Compositor: An Open-Source Photoshop Alternative for macOS
Compositor is a free, open-source Mac image editor with layers, masks, adjustments, retouching, and a native Swift workflow.
Compositor: An Open-Source Photoshop Alternative for macOS
Professional image editing on the Mac often comes with an uncomfortable trade-off: Photoshop is powerful but expensive, while free alternatives such as GIMP can feel unfamiliar enough to interrupt an established workflow. Compositor takes a different approach—a free, open-source image editor designed specifically around Photoshop-style compositing and post-processing.
The project is aimed at creators who want a native Mac application with familiar tools, non-destructive editing, and the freedom to inspect or modify the source code. The repository is primarily written in Swift, with 96.5% of the codebase in Swift and a small amount of C.
A workflow built around compositing
Compositor is not positioned as a lightweight image viewer or a basic paint program. Its feature set is centered on building pixel-perfect final images from multiple elements, which makes layers, masks, transformations, selections, and adjustments central to the experience.
The editor supports multiple projects in tabs and uses Photoshop-style keyboard shortcuts throughout. That emphasis on familiar interaction is important: the project’s motivation is not simply to provide free image editing, but to help users remain in an established creative flow without paying for a subscription.
Layers, masks, and adjustments
The layer system includes the building blocks expected in a serious compositing application:
- Layers and folders with blend modes and opacity controls
- Drag-and-drop reordering and nesting
- Inline renaming and Option-drag duplication
- Moving layers between open projects
- Merge Down, Merge Layers, and Merge Group using
⌘E - Clipping masks and folder masks
- Layer masks that can be painted, filled, inverted, blurred, and feathered
- Linked or independent mask transformations
Compositor also supports adjustment layers for non-destructive editing. Available adjustments include Hue/Saturation, Levels, Curves, Exposure, Gradient Map, and Grain. This makes it possible to refine an image without permanently changing the original layer pixels.
Non-destructive transformations
Transformations are designed to preserve source quality. Images retain their full resolution even when scaled down, and users can move, scale, rotate, and flip content non-destructively.
The transform workflow includes:
- Free distortion by dragging handles with
⌘ Shiftto constrain distortion to an axis- Transforming multiple layers or an entire folder together
- Snapping to canvas edges, layer edges, and centers
- Guides for alignment
- Exact position, size, scale, and angle values
- Arrow-key stepping for precise adjustments
- Horizontal and vertical layer or canvas flipping
These capabilities are especially useful for UI mockups, photo composites, promotional graphics, and any project where alignment matters as much as visual appearance.
Selections and content-aware editing
The selection toolkit covers both geometric and freeform workflows. It includes Rectangle and Ellipse Marquee tools, Freehand and Polygonal Lasso tools, and a Magic Wand.
Selections can be added to or subtracted from, moved independently, or used to move and duplicate pixels. A layer’s pixels or a mask can also be loaded directly as a selection, which is useful when building precise masks from existing artwork.
One notable feature is Content-Aware Fill, including the ability to extend an image beyond its original edges. That can help remove distractions, fill empty areas, or expand a composition without immediately reaching for an external tool.
Painting, retouching, and filters
For direct editing, Compositor includes a configurable brush with size, hardness, and opacity controls. Holding Shift creates straight lines, making the brush useful for both freehand work and controlled marks.
Retouching tools include:
- Spot Healing Brush with content-aware processing
- Clone Stamp with aligned and non-aligned modes
- Sampling from the current layer or all visible layers
- Blur applied to pixels or masks
- Gradient and Shape tools
- Eyedropper and full color picker
The adjustment and filter collection includes Levels with Auto, Curves, Hue/Saturation, Exposure, Gradient Map, Grain, Invert, Gaussian Blur, Motion Blur, Add Noise, Lens Correction, and Remove Background. Gaussian and Motion Blur can spread beyond a layer’s edges, which is useful for natural-looking effects on isolated objects.
Live previews are available and can be limited to the current selection, allowing users to evaluate an effect before committing it across an entire layer.
Canvas and file support
Compositor imports JPEG, PNG, HEIC, and TIFF files. It also supports dropped screenshots and images copied from other applications, which fits naturally into a Mac-based workflow.
Canvas tools include cropping with snapping, symmetric cropping with Option, Canvas Size, and Image Size. When zoomed out, the application uses high-quality downsampling; when zoomed in, it provides a pixel grid for detailed pixel-level work.
Export currently includes JPEG with a live preview through ⇧⌥⌘S, along with a Copy Merged command for copying the visible composite rather than a single layer.
Building from source
Compositor requires:
- macOS 26
- Xcode 26
To build the application, clone the repository, open the project, and run the Compositor scheme:
git clone https://github.com/robbietilton/Compositor.git
cd Compositor
open Compositor.xcodeproj
In Xcode, select the Compositor scheme and run the project. Because the project is open source, developers can add, remove, or adapt features to match their own workflows.
Release packaging and notarization
The repository includes scripts/release.sh for producing a distributable release. The script builds a Release version, signs it with a Developer ID certificate, submits it for notarization, staples the notarization result, and packages the application as:
dist/Compositor-<version>.dmg
Release builds require the following dependencies and credentials outside the repository:
- A Developer ID Application certificate in the login keychain
- Notarization credentials stored with
xcrun notarytool, using thecompositor-notaryprofile create-dmg, installable with Homebrew:
brew install create-dmg
This setup makes the project useful not only as an end-user application but also as a reference for developers interested in a complete macOS distribution pipeline involving code signing and notarization.
Project status and license
The repository’s latest listed release is Compositor 1.0.4, published on September 18, 2026. It has 1.4k stars, 149 forks, and 9 watchers, with five releases reported on GitHub. The project has two listed contributors: Robbie Tilton and Claude.
Compositor is distributed under the MIT License, making it permissive for inspection, modification, and reuse. For Mac users looking for a familiar, subscription-free editor—and for developers interested in a focused native Swift application—Compositor is a compelling open-source project to explore.