gThumb

gThumb [5] is one of the oldest Linux image viewers. The first version was released in 2001. Like Geeqie, the program was originally based on GQview. Now the version counter has reached 3.6.2, and the application relies heavily on the Gnome desktop capabilities offered by the GTK3 Toolkit. In the header bar of the application window, for example, you can find the control elements for navigation, search, presentation mode, and other functions.

The image viewer has two modes that merge seamlessly. Directly after starting gThumb via the application menu, the program loads the file manager (Figure 4). On the left, you can see a tree structure with the folders from your home directory, including links to the directories Pictures, Videos and Downloads. In addition, there is the entry Computer, which lets you access folders from the entire filesystem, and Catalogs and Selections.

Figure 4: gThumb is one of the old-timers on the Gnome desktop, but it doesn't show its age, because the developers are continually working on innovations.

In the larger center area, gThumb displays the images stored in the selected folder, listing all images by default. Use the Display: field at the bottom of the screen to restrict the display to JPG images or a personal selection – handy if the folder contains RAW images as well as JPGs; otherwise each image would appear twice.

Use the button with the lightbulb bottom right in the window to display a third column. The Properties (file properties including size, format, and metadata), various Details (further information from the Exif data), a Histogram, or a Map (if the metadata contains the geo-position of the photo) appear at the bottom of the column depending on the selection.

Double clicking on an image opens the large format image in edit mode (Figure 5). In the window bar, the button assignments change. You can now switch the application to full-screen mode and scale or rotate the image in the window. After pressing the button with the lightbulb, a sidebar with the image's metadata opens like in the file manager. You can display an overview of the images stored in the image folder by pressing the bottom righthand button. This displays a bar with thumbnails at the bottom of the screen.

Figure 5: gThumb's image processing capabilities go far beyond those of other image viewers. The program lets you perform many typical tasks easily, such as leveling the horizon.

The button with the brush opens the actual edit mode, which offers the usual feature set: adjusting contrast, brightness, and colors, automatic Instagram-style filters, and tools for cropping or mirroring the shot. One especially practical feature is the rotation tool, which automatically removes parts of the image that are no longer needed after straightening the horizon. This saves a number of steps compared to Gimp.

gThumb is a good choice for photographers with a larger image collection who archive their images in a structured way and do not need an image database. It has a very clear and versatile configurable interface as well as useful image-processing functions.

XnView MP

People who have to manage large numbers of images under Windows often use the freeware programs IrfanView [6] or XnView. The latter is now also available for Linux and Mac OS X as XnView Multi Platform (XnView MP) [7]. For private purposes or non-profit organizations (associations, schools, universities), the program is free; commercial users have to purchase a license (single user: EUR29).

Due to the restrictive freeware license, XnView MP is missing from the package sources of almost all distributions; it is only on Arch Linux that you will find the program in the AUR. The program website offers DEB packages for Debian or Ubuntu, as well as distribution-independent TGZ archives, which you only have to unpack.

XnView MP is similar in structure to other image viewers with a folder browser. On the left you see the directory tree, on the right the images stored in the selected folder (Figure 6). You can also use the sidebar to manage bookmarks and categories. In the bar below, the application displays details of the current image and another preview. A double-click opens an image as a new tab in large format in viewer mode (Figure 7).

Figure 6: Freeware instead of open source: XnView MP compares favorably with its competitors and handles sidecar files well.

Figure 7: XnView MP works with tabs. This makes it easy to view and organize multiple images and image collections.

In image management, XnView MP combines image, RAW image and sidecar files into one entry. If you delete an image including the RAW version and XMP file, the tool asks if you really want to remove all three files at once. In practice, however, you often have to adjust the selection logic a little: Canon cameras, for example, write CR2 files in RAW mode, which XnView MP displays as separate images by default.

In the General tab below Tools | Settings | Picture management | Files, select the files that belong together. For example, if you expand the entry for jpg to {ext}.xmp;xmp;exf;cr2;cr2.xmp, then merging of the different image files will work. However, errors still occur: XnView MP reliably deletes and moves images and sidecar files in a single action, but only changes the name of the JPG when renaming images.

The strengths of XnView MP lie in its speed of operation and the nicely configurable handling of sidecar files. Even folders with a larger image collection are quick to display in the application, at least after the initial process of creating thumbnails on first launch. Reviews and ratings help to add order to your photo collection after a whirlwind photography session.

nomacs

Nomacs [8] is based on the Qt toolkit, which makes it interesting for use on KDE desktops. You can use the File menu to load individual images or entire folders. The program displays the contents of directories in the form of small thumbnails (Figure 8). Nomacs gets down to business very quickly, even with folders containing a large number of images.

Figure 8: Nomacs creates a preview when loading folders with many images, even if the data are located on a NAS device on the LAN.

The application displays RAW images along with the JPGs from the selected folder. You can use a filter to restrict the display to certain names or file extensions. So far, however, the program lacks the ability to merge RAW, JPG, and sidecar files. The developers have not yet implemented a proposal for this feature already entered in the bug tracker and planned for nomacs 3.1, not even in the current 3.12 version.

In the overview, you can open images in larger format by double clicking. To go back, select Window | Thumbnail or type the keyboard shortcut Shift+T. Alternatively, you can enable a preview bar for navigating the image folder in the same menu. Much like gThumb, nomac's basic image editing functions can be accessed via the Image Editor menu. In the menus, you will also find more gimmicky functions such as a mosaic image generator.

When it comes to comparing images, nomacs takes a different path than Geeqie, which can split the image view into several areas. You can use Sync | Synchronize to link several instances of the application. The Sync View option tells nomacs to automatically sync the image section in the application windows.

In this way, you can easily compare two shots of the same subject taken in quick succession. If you zoom into an image, nomacs automatically adjusts the view in the second instance to match (Figure 9). In theory, this synchronization also works between different computers on the network, but synchronization over the network did not work in our lab.

Figure 9: In Sync mode, several instances of nomacs can be linked together. If you zoom into an image, nomacs automatically matches the view in the second window.

All told, nomacs proves to be a successful alternative to the KDE heavyweight, digiKam. The Sync function in particular stands out: No other image viewer can compare images so accurately and conveniently down to the smallest detail. For cleaning up and maintaining the image collection, however, it would be helpful to have functions for handling sidecar files and – among other things – a search for duplicate images.