_strength(strength: float | None, profile: str) -> float:
+    """Resolve the denoising strength, applying the profile-specific default when unset.
+
+    ``None`` means "the user did not pass ``--strength``": the SDXL default profile
+    resolves to ``DEFAULT_STRENGTH`` (a light SynthID-tuned touch), while ``ctrlregen``
+    resolves to ``CTRLREGEN_DEFAULT_STRENGTH`` (clean-noise regeneration). An explicit
+    value always wins. Shared by the CLI (for display) and the engine (for execution)
+    so the two never disagree.
+    """
+    if strength is not None:
+        return strength
+    return CTRLREGEN_DEFAULT_STRENGTH if profile == "ctrlregen" else DEFAULT_STRENGTH
+
 
 def get_model_id_for_profile(profile: str) -> str:
     """Map CLI model profile names to concrete Hugging Face model IDs."""

src/remove_ai_watermarks/noai/watermark_remover.py

@@ -33,6 +33,7 @@ from remove_ai_watermarks.noai.watermark_profiles import (
     DEFAULT_MODEL_ID,
     DEFAULT_STRENGTH,
     detect_model_profile,
+    resolve_strength,
 )
 
 logger = logging.getLogger(__name__)
@@ -474,7 +475,7 @@ class WatermarkRemover:
         if output_path is None:
             output_path = image_path
 
-        strength = strength or self.DEFAULT_STRENGTH
+        strength = resolve_strength(strength, self.model_profile)
 
         if not 0.0 <= strength <= 1.0:
             raise ValueError(f"Strength must be between 0.0 and 1.0, got {strength}")
@@ -894,12 +895,16 @@ class WatermarkRemover:
 def remove_watermark(
     image_path: Path,
     output_path: Path | None = None,
-    strength: float = DEFAULT_STRENGTH,
+    strength: float | None = None,
     model_id: str | None = None,
     device: str | None = None,
     hf_token: str | None = None,
 ) -> Path:
-    """Convenience function to remove watermark from an image."""
+    """Convenience function to remove watermark from an image.
+
+    ``strength=None`` lets the profile pick its default (0.10 for SDXL, clean-noise
+    1.0 for ctrlregen); pass a value to override.
+    """
     remover = WatermarkRemover(model_id=model_id, device=device, hf_token=hf_token)
     return remover.remove_watermark(
         image_path=image_path,