How to Test the All-New gThumb 4.0 Alpha with GTK4 and Libadwaita

Introduction

If you've been using gThumb as your go‑to image viewer and organizer on Linux, you're in for a treat. The open‑source tool has undergone a massive transformation: it's been rewritten in Vala and ported to GTK4 and Libadwaita, giving it a modern, polished look that’s barely recognizable from the old version. An alpha build of gThumb 4.0 is now available for testing, and it brings support for WEBP and PNG animations, JXL export, and a handy censor filter to pixelate or blur parts of an image. This guide will walk you through everything you need to get the new gThumb 4.0 alpha up and running, explore its revamped interface, and try out its fresh features. Ready to see what all the buzz is about? Let’s dive in.

What You Need

• A Linux distribution (Ubuntu 22.04 or later recommended, but any distro with Flatpak support works)
• Flatpak installed on your system (see Step 1 for installation if needed)
• Flathub repository enabled (the beta channel for gThumb 4.0 is hosted there)
• A stable internet connection to download the package
• Basic familiarity with terminal commands (optional but helpful)

Step‑by‑Step Guide

Step 1: Install or Update Flatpak and Flathub

First, ensure you have Flatpak installed. Open a terminal and run:

sudo apt update
sudo apt install flatpak

If you’re on a non‑Debian distro, use your package manager (e.g., sudo dnf install flatpak for Fedora). Next, add the Flathub repository (the main source for Flatpak apps):

flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo

Optionally restart your session or log out and back in to ensure Flatpak is fully integrated.

Step 2: Install the gThumb 4.0 Alpha from Flathub Beta

gThumb 4.0 alpha is available on the beta channel of Flathub. First, add the Flathub beta remote:

flatpak remote-add --if-not-exists flathub-beta https://flathub.org/beta-repo/flathub-beta.flatpakrepo

Then install gThumb from the beta channel:

flatpak install flathub-beta org.gnome.gThumb

You’ll see a list of available versions – choose the latest alpha build (e.g., 4.0‑alpha). Confirm the installation and wait for it to complete.

Tip: If you get errors, ensure your Flatpak version is up to date (flatpak update).

Step 3: Launch gThumb 4.0 and Explore the New UI

After installation, launch gThumb from your application menu or run:

flatpak run org.gnome.gThumb

You’ll immediately notice the revamped interface. The GTK4/Libadwaita port brings a modern look with cleaner toolbars, adaptive layouts, and native dark mode support. The window feels more polished and responsive. Take a moment to open an image and explore the reorganised menus – the sidebar now uses a collapsible design, and the zoom controls are more intuitive.

Step 4: Test WEBP and Animated PNG Support

One of the new features is support for WEBP images (both static and animated) as well as animated PNG (APNG). Find a sample WEBP file (you can download one from the web) or an APNG file, and open it in gThumb. You should see the animation play smoothly right inside the viewer. If you don’t have any, create a simple test: convert a short video to WEBP using a tool like ffmpeg, then open it with gThumb.

Step 5: Export Images in the JXL Format

gThumb 4.0 now lets you export images in the JPEG XL (JXL) format, which offers better compression and quality. To try it:

1. Open an image in gThumb.
2. Go to File > Export or press Ctrl+E.
3. In the export dialog, choose “JPEG XL” from the dropdown format list.
4. Adjust quality settings as desired (higher number = better quality).
5. Select a destination and export the file. Open it later to verify the JXL format.

This feature is especially useful if you’re archiving images or working with modern web formats.

Step 6: Try the Censor Filter (Pixelate or Blur)

Another handy new addition is the censor filter, which lets you pixelate or blur parts of an image. Here’s how to use it:

1. Open an image you want to edit.
2. Click Edit > Filter or press Ctrl+F.
3. In the filter panel, look for the “Censor” option (it might be under “Effects” or “Distort”).
4. Select either pixelate or blur, then click and drag over the area you want to obscure.
5. Adjust the intensity with the slider. The change is applied in real time.
6. Save or export the modified image when you’re satisfied.

This is great for hiding faces, license plates, or any sensitive information before sharing images.

Step 7: Compare with the Old Version (Optional)

If you still have the older gThumb (3.x series) installed, you can run both side by side to appreciate the visual overhaul. The stable version can be installed via normal package manager. Launch the old one and the new alpha – you’ll notice the GTK4 version feels snappier and has a more consistent design with other GNOME apps. The Libadwaita integration also means gThumb 4.0 adapts to your system’s accent color and dark mode preference automatically.

Tips and Conclusion

Remember that gThumb 4.0 alpha is still a work in progress. Expect some bugs and incomplete features – this is normal for pre‑release software. If you encounter issues, report them on the official gThumb issue tracker. Also consider backing up your existing image library before heavy testing, as alpha builds might have unexpected behavior. The new censor filter works best on JPEG and PNG files; with WEBP and JXL, results may vary. For best performance, keep your graphics drivers up to date. Enjoy exploring this fresh take on a classic tool!