Rembrandt: free open-source Lightroom alternative with on-device AI hits macOS, Windows and Linux

A new free photo editor named Rembrandt has surfaced on Hacker News via a Show HN post pointing to its GitHub repository, pitched as an open-source alternative to Adobe Lightroom that runs entirely on the user's own hardware. According to the project's page, the app covers macOS (Apple silicon and Intel), Windows (x64 and ARM) and Linux (x86_64 and arm64), is licensed under the GPL v3.0 or later, and needs no account, subscription or online service for its core features.

What it does

The feature list targets Lightroom's everyday workflow: a library with albums, ratings, flags, keywords, virtual copies and search, alongside non-destructive RAW development for files from more than 1,000 cameras, with tone, colour, curves, grading, dehaze and detail controls processed on the GPU. Masking includes brushes, gradients, colour and tone ranges, plus AI-generated subject, background, object and depth selections. HDR, panorama and focus-stack merges each output a RAW-like DNG, and lens corrections draw on 1,500 profiles from the Lensfun database as well as camera-embedded profiles from Fujifilm and Sony RAWs. Batch tools cover copying edits across hundreds of photos, bulk export, and folder-watching rules that apply presets to new images as they arrive.

The AI runs on your machine

The headline AI features are local. Super Resolution upscales images 2× or 4×, AI Denoise converts high-ISO shots into a new DNG while keeping existing edits, and a Refocus tool tries to recover detail from heavily defocused pictures using regularised deconvolution on the GPU. Under the hood, subject, depth and object models come from MediaPipe, upscaling builds on Real-ESRGAN and denoising on KAIR and FFDNet; the project states nothing is uploaded. There is also a text-command bar where typing something like "shadows +25" moves the corresponding sliders, implemented as a local vocabulary rather than a large language model, according to the developer. Heavy jobs run in small GPU slices that pause while you edit, and the queue survives restarts.

How it is built

The editing engine and AI models run as JavaScript with WebGL2 and WebGPU shaders inside a small Rust desktop app built on Tauri, while RAW files are decoded by LibRaw compiled to WebAssembly. The pipeline follows darktable's scene-referred approach, in which adjustments operate on linear light before a tone curve renders the result, but the code is described as an independent implementation of published methods rather than a port. Releases are built through GitHub Actions with published SHA-256 checksums and signed build provenance. Binaries are not code-signed yet, so macOS and Windows users have to click through security warnings on first launch. Beyond the desktop app, a server mode on Linux and macOS serves the photos in a chosen folder to any browser, optionally reachable from other devices on the local network.

Portability instead of lock-in

Edits are written as standard XMP sidecar files next to each photo; the originals are never modified, and Lightroom, darktable and other tools can read the same data. Importers cover Lightroom Classic catalogs, including edits, keywords, labels and virtual copies, plus Google Photos, Google Drive, Dropbox and OneDrive. The only feature that requires an account or payment is an optional cloud sync service. The project's own comparison is candid about the gaps: there are no Print, Book, Slideshow, Web or Map modules, no face recognition, no Adobe camera profiles, no tethered capture and no plugin ecosystem, and the developer concedes that darktable and RawTherapee remain the deeper tools for fine-grained control.

Why it matters

Photography is one of the fields where subscription software and catalog lock-in bite hardest, since years of edits end up living in a proprietary database. A GPL-licensed, GPU-accelerated RAW editor with AI masking, denoising and upscaling that runs offline, writes open XMP metadata and can ingest existing Lightroom catalogs removes most of the practical barriers to switching. It is also a notable example of local AI components being composed into a polished cross-platform desktop app through web-tech rendering and a thin Rust shell. The open question is whether a project whose only revenue hook is optional sync can sustain long-term development; for now, Rembrandt stands as one of the more complete free, inspectable and exit-friendly Lightroom substitutes available.