Image viewers abound under Linux, and some have additional functions that permit universal application beyond the viewer capability. A particularly successful combination is gThumb, which consists of an image viewer together with software that allows the user to perform simple image editing tasks [1].

Installation

The gThumb software was developed for the Gnome desktop. For distributions that use Gnome as their interface, therefore, it is usually already installed. However, the software also runs with most other work environments, which at times leads to extensive dependencies.

You can install gThumb on Ubuntu with a simple:

apt-get install gthumb

You can also install the bleeding-edge version using a specific PPA. Executing:

sudo add-apt-repository ppa:webupd8team/gthumb
sudo apt-get update
sudo apt-get install gthumb

will get the job done. Ignore the warnings: The latest version works fine in Unity.

Or, you can use the Ubuntu Software Center. The package manager resolves the dependencies correctly most of the time. Type gthumb in the HUD and the program will pop up.

Interface Matters

The program welcomes you with an interface that takes some getting used to. It corresponds to the experimental Gnome conventions introduced in version 3. The current image file appears on the upper left side of the window when the program is in editing mode. Thumbnails for other images appear below in a bar that stretches horizontally across the window. To the upper right, you will see a fold-out sidebar that contains various interfaces arranged horizontally. Some of these branch off into the settings. There is no standard menu bar.

Remember that some operating elements usually provided by the window manager started appearing in Gnome 3 inside the application window once "client-side decorations" were introduced. This means that the buttons for minimizing, maximizing, and closing a window appear twice on interfaces that are not based on GTK. However, none of this has an impact on the functionality (Figure 1).

Figure 1: The interface for gThumb takes some getting used to, but it is functional. It also looks clean when the program first starts up.

The individual pictograms on the control buttons are not always readily decipherable by the user. Therefore, the software explains their functions with a tool tip once you hover over the button with the mouse. The buttons to the upper left allow you to change the view of the image and also to rotate it. The buttons at the upper right are used to modify the files.

The button to the far left is properties . Here you will find a listing of the features of the image in the form of a table. The button next to it labeled Edit File branches into the menu for editing. From this menu, you can choose from among seven functions from the colors group. Additionally, it is possible to go back and sharpen the contents later.

The first function in this group is especially interesting. It is called automatic contrast equalization . I used this function during testing to edit landscape images that appeared faded due to strong sunshine or fog. I was able to improve the contrast and saturation considerably without decreasing brightness (Figure 2).

Figure 2: If done correctly, changing contrast improves an image structure greatly without making the image darker.

With the next button over to the right, you can perform a complete color equalization. A slider lets you manually set brightness, contrast, concentration, and Gamma value. You can also adapt the number of colors; however, this is preset to the additive color model [2].

The third button lets you bring the image into sharper focus. Just as with the image editor Gimp, the gThumb software superimposes a small excerpt of the image as a preview. This lets you see whether artifacts are visible due to overly restrictive settings before starting the editing process for the entire image.

A mouse click on the button sitting to the right in colors lets you adjust the histogram. This also has a significant effect on the image in that the software seeks the best possible distribution for brightness across the entire image.

The second row of control buttons in colors let you convert a color image according to gray shades, to invert it, and to correct the red eye effect often seen in photographs taken with a flash of people or animals.

Because the software immediately implements all modifications, you will be able to determine whether the option you have selected actually does what you want. If not, you can reverse the last operation by clicking on the revert button at the upper right of the program window.

The button group labeled rotation exists so the gThumb user has various options for rotating and flipping an image. This functionality is especially important when working with photographs taken with a digital camera in portrait format. The photos will need to be rotated 90 degrees for viewing in landscape format.

The Format group offers functions for cropping an image and modifying its size. In addition to a simple feature for cropping images, gThumb has an option for adapting an image to a standard format.

For example, this option lets you use a mouse click to change the dimensions of an image to the standard 3:2 size so that you can use the image as a postcard. The software overlays a grid onto the image so you can determine the section you want using the mouse.

Seek and Ye Shall Find

If you have large collections of images in your bulk memory, it can become more difficult to maintain an overview of individual albums. gThumb offers an option for searching for duplicates and makes it easier to search through the actual folders stored on the hard drive.

By clicking on the show folders button at the upper left of the editing window, you will be able to see the folders. The software now opens a directory tree on the left side of the program window and shows lists of preview images from each active directory in a large area on the right.

If there are also video files in the directory that has been opened, the software will display the file as a gray box with an integrated video camera symbol. All it takes to open an image is a mouse click. At the same time, gThumb will switch into editing mode (Figure 3).

Figure 3: gThumb opens images directly into editing mode with one click.

When the directories are large and nested, conducting a search by flipping through individual directories can take quite a long time. gThumb therefore has an additional search function that you can start by clicking the search files button to the upper left in the program window.

The window that appears comes with options that let you conduct a targeted and selective search for individual images by entering criteria from a list, and combining these criteria if necessary. Naturally, you can also recursively search the subdirectories (Figure 4).

Figure 4: Being able to conduct a detailed search brings efficiency to the process of browsing extensive directory structures.

Metadata

Additionally, gThumb offers the possibility of editing the metadata associated with the images. You can modify the metadata as you wish with the small dialog found via the Comment button at the upper right in the program window.

Along with comments and keywords, you can save copyright and other information about the image under the other tab.

Likewise, it is possible to completely delete the extensive metadata that typically is included with images produced by a digital camera. To delete this metadata, you first activate the folder view and then highlight the appropriate image that is contained in the list that sits on the right in the window.

Next, click in the upper right on the tools button. If you now select the delete metadata option in the drop-down menu, the software will remove the metadata. If you want to remove the metadata from several images at the same time, then you should highlight all of these and again use tools | delete metadata .

Once you have completed all modifications to your liking, you can store the image in your collection via the save or save as buttons.

Batch Processing

Routine tasks like changing metadata or converting among formats often take a lot of time if numerous images are involved. As a result, the gThumb software offers a batch processing option. This option lets you perform routine tasks on large batches of images once you have set suitable parameters.

The option provides you with functionality for rotating images, converting them into another image format, changing the image size, and modifying the time stamp associated with comments as well as the date of the last modification.

You will find this option once you have highlighted the images to be modified by means of clicking on the button with the monkey wrench symbol. It sits in the upper right of the folder view.

Clicking on this button opens a context-sensitive dialog in which you can set the desired parameters. A click on execute makes the software work through the batch and save the modified files in the specified location (Figure 5).

Figure 5: If you want to modify a large number of images all at once, the batch processing function is a good solution.

Presentation

gThumb also offers a presentation mode that can be controlled both automatically and manually. To start the automatic presentation, click on the offset Presentation button to the upper right in the folder view. Alternatively, you can start and close a presentation by pressing F5.

The software switches into full-screen mode and displays the images in rows in the current directory. Once a five-second display time has elapsed, the next image in the series will appear. If you want to interrupt the presentation, just press the p key.

If you want to move more quickly through the images, you can either use the space bar or the right arrow key. To go back one image, you should use the left arrow key. Pressing the Esc key ends the presentation and takes you back to the folder view. If gThumb is running in a Gnome desktop environment, then you can set the display time for each image via edit | setting | slide show and also choose various fade-out effects. This function is not found in desktop environments that are not based on GTK libraries.

Import and Export

gThumb also can be used in conjunction with social networks and photo services, so it is not just for images stored locally on your home computer. If you want to integrate images from online services into your gThumb collection, you can import them into the software by clicking on the designated button with the gear symbol to the upper right in the program window and selecting import from from the menu that appears.

The software will then ask for the source. A click on one of the selection options creates a secure connection in a new window to the service involved. You can also use gThumb to export images to online albums.

To do this, highlight the images you want to export and then click on the export button at the upper right in the program window. In the context menu that opens, you can select one of the offered services. Afterward, you can upload the highlighted image after authentication in a new window.

Creative Ideas

gThumb offers several functions for creative composition of slideshows to the ambitious photographer. The first step in building a slideshow is to highlight the appropriate images. Then, clicking the Export Button takes you to an option for creating a web album via the menu entry Internet-Album … .

Alternatively, you can archive a mural on a CD or DVD by selecting the Optical storage . A settings dialog for each of the options will open the corresponding composition possibilities (Figure 6).

Figure 6: gThumb also offers options for the creative set, such as this mural.

Conclusion

gThumb is a good way to get many tasks accomplished without much fuss. With Gimp, for example, your work might take considerably more time. gThumb lets you do things like change contrast and brightness, remove red eye effect and crop images to standard formats with just a few mouse clicks.

The tool does not require much getting used to, and the software impresses with its image viewer and presentation capabilities.

The graphical user interface is the only part of the program that may require some practice. The lack of menu hierarchies and the buttons with unusual symbols may mean that the user will have to spend some time figuring out the mechanisms. Once this hurdle has been cleared, gThumb is a very efficient program for use with many routine image processing tasks.