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SwiftInvert app icon

SwiftInvert

A native macOS film-negative converter — a Swift + SwiftUI + Metal rewrite of NegPy's C-41 conversion, no Python at runtime. Browse a folder of camera-scanned negatives, invert with NegPy-quality auto-exposure metering, refine with darkroom-style controls, and batch-export.

SwiftInvert converting a C-41 negative

Build & run

brew install libraw    # build-time only — the packaged app bundles LibRaw
./build.sh && open dist/SwiftInvert.app

Or make install to build and copy it to /Applications. The bundle is self-contained (the LibRaw dylibs are copied into it with rewritten load paths), so the built app runs on Macs without Homebrew and survives brew upgrades; Homebrew is needed only to compile. Requires macOS 14+ and a Swift 6 toolchain — Command Line Tools are enough, no Xcode; Metal shaders compile at runtime.

Features

  • Folder-tree library with film-strip previews; multi-select batch export (JPEG/TIFF, sRGB by default) with progress and cancel
  • C-41 inversion with automatic exposure and contrast metering, plus a live histogram with draggable white/black-point handles
  • Darkroom print controls (brightness, grade, toe/shoulder, True Black) and regional tone controls (shadows/highlights and their contrasts)
  • Color tools: temp/tint, per-band color grading, a chroma-gated Color Mixer (R/Y/G/B hue + saturation that never moves neutrals), vibrance/saturation
  • Crop, rotate/flip, live straighten with composition guides; per-image undo/redo history; copy/paste adjustments; HQ full-resolution preview
  • Darkroom read-outs: a spot densitometer (hover → print density + zone, with a zone strip) and a negative-character diagnostic (flat/normal/ contrasty vs the paper grade's expectation)

Development

swift run -c release SwiftInvert   # run from source (debug decode is ~10x slower)
make test                   # parity tests against NegPy-dumped fixtures (not bare `swift test`)
.build/release/negcli       # headless pipeline driver (decode/thumb/render/bench/meter)

Architecture

  • NegativeKit — pure Swift port of NegPy's conversion kernel: log-density analysis, auto-exposure metering, print-curve parameter derivation. Ported from negpy/features/exposure/{normalization,logic,models}.py.
  • MetalRenderKit — the per-pixel render chain (normalization → H&D print curve → color pop → ProPhoto ROMM encode → histogram), ported from NegPy's WGSL shaders.
  • RawDecodeKit — LibRaw wrapper matching NegPy's rawpy decode parameters (linear sensor-native decode, unity WB, EXIF orientation baked after).
  • SwiftInvert — the SwiftUI app. negcli — headless CLI for verification.

Parity fixtures

Tests/Fixtures/ is dumped from the NegPy reference implementation by scripts/dump_fixtures.py (run inside NegPy's environment; see the script docstring). Swift tests verify each stage boundary against them.

License

SwiftInvert is licensed under the GNU General Public License v3.0. LibRaw is used under its LGPL-2.1 option via dynamic linking (LGPL-2.1 §3 permits GPL conversion, making it GPL-3.0-compatible).