10 Remarkable Changes in gThumb 4.0: The GTK4 Overhaul You Need to Know

gThumb, the classic open-source image viewer and organizer, has undergone a radical transformation with its 4.0 alpha release. Ported to GTK4 and libadwaita, and rewritten in Vala, this update introduces a sleek new interface, modern file format support, and innovative editing tools. Whether you’re a longtime user or new to the application, these ten highlights will show you just how much gThumb has evolved. From animation handling to privacy filters, here’s what’s new and noteworthy.

1. A Complete Rewrite in Vala

The shift from C to Vala isn’t just a technical footnote—it’s a strategic move that enables faster development and easier maintenance. Vala’s modern syntax and GObject integration allow gThumb’s developers to write cleaner, more efficient code. This rewrite paves the way for future enhancements and ensures the app stays performant on new Linux desktops.

10 Remarkable Changes in gThumb 4.0: The GTK4 Overhaul You Need to Know — Source: www.omgubuntu.co.uk

2. GTK4 and libadwaita Under the Hood

gThumb 4.0 adopts GTK4 and libadwaita, aligning it with GNOME’s latest design principles. This isn’t just a visual refresh; it brings improved touch support, smoother animations, and better memory handling. The libadwaita library provides consistent styling with modern GNOME apps, making gThumb feel like a native component rather than a holdover from older GTK versions.

3. A Stunning Visual Overhaul

The most obvious change is the interface itself. Gone are the dated GTK3 gradients and rough edges. The new design features clean whitespace, rounded corners, and adaptive toolbars. Buttons and menus are redesigned for clarity, and the thumbnail grid adopts a fluid layout that works beautifully on both small and ultrawide screens. It’s a transformation that makes the app barely recognizable compared to its predecessor.

4. Support for WEBP and PNG Animations

Modern web uses animated PNG and WEBP files, and gThumb now handles both natively. You can view frame-by-frame animations, control playback speed, and export individual frames. This makes gThumb a viable tool for scanning web graphics and lightweight motion assets without needing a dedicated animation viewer.

5. Export Images in the JPEG XL (JXL) Format

JPEG XL is the next-generation image format designed to replace JPEG with better compression and quality. gThumb 4.0 adds export support for JXL, letting you save high-quality photos at smaller file sizes. For photographers and archivists, this is a major step forward in reducing storage while preserving detail.

6. A New Censor Filter for Privacy

Privacy is increasingly important, and gThumb now includes a censor filter that can pixelate or blur selected areas of an image. Whether you’re redacting sensitive information, obscuring faces in screenshots, or creating artistic effects, the tool is intuitive: draw a rectangle, choose pixelation strength or blur radius, and apply. The filter is non-destructive and can be adjusted later.

7. Alpha Testing Stage – What to Expect

The current release is an alpha build of gThumb 4.0, meaning it’s functional but may contain bugs or incomplete features. Early adopters can test the new UI, animation support, and censor filter, but production use isn’t recommended yet. Feedback from this stage will shape the final stable release, and the developers encourage community bug reports.

8. The Old UI vs. New UI: A Night-and-Day Difference

Comparing the 3.x version to the 4.0 alpha reveals a complete makeover. The old interface felt crowded, with thick borders and dark menus. The new one breathes with light theme defaults, subtle shadows, and consistent iconography. Toolbars float, sidebars collapse elegantly, and the status bar is simplified. It’s the difference between a utility from 2010 and a modern app from 2025.

9. Improved Performance and Responsiveness

Beyond looks, the GTK4/libadwaita port brings tangible speed gains. Image loading is snappier, thumbnails render without lag, and scrolling through large folders is smoother. The rewrite in Vala reduces overhead, and GTK4’s rendering engine optimizes for modern GPUs. Users on older hardware will also notice less memory consumption during batch operations.

10. What’s Next for gThumb 4.0?

The alpha is just the beginning. Planned features include enhanced raw image support, additional export formats (like HEIF), and deeper integration with GNOME’s file manager. The team also aims to refine the censor filter with AI-assisted detection and add batch processing capabilities. The roadmap hints at a stable 4.0 release later this year, promising a robust successor to the beloved gThumb.

gThumb 4.0 represents a bold leap forward for the open-source image tool. With its modernized codebase, fresh design, and powerful new features like JXL export and a privacy filter, it’s poised to reclaim its place as the go-to image viewer for Linux users. The alpha is rough, but the potential is immense. Familiar yet fresh, gThumb is ready for the next decade.

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