focus-stack

focus-stack is a free desktop tool for combining photos taken at different focus settings. It is best suited to microscope photographers and other users who want control over a focus-stacking workflow; its alignment and depth outputs are useful, but memory needs can be substantial.

Overview

The program builds an extended-depth-of-field image by selecting the sharpest source image at each pixel. That approach suits subjects whose depth exceeds what a single frame can keep in focus, a common challenge in microscope photography. Automatic alignment can resize and rotate images to bring frames into register, and users can skip or adjust alignment when it is unnecessary or unsuitable.

Alongside the composite, focus-stack can generate a depth map and a 3D preview derived from that map. These options add ways to inspect a stack, though the central job remains combining differently focused photographs.

Key features

• Alignment controls: Resizing and rotation help reconcile differences between source images. Being able to skip or adjust alignment is useful when a stack is already aligned or automatic correction is not appropriate.
• Processing controls: Denoising, consistency filtering, batch size, and thread count provide control over processing. The batch and thread settings also matter for memory consumption.
• Image formats: Input supports formats handled by OpenCV, including JPG, PNG, and TIFF. Output format is determined by the file extension, with JPG and PNG among the supported outputs.
• GPU acceleration: OpenCL acceleration can use a compatible GPU when available, and an option disables it. That gives users a choice when acceleration is unwanted or unavailable.
• Depth outputs: A depth map and a 3D preview are optional additions to the stacked image, useful for users who want more than the composite alone.

Pricing

focus-stack is free: its plan is free, with no stated usage limits. There is no free trial because the software itself is offered as a free plan. That makes it straightforward to consider for occasional or specialist use without a subscription commitment.

The trade-off is not a tiered feature set but the practical work of running desktop software. The README estimates about 100 MB of RAM per megapixel at default settings. Using one thread and a batch size of two lowers that estimate to about 50 MB per megapixel, but still calls for planning with large images or stacks.

Platforms

Desktop packages are available for Windows 10, Ubuntu 20.04, and Mac OS X, while the project’s platform coverage includes Linux, macOS, and Windows. The macOS application is unsigned and may be quarantined by the operating system, so Mac users should expect an installation caveat. Linux users building from source need OpenCV 3.0 or newer and basic build tools. The project is MIT licensed.

The releases page lists Version 1.5 and a separate prerelease called latest. An Android app from a third party uses focus-stack’s algorithm, but that is distinct from the desktop software.

Who it's for

Microscope photographers are the clearest fit, particularly when a subject spans more depth than a single photograph can capture. It can also suit other desktop users who already have a sequence of differently focused images and want alignment controls, processing options, or a depth map alongside the final image.

It is a less compelling choice for users who need a polished, low-resource workflow or want a native Android version of this project. The estimated RAM use can become a constraint as image resolution rises, and the Android connection is a third-party app rather than a desktop package for phones.

Pros and cons

• Pro — Flexible alignment: Resizing, rotation, and the option to skip or adjust alignment accommodate stacks that need different treatment.
• Pro — More than a composite: Optional depth-map and 3D-preview outputs extend the result for users who want to examine depth information.
• Pro — Useful processing controls: Denoising, consistency filtering, batch size, and thread count give users options to tune a run.
• Con — High memory estimates: The default estimate of about 100 MB per megapixel can make large images demanding; reduced settings lower but do not eliminate that concern.
• Con — macOS installation friction: The unsigned app may be quarantined by macOS.
• Con — Packages target older named releases: The README identifies packages for Windows 10, Ubuntu 20.04, and Mac OS X, rather than describing broader package coverage.

Alternatives

For more options, see Focus Stacking Software.

• Focus Stacking Online is the better fit for anyone who wants free online focus stacking or broader platform coverage including Android, iOS, and web.
• CKAN is another free, MIT-licensed option for Linux, macOS, and Windows.
• ImageFocus Alpha is aimed at owners of compatible Euromex camera models and also covers Android and iOS.
• PlaneFuse may suit users looking for a free MIT-licensed option for personal and commercial use across web, self-hosted, API, and desktop platforms.
• ChimpStackr is a free, multi-platform focus-stacking alternative under GPL-3.0.
• ForgePix is another free MIT-licensed option for Linux, macOS, and Windows.
• Open Galileo is a free Windows alternative; its maker says it will always be free and accepts voluntary donations.
• OpenFocus is worth considering if a GUI for Windows or macOS, or a CLI covering Windows, macOS, and Linux, better suits the workflow.

Verdict

Choose focus-stack if you need a free desktop focus-stacking tool with alignment controls and optional depth outputs, especially for microscope photography. Its processing controls and broad OpenCV input support are useful strengths. Look elsewhere if memory constraints, the unsigned macOS app, or the need for a more accessible workflow outweigh that control.