nomacs

nomacs is a free, open-source image viewer that runs on Windows, macOS and Linux from one code base. It looks like a conventional viewer at first - a canvas, a thumbnail strip, a menu bar - but two features separate it from the crowd. The first is image synchronisation: several nomacs windows can be locked together so that zooming, panning and rotating one picture applies the same transform to the others, which is invaluable when comparing focus, exposure or two versions of an edit. The second is a metadata-first design: EXIF, IPTC and XMP values have their own dockable panel, and the thumbnail strip can be sorted and filtered by them.

What it does

nomacs opens the common raster formats, animated GIF and WebP, SVG, camera RAW through LibRaw, and multi-page TIFF and PDF-like containers. Editing is modest but practical: crop, resize, rotate, flip, brightness, contrast, gamma, hue and saturation, plus a threshold and a pseudo-colour mode that maps luminance to a false-colour ramp for inspection work. A plugin interface adds panorama stitching, image montage, a painter, a batch tool and a page extractor, and the plugin set is loaded at startup from a single folder.

The workflow

Open a folder, use the thumbnail strip to find the frames that matter, and then open two or three of them in separate windows. Enable synchronisation and every zoom, pan and rotation is mirrored across all of them, so you can compare sharpness at 100 percent or check whether a dust spot moved between frames. Switch the metadata panel on to read capture settings, then apply a quick crop or a brightness nudge and save to a new name. For colour-critical inspection, the pseudo-colour map turns subtle gradients into visible steps.

Practical settings and limits

The viewer caches thumbnails per folder, so first visits to a large directory can pause while the strip fills. Editing is destructive in the sense that changes are written into the saved file, and there is no history or layer stack, so work on copies when the originals matter. Advanced format support depends on the bundled libraries and on the platform build, and the plugin collection has to be installed separately on Windows. Comparison work is limited to a handful of synchronised windows before screen space runs out.

Who should choose something else

Users who want batch conversion, a catalogue database or layer-based editing will need a different primary tool, and anyone who only opens a picture now and then will find the built-in viewer sufficient. nomacs is the right choice when the job is looking closely - comparing frames, reading metadata and inspecting tonal detail across several images at once.