diff --git a/docs/guide.md b/docs/guide.md
index 0a04e4c..435787c 100644
--- a/docs/guide.md
+++ b/docs/guide.md
@@ -44,10 +44,11 @@ off.
    one back.
 4. **Set the content rectangle.** Drag the blue edges so they hold the music and
    nothing else. This is the horizontal crop for every slice on the page.
-5. **Set black and white points.** Pull the *White point* down until the paper
-   goes pure white and its texture disappears; pull *Black point* up until the
-   notes are solid black rather than grey mush. Scans need this; clean digital
-   PDFs usually don't.
+5. **Check black and white points.** These arrive proposed from the scan, like
+   the cuts do. If the paper still shows texture, pull *White point* down; if the
+   notes look grey rather than solid, pull *Black point* up. Getting this wrong
+   is the one mistake you cannot see until the bundle is on the tablet — grey ink
+   becomes half-transparent ink, and nothing downstream can rescue it.
 
 Page Up / Page Down move between pages. Levels carry over from the previous
 page, so a consistent scan only needs setting once.
diff --git a/docs/spec.md b/docs/spec.md
index 49e05a3..65b4531 100644
--- a/docs/spec.md
+++ b/docs/spec.md
@@ -236,6 +236,14 @@ point just under the paper's luminance and the paper vanishes completely; set th
 black point at the ink's darkest and notes go solid. It is also the single
 biggest lever on output size.
 
+**Detection proposes both**, like it proposes cuts and skew, because the default
+0–255 is the one setting whose harm is invisible until the bundle is on a tablet.
+Notation is two-tone, so Otsu's split between ink and paper is the measurement;
+the points sit halfway from it to each end of the range, leaving the ramp between
+them as the antialiasing. A page already scanned bilevel has no interior split —
+Otsu degenerates to 0 there — and is left at 0–255. The proposal is per page and
+the median becomes the song's, so a near-blank page cannot set it.
+
 Adaptive methods (CLAHE, adaptive thresholding) are the trap — tuned for text,
 they eat the thin stuff on notation: hairpin tips, slur ends, ledger lines,
 tapered beams. A global LUT whose effect you can see beats a local algorithm you
diff --git a/noteman_slicer/detect.py b/noteman_slicer/detect.py
index 01f9ccb..bb57b6e 100644
--- a/noteman_slicer/detect.py
+++ b/noteman_slicer/detect.py
@@ -65,6 +65,7 @@ class PageDetection:
     systems: list[System] = field(default_factory=list)
     cuts: list[int] = field(default_factory=list)
     content: tuple[float, float, float, float] = (0.0, 0.0, 1.0, 1.0)
+    levels: tuple[int, int] = (0, 255)
 
     @property
     def bracketless(self) -> bool:
@@ -292,6 +293,26 @@ def staff_height(gray: np.ndarray, top: int, bottom: int) -> float | None:
     return float(np.median(intra) * 4)  # 5 lines, 4 spaces
 
 
+def ink_levels(gray: np.ndarray) -> tuple[int, int]:
+    """Black and white points that put the ink on black and the paper on white.
+
+    Left at 0–255 a slice ships whatever grey the scanner produced, and the
+    downscale to the song's width then blends every stroke edge further, so a
+    fine engraving arrives on the tablet as a wash. Notation is two-tone by
+    nature — ink and paper, nothing in between — so Otsu's split is exactly the
+    measurement wanted, and the points sit halfway to each end of the range from
+    it. Halfway rather than at the split itself: the ramp between them is the
+    antialiasing, and collapsing it would leave the notes jagged.
+    """
+    split = float(cv2.threshold(gray, 0, 255, cv2.THRESH_BINARY + cv2.THRESH_OTSU)[0])
+    if split < 1:
+        # A page already scanned bilevel has no interior split to find, and
+        # Otsu degenerates to 0. There is nothing between ink and paper to
+        # stretch, so leave the sliders where they are.
+        return 0, 255
+    return int(split / 2), int(split + (255 - split) / 2)
+
+
 def _gap(run: tuple[int, int], anchor: Anchor) -> int:
     """Vertical distance between an ink run and a bracket; 0 if they overlap."""
     start, end = run
@@ -387,5 +408,9 @@ def detect_page(gray: np.ndarray, skew: float | None = None) -> PageDetection:
     # would risk clipping a tempo mark or a section label above the first staff.
     left, right = content_columns(straight, anchors)
     return PageDetection(
-        skew=angle, systems=systems, cuts=cuts, content=(left, 0.0, right, 1.0)
+        skew=angle,
+        systems=systems,
+        cuts=cuts,
+        content=(left, 0.0, right, 1.0),
+        levels=ink_levels(straight),
     )
diff --git a/noteman_slicer/project.py b/noteman_slicer/project.py
index 4ef00cb..cd3d804 100644
--- a/noteman_slicer/project.py
+++ b/noteman_slicer/project.py
@@ -15,6 +15,7 @@ import hashlib
 import json
 from dataclasses import dataclass, field
 from pathlib import Path
+from statistics import median
 
 from .detect import PageDetection
 
@@ -296,7 +297,18 @@ class Project:
                     content_rect=detection.content,
                 )
             )
-        return cls(source=source, source_hash=hash_file(source), pages=pages)
+        # Levels per song, not per page: a scanner's contrast does not change
+        # between sheets, and one pair of sliders for the whole song is what a
+        # user actually wants to nudge. The median keeps a near-blank page —
+        # where the ink/paper split is guesswork — from setting them.
+        proposals = [d.levels for d in detections] or [(0, 255)]
+        levels = (
+            int(median(b for b, _ in proposals)),
+            int(median(w for _, w in proposals)),
+        )
+        return cls(
+            source=source, source_hash=hash_file(source), pages=pages, levels=levels
+        )
 
     def save(self, path: Path | None = None) -> Path:
         """Atomic write, so a crash mid-save cannot destroy the previous state."""
diff --git a/tests/test_detect.py b/tests/test_detect.py
index 58f06fd..8afc0cc 100644
--- a/tests/test_detect.py
+++ b/tests/test_detect.py
@@ -14,7 +14,12 @@ import numpy as np
 
 sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
 
-from noteman_slicer.detect import deskew, deskew_angle, detect_page  # noqa: E402
+from noteman_slicer.detect import (  # noqa: E402
+    deskew,
+    deskew_angle,
+    detect_page,
+    ink_levels,
+)
 
 W, H = 1000, 1400
 STAFF_GAP = 15  # → staff height 60, so expansion reaches 90px past a bracket
@@ -71,6 +76,15 @@ def main() -> int:
         found = deskew_angle(deskew(page, angle))
         assert abs(found + angle) <= 0.15, f"skew {angle}: got {found}"
 
+    # Levels are proposed too. A grey scan left at 0–255 ships its wash to the
+    # tablet, and the downscale to the song's width only blends it further.
+    grey = np.full((H, W), 210, np.uint8)  # paper, not white
+    grey[200:400, 100:900] = 70  # ink, not black
+    black, white = ink_levels(grey)
+    assert black < 70 < white < 210, (black, white)
+    # A page already bilevel has nothing between ink and paper to stretch.
+    assert ink_levels(_page()) == (0, 255)
+
     # A scanner's edge line runs the whole height of the sheet. Being taller
     # than every bracket it used to win each overlap and swallow the page into
     # one system — Olukainen juomukainen, where five pages of six came out as a