fix(invisible): preserve native output dimensions

src/remove_ai_watermarks/invisible_engine.py

@@ -269,7 +269,11 @@ class InvisibleEngine:
             # each stage independently imread/imwrote the full-res output, so a run
             # with several stages PNG-decoded+re-encoded the same image 2-4 times.
             # PNG is lossless, so the single-write output is byte-identical.
-            needs_restore = target is not None  # the input was resized before diffusion
+            # Diffusers rounds native dimensions down to the latent grid (multiples
+            # of 8), even when our own resolution policy did not resize the input.
+            # Route those outputs through the same final resize so --no-polish does
+            # not silently change e.g. 1448x1086 into 1448x1080.
+            needs_restore = target is not None or any(dimension % 8 for dimension in orig_size)
             if humanize > 0.0 or unsharp > 0.0 or adaptive_polish or needs_restore:
                 import cv2
 

tests/test_invisible_engine.py

@@ -2,6 +2,10 @@
 
 from __future__ import annotations
 
+from types import SimpleNamespace
+
+from PIL import Image
+
 from remove_ai_watermarks.invisible_engine import InvisibleEngine, _target_size, is_available
 
 
@@ -31,6 +35,29 @@ class TestInvisibleEngineInit:
         assert InvisibleEngine.DEFAULT_MODEL_ID == "stabilityai/stable-diffusion-xl-base-1.0"
 
 
+class TestNativeOutputSize:
+    """Model-side latent-grid rounding must not change the public output size."""
+
+    def test_no_polish_restores_native_non_multiple_of_eight_size(self, tmp_path):
+        engine = object.__new__(InvisibleEngine)
+
+        def _remove_watermark(image_path, output_path=None, **_kwargs):
+            out = output_path or image_path.with_stem(image_path.stem + "_clean")
+            # Model-side latent-grid rounding: 18px becomes 16px.
+            Image.open(image_path).crop((0, 0, 24, 16)).save(out)
+            return out
+
+        engine._remover = SimpleNamespace(remove_watermark=_remove_watermark)
+        engine._progress_callback = None
+        src = tmp_path / "src.png"
+        out = tmp_path / "out.png"
+        Image.new("RGB", (24, 18), (128, 128, 128)).save(src)
+
+        engine.remove_watermark(src, out, min_resolution=0, adaptive_polish=False)
+
+        assert Image.open(out).size == (24, 18)
+
+
 class TestTargetSize:
     """Regression guard for the native-resolution decision (issues #10 / #15).