After orientation detection, the frontend now automatically calls the
page-split endpoint. When a double-page book spread is detected, two
sub-sessions are created and each goes through the full pipeline
(deskew/dewarp/crop) independently — essential because each page of a
spread tilts differently due to the spine.
Frontend changes:
- StepOrientation: calls POST /page-split after orientation, shows
split info ("Doppelseite erkannt"), notifies parent of sub-sessions
- page.tsx: distinguishes page-split sub-sessions (current_step < 5)
from crop-based sub-sessions (current_step >= 5). Page-split subs
only skip orientation, not deskew/dewarp/crop.
- page.tsx: handleOrientationComplete opens first sub-session when
page-split was detected
Backend changes (orientation_crop_api.py):
- page-split endpoint falls back to original image when orientation
rotated a landscape spread to portrait
- start_step parameter: 1 if split from original, 2 if from oriented
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Each page of a double-page scan tilts differently due to the book spine.
The new POST /page-split endpoint detects spreads after orientation and
creates sub-sessions that go through the full pipeline (deskew, dewarp,
crop, etc.) individually, so each page gets its own deskew correction.
Also fixes border-strip filter incorrectly removing German translation
words by adding a decorative-strip validation check.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
When a book scan (double-page spread) is detected during the crop step,
the system automatically:
1. Detects vertical center gaps (spine area) via ink density projection
2. Splits into N page sub-sessions (reusing existing sub-session mechanism)
3. Individually crops each page (removing its own borders)
4. Returns sub-session IDs for downstream pipeline processing
Detection: landscape images (w > h * 1.15), vertical gap < 15% peak
density in center region (25-75%), gap width >= 0.8% of image width.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
