PureRef vs Kuadro vs refern: Reference Viewer Comparison (2026)

By refern. Last updated: June 2026.

The short answer: Kuadro is a free, zero-install floating-window viewer for Windows that has not had a confirmed update since 2018. PureRef is a free canvas-based reference board with no library or search. refern combines the canvas use case both tools share with a full searchable library, hierarchical tags, and active macOS and Linux support. The tradeoff is cost: Kuadro and PureRef are free; refern costs $30 one-time after a 30-day free trial.

If you searched "pureref vs kuadro" and want to know which tool to use (or whether there is a third option worth considering), read on.

Quick verdict

What is refern?

refern is a desktop reference manager for artists that combines Eagle-style organization with a PureRef-style infinite canvas and an Obsidian-style relationship graph. It costs $30 one time, runs on Windows, macOS, and Linux, and does not copy your files.

refern indexes a normal folder you own, storing a SQLite search index and thumbnails alongside your originals without duplicating them. It launched in June 2026 with a 30-day free trial and a $30 one-time license that covers up to three devices and includes commercial use.

What is Kuadro?

Kuadro is a free, portable floating-window reference viewer for Windows, built by Luiz Kruel, a technical artist at Rockstar Games, under the Kruel Games indie label. First released January 16, 2015, it lets artists open individual reference images as separate borderless always-on-top windows, pin them over Photoshop or ZBrush, set adjustable opacity, and pass mouse events through for paint-under / tracing workflows. [Source: cgchannel.com launch coverage; kruelgames.com product page]

Kuadro's design philosophy is deliberate minimalism: it does one thing (floating reference windows) and stays out of your way. It requires no installation and runs from a single .exe on a USB drive or cloud folder. Layout presets save as .ref files using relative paths, so they survive moving to a different drive. [Source: kruelgames.com product page]

Kuadro genuinely wins on simplicity and cost. For a Windows artist who wants a few floating references while they paint and nothing else, it is hard to argue against free and zero-setup.

The significant caveats: the macOS version (v0.9.5 on Gumroad) is officially described as unsupported by the developer. [Source: luizkruel.gumroad.com/l/kuadro_osx] There is no Linux version. And development has been very quiet: the last publicly announced release was v0.9.5 in August 2018, with a small Windows bug-fix build in December 2018. A user comment on AlternativeTo from April 2022 references a v0.11, but no corresponding public announcement was found. [Source: alternativeto.net/software/kuadro]

What is PureRef?

PureRef is a unified-canvas reference board made by Idyllic Pixel AB (Viktor and Natascha, Stockholm). First released in 2013, it is the dominant tool in professional game and concept art pipelines, described as "free and basically universal in professional game development." Artists drag images onto a free infinite canvas, pin it on top of their painting or modeling app, and use click-through mode to eyedrop colors directly from references.

PureRef 2.0 (May 2024) and 2.1 (January 2026) added meaningful features: grouping with hierarchy, shapes, grid snapping, rich-text annotations, and batch image processing. PureRef runs on Windows, macOS, and Linux.

PureRef genuinely wins on free personal use, industry trust, and the quality of its always-on-top overlay. Its "pin above a specific application" mode (added in v2.0) is excellent for artists who need references visible inside ZBrush or Blender without covering other monitors.

The significant caveat: PureRef has no library, no search, no tags, and no metadata of any kind. Every image lives inside a single .pur binary file per board. There is no cross-project "all my references" view, no way to find an image by color or keyword, and no persistent metadata that survives outside a board. [Source: pureref.com/handbook/features/]

Organization and library

Kuadro

Kuadro has no library, no folder browser, no tagging, and no search. Opening a reference means navigating to it through your OS file manager each session. Users who asked for categories, collections, or search on the Polycount thread never received those features. [Source: polycount.com/discussion/146446/] If your reference collection has grown beyond a handful of frequently-used images, Kuadro will not help you find anything.

Web images opened by URL are not stored locally; users reported needing to re-download them each session because Kuadro only stores the URL, not the file. [Source: polycount.com/discussion/146446/]

PureRef

PureRef also has no library or cross-project database. Each .pur board is self-contained. A fashion designer working with multiple garment types, collections, cuts, and patterns explicitly requested folders, tags, and tabs on the PureRef forum in 2022; the feature has not shipped as of v2.1.3. [Source: pureref.com/forum/read.php?3,2698] Finding a specific image in a large board means scrolling visually through hundreds of thumbnails.

refern

refern builds a persistent SQLite index of your folder on disk. Every image gets full-text search by filename, description, notes, source URL, creator, and tags. 14+ inline operators let you run queries like tag:anatomy rating:>=3 or color:#c24a1b or is:duplicate. Visual similarity search finds images with similar composition and color distribution. Smart folders are saved search queries that auto-populate as you add images.

Verdict: For anything beyond a handful of images you know by heart, the library gap between Kuadro and refern is large. PureRef falls in the same gap; the difference is that PureRef's canvas is genuinely excellent, while Kuadro offers neither a canvas nor a library.

Canvas and overlay

Kuadro

Kuadro has no unified canvas. Every image is its own floating OS window. This makes multi-monitor use natural (each image lives on whichever monitor you drag it to) but means you cannot save a moodboard as a single composed file. A Kuadro .ref preset saves image paths and window positions, not a composited board you can share or archive as one piece. [Source: saashub.com/compare-pureref-vs-kuadro]

The per-window approach does make "paint through" per-image: you can lock individual images for clickthrough while leaving others draggable. One reviewer noted a frustrating limitation: locking in some workflows applies globally, not per-window. [Source: animationandvideo.com 2020 review]

PureRef

PureRef's infinite canvas is genuinely excellent. The v2.0 "pin above a specific application" feature is the best always-on-top implementation among these three tools. Click-through mode with built-in color picker lets you eyedrop hex values from reference images directly into Photoshop or Blender without switching windows. Groups, hierarchy, shapes, and rich-text annotations make large boards navigable.

The .pur file embeds all images into a single binary. A save interrupted by power loss or a full disk can corrupt the file and lose references. Users have reported losing months of work to this. [Source: pureref.com/forum/read.php?5,1367] A .pur.old backup exists but is not prominently documented.

refern

refern's infinite canvas supports layers and groups (nestable, named, with optional colored backgrounds), text elements, 9 shape primitives, freehand drawing, image filters (brightness, contrast, saturation, hue), and non-destructive crop. The canvas window supports always-on-top, adjustable transparency, and mouse clickthrough for paint-over workflows, covering the same overlay use case as Kuadro and PureRef.

Canvas files are saved as .refern-canvas JSON on disk alongside your images, not inside a binary blob. Your originals are never copied; refern only stores an index and thumbnails.

Verdict: For the canvas overlay use case, PureRef is the most polished of the three. refern is comparable and adds library integration that PureRef lacks. Kuadro's per-window approach works well for simple floating references but cannot produce a saved moodboard.

Relationships and graph

Kuadro and PureRef both have no concept of typed relationships between images, no backlinks, and no graph view.

refern adds typed entity links across your library: images can be grouped (fan cards in the grid), linked to other images (cross-reference), marked as derived from another (crop provenance), or placed in canvases with backlinks. A navigable relationship graph shows all folders, images, canvases, groups, and the links between them, similar to how Obsidian maps notes. This is the "what if Obsidian had pictures instead of notes" use case that neither Kuadro nor PureRef approaches.

Platform support

If you are on macOS or Linux and have been using Kuadro, you are already using a tool that is officially not supported on your platform. PureRef and refern both run actively on all three platforms.

Pricing

Kuadro wins on price: it is free with no conditions. PureRef's pay-what-you-want personal tier is also effectively free for students and non-commercial artists, which gives it a major adoption advantage in schools and early-career pipelines. refern's $30 one-time covers commercial use at a single tier with no subscription.

Full feature comparison

Who should choose refern

Choose refern if:

• You have more than a few dozen reference images and want to find them later by keyword, tag, color, or visual similarity.
• You are on macOS or Linux and Kuadro is not an option.
• You want a moodboard canvas and a searchable library in the same app, without switching between two tools.
• You collect references from the web and want a browser extension for one-click saving directly to your library.
• You want your files to live in a normal folder on disk, indexed in place, with no proprietary binary format that can corrupt.
• You use Eagle for organization and want to import your existing library (refern reads Eagle folders, tags, ratings, sources, and notes).
• You want a relationship graph across your images, canvases, and folders.

Who should choose Kuadro

Kuadro is a reasonable choice if:

• You are on Windows only.
• You only need a handful of floating reference windows while you paint and will never need to search or organize them.
• You are not willing to spend $30 on a reference tool.
• The portable .exe with no installation footprint is important for your setup (shared machine, USB workflow).

Be aware that Kuadro has had very low development activity since 2018. If long-term maintenance matters, PureRef or refern are safer bets. Even BeeRef, an open-source alternative listed on AlternativeTo, is more actively maintained than Kuadro.

Who should choose PureRef

PureRef is a strong choice if:

• You primarily use per-project moodboards scoped to one assignment, not a growing cross-project library.
• You are a student or early-career artist who cannot spend $30 now (PureRef is effectively free for personal use).
• You rely on the click-through color picker (eyedrop hex values from reference into your painting app) specifically.
• You are already deeply habituated to PureRef's canvas interaction model.

You can also use PureRef and refern together: PureRef as the overlay canvas while actively working, refern as the library you search and tag between sessions. Many artists find this hybrid makes sense.

For a detailed side-by-side of refern and PureRef specifically, see the refern vs PureRef comparison.

Switching from Kuadro to refern

refern does not require a migration wizard. Your images stay exactly where they are on disk. Point refern at your existing reference folder and it will index everything in place, generating thumbnails and reading EXIF/IPTC/XMP metadata automatically.

If you have been using Kuadro's URL-open feature to view web images that are not saved locally, you will need to use the refern browser extension (Chrome, Firefox, Safari) or drag images into the browser to add them to your library properly. refern stores your files in a real folder on disk, so references you want to keep need to be actual files, not in-session URL loads.

Layout presets (.ref files) do not import to refern; the canvas is a different model. Recreating a board takes a few minutes of drag-and-drop onto the refern canvas.

If you are coming from PureRef, the refern vs PureRef comparison covers migration from .pur boards in detail.

To learn more about what makes a good reference manager, see what is a reference manager.