the film look from Relay. now open source.
Every photo shot in Relay develops through one filter. It was measured against real film, it runs in five Metal kernels, and the whole thing is now free to read, build, and ship.
Drag the handle. Left is straight off the sensor, right is Relay.
Same filter, every scene.
No presets and no strength slider in the app. The filter reads each photo and adapts its exposure on its own, so a dim taco run and a noon surf line both come out looking like they belong to the same roll.
How it works.
Internally the filter is called Marenn 400. It is not a LUT. It is a five pass Metal compute pipeline that was tuned by measuring real film scans, aligning them to digital captures, and fitting each stage until the difference dropped to a few dE. Warm, never teal.
Tone and color
A seven knot spline tone curve, warm shadow and highlight tints, and a dedicated blue sky treatment that saturates, deepens, and hue shifts skies the way negative film renders them.
Highlight softening
Bright regions get a gentle ring blur and a touch of bloom, so highlights roll off like film instead of clipping like a phone photo.
Halation source
Extracts everything above a luminance threshold and tints it toward the warm orange glow that halation has on real stock.
Halation spread
Two separable Gaussian passes at half resolution spread that glow outward, sized relative to the photo so it scales from thumbnails to full captures.
Optics and grain
The final pass screens the halation back in, then models the lens: anisotropic edge defocus, chromatic aberration that grows toward the corners, a soft vignette, and two octave value noise grain that lives mostly in the shadows. Exposure is scene adaptive, driven by a luminance histogram of the actual photo, so the filter meets every shot where it is.
Take it apart.
The repo has the shipped Swift and Metal source, exactly what runs in the app, plus a macOS command line harness that compiles the shader straight out of the filter file and runs it on any image. Every constant is the real shipped value.
It is licensed under GPL-3.0. Use it, learn from it, build on it, and keep what you make open too. The Relay name and logo stay ours.
clone, build the harness, develop a photo $ git clone github.com/SMGStudiosLLC/Mareen-400 $ swiftc -O Tools/marenn_cli.swift -o marenn $ ./marenn MarennFilter.swift beach.jpg out.png