WINDER

Splitting scans

The heart of Winder is the splitter. This page explains what it does and every knob you can turn.

Why scans need splitting

A half-frame camera exposes two 18×24mm shots inside one 24×36mm frame. Labs scan the full frame, so every file you get back holds two photos separated by a strip of unexposed film — a black bar a couple of millimetres wide, not a thin line.

How detection works

Winder walks the luminance profile across the middle of the scan looking for that dark valley:

  1. It samples brightness column by column in the central ±18% of the scan (the divider is always near the middle; a dark subject at the edge can't fool it).
  2. It looks for a contiguous run of columns that are markedly darker than the median — the valley.
  3. The valley's center becomes the proposed cut; its width becomes the bar width. Both are shown in the review screen.

Rotated scans are handled too: Winder scores both axes and splits along the stronger valley, so it doesn't matter whether your lab scanned the strip horizontally or vertically.

When detection fails

Very dark frames (night shots, heavy underexposure) can hide the bar. In that case Winder falls back to a center cut using the fallback divider width from Settings, and tells you so in the review screen — nothing is cut without you seeing it first.

The review screen

  • Drag the bar to move the cut. The two half previews update live.
  • Rotate either half in 90° steps.
  • Keep both / left / right — sometimes one half is a lens cap test.
  • Discard scans that shouldn't be imported at all.
  • Auto-straighten (Pro) suggests the upright orientation for every frame in the batch.

Settings that affect splitting

| Setting | Default | What it does | | --- | --- | --- | | Scan size | 3130 × 2075 px | The pixel size of a full 35mm scan from your lab | | Divider fallback width | 140 px | Bar width assumed when detection fails | | Trim frame edges | On | Shaves the dark rebate off each frame after the cut | | JPEG quality | 95 | Output quality for the two saved frames |

All of it lives in Settings → Film & scanning.

Provenance

Every split frame remembers where it came from. Its sidecar records the original scan's filename, which half it was, the cut position and the rotation applied — so no cut is ever a mystery later.