The photo culler that keeps up with your shutter.

Falcon is a free, open-source app for the job between the memory card and the editor: looking through thousands of frames and choosing the keepers. Open a folder, fly through RAW + JPEG bursts at the speed they were shot, check focus at 1:1, rate, flag and compare, then hand your picks to Lightroom, Capture One or the web.

I'm a photographer and a designer, and I designed Falcon for my own shoots. This page is both the project's README and a record of the design thinking behind it.

Windows 10 and 11 · Apple Silicon Macs · Download

Watch the video on YouTube.

• Why I built it
• Design principles
• Design in practice
• What Falcon is not
• The icon
• How it was made
• Download and first launch
• Requirements
• Supported files
• Keys
• Building from source
• Credits and licence

My camera, a Canon EOS R5 Mark II, shoots 30 frames a second. One second of a bird taking off is thirty photos, and a day's shoot is thousands. Looking through them should be the quick part of the job. It wasn't.

None of the photo viewers I tried could keep up with that speed. Hold the arrow key and they stall on a loading screen or a black frame, so a burst that took two seconds to shoot takes far longer to look through. Most also show a RAW file and its JPEG as two separate images, so every moment has to be judged twice.

Before building anything, I studied the viewers that already exist. They fell short in three ways: interaction design, speed with large high-resolution bursts, and working the same way on Windows and Mac. A feasibility check followed, and I decided to build a new tool.

The first prototype was a web app, built with React. It was nowhere near fast enough for culling, so the whole app was rebuilt in Rust, which runs natively and can use every processor core and the graphics card.

Six ideas shaped every decision in Falcon.

1. Speed is the product. A culling tool that makes you wait has failed at its one job. Every change is measured: time to the first photo, decode times, frame pacing. Anything that makes browsing hesitate is treated as a defect, not a nuisance.

2. The photo is sacred. Selection, hover and rejection appear around the photo as borders, glows and lifts, never as a tint over it, because you can't judge colour through a coloured overlay. Colour is managed end to end, from each photo's embedded profile to your monitor's own profile, and that includes the colours of the interface itself.

3. Culling is thinking, not clicking. Choosing between near-identical frames means looking and reflecting. Falcon never moves on for you: there is no auto-advance after a rating and no slideshow timer. An independent design review recommended auto-advance as its top change, as many culling apps do it. I turned it down, because the keystroke it saves was never the cost; breaking your concentration is. Falcon removes friction instead, with instant previews, one-key judgements and short hand travel, and you set the pace.

4. Designed for people who think visually. Photographers, like designers, think with their eyes. No feature in Falcon hides behind a keyboard shortcut alone. Every action is in the right-click menu, which also shows its key. Panels shrink to a small visible button instead of disappearing, so there is always a way back.

5. Folders, not a catalogue. There is no import step and no library database to maintain. Falcon opens the folder in front of you, and remembers your sort order and your place when you come back.

6. Quiet and consistent. The interface is a dark, flat viewing space built from one set of colours, spacing and motion rules. Motion is restrained and can be switched off. Anything that competes with your photographs is kept out.

Hold the arrow key and Falcon moves through the folder at a sustained 30 frames per second, the same rate my camera shoots. A burst plays back as motion: a wingbeat or a sprinter's stride unfolds on screen, and you stop on the exact frame you want. Settings go up to 120 frames per second, as fast as your hardware allows.

The decision behind it: never decode a 45-megapixel file just to show it for a thirtieth of a second. While you move, Falcon shows screen-sized frames it has prepared dozens of photos ahead, in the direction you are going. The moment you stop, that photo sharpens to full resolution, and the frames around it are prepared sharp too, so stepping back and forth around a moment stays instant.

Many cameras save each shot twice: a RAW file and a finished JPEG or HEIC. Falcon treats the pair as one photograph everywhere. It is one frame in the filmstrip, whichever file you opened, and ratings, flags, copying and deleting act on both files together. Compared with a viewer that shows both files, there are half as many images to look through, and your judgement belongs to the photograph rather than to one of its files.

You browse on the camera's finished image and switch to the RAW with one click to see it developed, including Fujifilm X-Trans files. The switch names the real format of the finished file, such as JPG, HEIC or PNG. When a RAW has no usable finished image, it says Preview, because that is what you are looking at.

Double-click one photo in a folder of ten thousand and Falcon shows that photo first, before it has finished reading the folder. You can zoom and pan straight away while the filmstrip and the rest of the folder fill in behind it. In a test reopening an 11,831-file RAW + JPEG folder, the 45-megapixel photo was on screen about 0.7 seconds after launch.

To make that possible, Falcon identifies each file from its first 32 bytes and pairs RAW and JPEG files by name without opening the RAWs. The photo you are looking at always comes first, and all other preparation gives way to it.

A 48-megapixel iPhone HEIC is made of dozens of compressed tiles, and a folder of them can bring a computer to its knees. On Windows, Falcon reads the HEIC file itself and sends each tile to the graphics card's own video decoder, then assembles the tiles and converts the colour on the graphics card too.

On my NVIDIA desktop, holding the arrow key for 12 seconds through 100 iPhone HEICs prepared all 100 frames, where Windows' own software decoding prepared 11. A sharp frame arrived in a third of a second instead of 0.84 seconds. The fast path isn't limited to NVIDIA: it uses whatever HEVC video decoder the graphics driver provides, and Falcon checks folder by folder that it is really serving your photos before relying on it. On a Mac, HEIC opens natively through Apple's own image framework.

Press C, or drag a filmstrip thumbnail upward, to put two frames side by side. Zoom and pan stay linked across both halves, so you inspect the same eye in both at once. Pin the frame you like, then step through challengers against it. Your rating goes to whichever half you are focused on.

• Focus check in one click. Click a photo to see true 1:1 at that point. The badge reads Focus 1:1 only when you are really looking at full-resolution pixels.
• One-key judgements. Rate, pick and reject with single keys, and undo anything, including deletes and moves. Select many photos and the menu says exactly what a key will touch ("Reject 40").
• Review panel. Filter by picks, rejects or rated shots, with a larger preview on hover.
• Hand-off. Copy picks as untouched originals, move rejects aside, or export JPG or PNG copies, resized, converted to sRGB and watermarked.
• Immersive mode. Press F and the interface disappears. Move to a corner and the rating controls appear.
• Safe with your originals. Falcon never re-encodes your photos. Deletes go to the Recycle Bin or Trash with Undo, and your ratings are saved safely beside the photos.
• Ready for location work. Efficiency mode stretches a laptop's battery, and photos that live only in OneDrive aren't downloaded just because you scrolled past them.
• At home on a Mac. The native menu bar and full screen, trackpad pinch to zoom, and Falcon as Finder's default viewer.

Falcon is built for one workflow, viewing and culling, and deliberately leaves the rest to other tools.

• Not a photo editor. Crop, exposure and white balance belong in your editor. Rotation is the only change Falcon can make to a file, and only when you choose to apply it.
• Not a catalogue. There is no import, no cross-folder library and no keyword or face search.
• A narrow export. Copies are JPG or PNG in sRGB, for sharing. There is no print module and no upload.
• SDR only. There is no HDR display output.
• No screen-reader support yet.

The icon grew out of my own abstract drawings. I set the rules first: one to three simple shapes, recognisable at 16 pixels in a taskbar or Dock, and a palette of blues. I took passages from my own pencil drawings, reworked them into clean shapes and refined the mark through several revisions in Figma until it held up at taskbar size.

I'm the designer, and AI agents were the engineers: mainly Anthropic's Claude, and later OpenAI's Codex, working under my direction. I made every decision about how Falcon looks, how it behaves and what it includes. I judged each build on real shoots and fed back with annotated screenshots and logs from my own laptop and a MacBook tester.

The work ran in rounds: a written plan, the build, independent reviews by other agents, then verification. Riskier changes were cross-checked between Claude and Codex. Speed claims need a measurement, and bug fixes start from a test that fails. I reviewed the design against Nielsen's and Norman's usability principles, and against my own rules, such as "culling is thinking" above.

The private development history holds about 680 commits, and the test suite runs more than 1,700 automated tests.

Download Falcon from Releases. Each release includes the packages, their checksums and the matching source. The packages contain the app together with its licence and rebuild documents; keep those with the app.

Falcon is free, so it doesn't use paid code signing. Windows builds are unsigned, and Mac builds have a free ad-hoc signature without Apple notarization, so your system asks you to confirm the first launch:

• Windows: extract the package to the folder where you want to keep Falcon and open Falcon.exe. If SmartScreen blocks it, choose More info → Run anyway. To open photos with Falcon from Explorer, use Settings → File associations → Update.
• macOS: move Falcon.app to Applications and open it. If macOS blocks it, go to System Settings → Privacy & Security, choose Open Anyway for Falcon and confirm. macOS remembers this choice. See Apple's instructions.

Keep your system's security checks switched on; work computers may not allow these exceptions. The checksum confirms the download is intact, but it is not a publisher's signature.

• Windows 10 or 11, 64-bit. One portable app with no installer. Integrated graphics work. NVIDIA acceleration is used automatically when a compatible nvJPEG runtime is installed; CPU decoding works without it. HEIC photos need Microsoft's HEIF Image Extensions.
• macOS 12 or later on Apple Silicon. HEIC works out of the box.

RAW decoding uses rawler, so support can vary by camera model.

Almost every key can be changed in Settings, and every action is also in the right-click menu.

Full instructions are in BUILDING.md. In short:

cd falcon
cargo build --locked --release --bin falcon
cargo test --locked --workspace

rustup installs the pinned Rust toolchain (1.96.0) automatically. Windows builds also need the Visual Studio C++ Build Tools and the Windows SDK; Mac builds need Xcode.

Under the hood, the interface is built with Slint on wgpu: DirectX 12 or Vulkan on Windows, Metal on Mac. Decoding, colour and graphics work live in Falcon's own crates. NVIDIA nvJPEG and DirectX hardware HEVC decoding are optional accelerators detected at runtime, with fallbacks that need no NVIDIA software; CUDA and HEVC software decoders are not bundled. The repository includes modified copies of the winit window library and zune-jpeg decoder, which the build requires. Private camera test files are not included, and the tests say when they skip those checks.

The detailed technical guide and architecture diagrams are in logic.md.

Designed by Hancheng Wu. Developed with assistance from Claude and Codex. Copyright 2026 Hancheng Wu and contributors.

Falcon's original project material is licensed under Apache-2.0. Dependencies keep their own terms; see NOTICE, THIRD-PARTY-NOTICES.txt and the corresponding source materials. RAW development uses rawler under LGPL-2.1, and REBUILDING.md explains how to modify that library and rebuild the app. The Slint badge above is part of the chosen toolkit attribution route. This software is based in part on the work of the Independent JPEG Group.

Issues and pull requests are welcome; see CONTRIBUTING.md. This repository contains reviewed source snapshots. Private development history, personal photographs and internal conversation records are not published.