NegPy marcinz606

film-photography image-processing photography

Use this command to install NegPy:

winget install --id=marcinz606.NegPy -e

Tool for processing film negatives.

NegPy

NegPy is a tool for processing film negatives. I built it because I wanted something made specifically for film scans that goes beyond a simple inversion tool. It simulates how film and photographic paper work but also throws in some lab-scanner conveniences.

It is built with Python, running natively on Linux, macOS, and Windows.

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User Guide

Click here to read the USER_GUIDE.md — A complete walkthrough of the NegPy workflow, features, and controls.

Features

Conversion & Film Science

No Camera Profiles: No camera profiles, no border colour-picking. Math neutralizes the orange mask from channel sensitometry.
Film Physics: Models the H&D Characteristic Curve in density space — an asymmetric toe-linear-shoulder response with independent softplus toe/shoulder knees and ISO-R paper grades — instead of a linear inversion.
Smart Auto Conversion: Per-frame Auto Density and Auto Grade meter each negative for sensible brightness/contrast — usable out of the box, easy to fine-tune.
Darkroom Paper Profiles: Per-paper curve shaping (tone, per-channel gamma, base tint) mapped from Ilford/Kodak/Foma/Fuji datasheets, selectable per roll.
Positive/Slide Support: Dedicated E-6 mode with optional normalization to save expired or faded film.

Capture & Input

Camera Scanning: Capture negatives with a tethered camera straight into NegPy — a single RAW, or automated red/green/blue narrowband triplets driven by an RGB Scanlight that feed the RGB Scan merge. macOS/Linux, optional dependency. Camera Scanning guide
Scanner Support: Direct control of SANE-compatible film scanners — Plusteks, Nikon Coolscans and others
RGB Scan (Trichromatic Capture): Merge three narrowband red/green/blue exposures of one negative into a single low-noise colour scan, with automatic sub-pixel alignment to kill fringing.
Flat-Field Correction: Correct illumination falloff / vignetting from your light source or scanner via a reference scan of the bare light. Named profiles, toggle per image.
File Support: Standard RAWs/TIFFs plus specialized formats like Kodak Pakon scanner raw files.

Editing

Dodge & Burn: Darkroom-style local lighten/darken with freehand polygon masks — each with its own EV strength and feather. GPU-accelerated with bit-for-bit CPU parity.
Dust Removal: Automatic and manual healing with grain synthesis — clean scans that don't look plastic.
Batch Normalization: Bounds analysis across all loaded files, averaged and applied to the roll.
GPU Acceleration: Real-time processing and export rendering via Vulkan/Metal.

Colour & Output

Colour Management: Full ICC workflow — auto monitor-profile detection (Linux/macOS/Windows), soft proofing including paper/printer profiles, per-image input/output profiles.
Print Ready: Export built for printing — border controls, ICC soft-proofing, dynamic filename templating, export presets (save + one-click), and contact sheets. Formats: JPEG, TIFF, PNG, WebP, JPEG XL.
Flat / Digital-Intermediate Export: Flat, neutral, wide-gamut 16-bit TIFF master for Lightroom/Darktable/Photoshop, mapping camera RAWs to ProPhoto via the camera's own matrix.

Workflow & Data

Non-destructive: Original files never touched; edits stored as recipes.
Database: Edits in a local SQLite db keyed by file hash — move or rename files without losing work.
Persistent Undo/Redo & History: Up to 100 edits per file. History panel lists every step — jump to any state, branch, or export an earlier version. Survives restarts.
Metadata & Gear Library: Archival metadata for the original analog capture — manage a library of cameras, lenses, and film stocks, apply gear presets per frame, and write real camera/lens/ISO EXIF (plus XMP scan tags) into exports so Lightroom shows your film gear. see the guide
Keyboard Shortcuts: see here

How it works

Read about the math and the pipeline here

Getting Started

Download

Grab the latest release for your OS from the Releases Page.

Linux

I provide an .AppImage. Make it executable using chmod +x and It should just work.

Scanner support requires SANE to be installed on your system:

sudo apt install libsane        # Debian/Ubuntu
sudo pacman -S sane             # Arch

Or your distro's equivalent. The app launches fine without so you can ignore that if you don't plan to use a scanner.

Camera scanning support (optional) uses python-gphoto2 for tethered capture, and may need the system libgphoto2 installed:

sudo pacman -S libgphoto2        # Arch

Or look up your distro's equivalent package.

Unsigned Software Warning

Since this is a free hobby project, I don't pay Apple or Microsoft ransom for their developer certificates. You'll get a scary warning the first time you run it.

macOS:

Double click .dmg file & drag the app to /Applications.
Open Terminal and run: xattr -cr /Applications/NegPy.app (this gets rid of the warning).
Launch it.

If you build the DMG yourself on macOS, set NEGPY_MACOS_ARCH=x86_64 for an Intel build or NEGPY_MACOS_ARCH=arm64 for Apple Silicon.

Scanner support requires SANE via Homebrew:

brew install sane-backends

The app launches fine without so you can ignore that if you don't plan to use a scanner.

Camera scanning support (optional) uses python-gphoto2, and may need libgphoto2 from Homebrew:

brew install libgphoto2

Windows:

Run the installer (ignore the warnings)
Start the app and click through the warnings.

Scanner and camera scanning are not available on Windows. Both rely on Unix-first free-software libraries - SANE for scanners, libgphoto2 for cameras, that just don't build there. It's not really their fault: the open source world spent decades writing generic, vendor-neutral drivers for hundreds of devices, while Windows stuck with closed per-vendor blobs and never grew an equivalent. So the free, open stack NegPy leans on has nowhere to stand on Windows.

Good news: you can install Linux on pretty much any Windows machine. 🐧

You can also clone the repo and build it yourself, instruction here: CONTRIBUTING.md

Data Location

Everything lives in your Documents/NegPy folder:

edits.db: Your edits.
settings.db: Global settings like last used export settings or preview size.
cache/: Thumbnails (safe to delete).
export/: Default export location.
icc/: Drop your paper/printer profiles here.
override.toml: Startup overrides — see Troubleshooting / override.toml below.

Troubleshooting

If NegPy crashes on startup or has rendering issues, edit Documents/NegPy/override.toml. It is created automatically on first run with sensible defaults for your OS.

[rendering]
# Options: "auto", "vulkan" (Linux/Win), "dx12" (Win), "metal" (macOS), "cpu"
backend = "vulkan"

[display]
# Qt scene-graph backend. Options: "auto", "vulkan", "d3d12", "metal", "opengl", "software"
qt_rhi_backend = "auto"

# Window system plugin (Linux only). Options: "auto", "xcb", "wayland"
qt_platform = "auto"

[performance]
# Cap GPU texture size in pixels — useful on low-VRAM cards. "auto" = no limit.
max_texture_size = "auto"

# Force HQ preview on/off. Uncomment to override saved preference.
# force_hq_preview = false

# Preview cache size — keeps recently-viewed photos in memory for instant navigation.
# Lower these on low-RAM machines. Uncomment to override defaults (~1.2 GB / 8 photos).
# preview_cache_max_bytes = 1200000000
# preview_cache_max_entries = 8

[logging]
# "debug", "info", "warning", "error"
level = "info"

Setting backend = "cpu" disables GPU acceleration entirely — useful if the GPU backend crashes on your hardware.

Roadmap

Things I want to add later: ROADMAP.md

Changelog:

CHANGELOG.md

For Developers

Check CONTRIBUTING.md for details.

License

Copyleft under GPL-3.

Support

If you like this tool, maybe buy me a roll of film so I have more test data :)