Three things a first session trips over.
The editor opened at an arbitrary zoom. show_page does fit the page, but
it runs before the window has been laid out, when the viewport is still
its default size; redo it once when the real size arrives.
The bundle was named after the PDF, which is whatever the download was
called. Take the song's title instead — unsafe characters dropped, then
whitespace collapsed to dashes. Accented letters stay, since ä and ö are
not a filesystem's problem, but a leading dot would hide the file.
And the selected slice was drawn as an outline whose top and bottom edges
run under the cut lines painted over them, leaving two thin verticals in
the margins and no way to tell what was selected. Wash the slice, as the
discard and engraved states already do, and keep the outline for the trim
anomalies it exists to show.
Levels shipped at 0–255 unless someone moved the sliders, and Bicycle
Race showed what that costs. Its ink is grey, not black — a scanned
engraving, ink at 2–95, paper at 163–255 — and with alpha = 255 − luminance
that greyness becomes transparency. No pixel in the exported bundle was
even fully opaque, and the downscale to the song's width blended every
stroke edge further. Nothing downstream can rescue it.
So detection proposes levels too, like it proposes cuts and skew.
Notation is two-tone, which makes Otsu's split the measurement wanted;
the points sit halfway from it to each end of the range, so the ramp
between them survives as antialiasing rather than going jagged. A page
already scanned bilevel has no interior split — Otsu degenerates to 0 —
and is left alone. Per page, with the median becoming the song's, so a
near-blank page cannot set them.
A first user hit a wall at the door: the README still said "design only,
no code yet", and nothing anywhere said how to drive the editor.
docs/guide.md walks one PDF to one bundle — install, the five per-page
decisions, markers and jump targets, the title block, export — with a
mouse/key table and the failures that actually happen. The README's stale
status and installation lines go with it.
Esa Kataja