Ever since 2.8.0 was released in 2012, rumors of the next major version, 2.10, have been rampant on the Internet. Although the project roadmap [1] doesn't name the date that Gimp 2.10 will be released, it will most likely rely completely on the new Generic Graphics Library (GEGL) [2], which supports higher bit depth images than Gimp currently supports and non-destructive editing.

With non-destructive editing, the GEGL function preview is always shown directly in the image window – a huge advantage, considering the tiny partial preview windows offered in current plugins. Editing with the library functions is always graph-based [3]: Although this might seem complicated at first sight, it offers exceptional advantages, as you will see.

In the recently published Gimp 2.8.14, you can already see the first fruits of the developers' labors. However, GEGL integration in this version does not work as well as in the developer version of Gimp 2.9: In version 2.8.14, the functions run far slower than they will in future releases. The GEGL operator under the Tools menu currently groups the features that have already been implemented (Figure 1). An icon for this tool will also appear in the Toolbox if it has been enabled in Preferences (see the box "GEGL in Gimp 2.8").

Figure 1: Gimp 2.8.14 offers all the existing GEGL tools in a drop-down box.

Figure 2: Enabling the GEGL Operation tool in the toolbox.

If you select a GEGL tool, a customized dialog appears in the second step that allows you to configure the function parameters. In Gimp 2.8, this is not particularly useful because you only have buffers with color depths of up to 8 bits. For HDR features, such as mantiuk06, fattal02, and reinhard05, this would be like applying the functions directly to JPEG images. Although you can be successful [4], it hardly taps into the features' true performance.

One of the GEGL operations that is already working pretty well is color-temperature correction, which recomputes the color temperature of an image. To do this, you define the color temperature of the original image and the desired color temperature: The function then converts the colors in the image accordingly. In many situations, this is your best option for applying subtle color changes or repairing a botched white balance.

Gimp 2.9

In the remaining sections of this article, I refer to the latest developer version of Gimp (Gimp Git), which is released at regular intervals. I tested on Arch Linux; all Gimp versions are numbered 2.9.1 followed by the checkout date and the revision number (e.g., 20140604.gfd928cd-1). Most of the versions in the Git master are sufficiently stable for use in smaller projects. (See the "Installing Gimp 2.9" box.)

# yaourt babl
# yaourt gegl
# yaourt gimp-git

After launching Gimp 2.9, the first thing you will probably notice is the greatly extended toolbox (Figure 3). New icons are not yet available for all the new tools, so initially you will need to read the tool tips to avoid guesswork. The new tools currently residing in the toolbox are the Unified Transform tool, the Warp Transform tool, and the Seamless Cloning tool.

Figure 3: The toolbox in Gimp 2.9 (right) contains far more tools than that of Gimp 2.8 (left).

Unified Transform

The Unified Transform tool (Figure 4) is a combination of the well-known Rotate, Scale, Shear, Perspective, and Move transformation tools. Numerous "handles" let you perform different functions in a single step.

Figure 4: The Unified Transform tool groups the functions of five standard tools, with additional options in the Tool Options window on the left.

Although you can basically do this with the Perspective tool in Gimp 2.8, achieving individual transformations in a targeted way with this approach is something nobody is likely to manage in production use. The Unified Transform tool acts on layers, selections, and paths (Figure 5). In the Tool Options window, you can see in the Constrain section which action is currently being performed. Under the From pivot and Pivot sections, you can define how Gimp uses reference points in transformations.

Figure 5: As with legacy tools, you define what the Unified Transform tool actually works on: layers, selections, or paths.

Warp Transform

The Warp Transform is based on the IWarp tool, which is found under the Filter | Distorts menu. Contrary to what you might expect, it has nothing to do with envelope transformation; instead, the tool is used to distort layer content in totally different ways (e.g., stretch, compress, bend, enlarge sections, etc.).

The legacy IWarp tool only provides a very small, moderately useful preview. In the Warp transformation, on the other hand, you work directly in the image window and scale the view for perfect insight into what is going on (Figure 6). As a general rule, you use a tool after selecting the desired functionality in the options of the Behavior drop-down, just like a brush whose Size and Strength you define in advance. Hardness supplements these two parameters and modifies the Strength (Figure 7).

Figure 6: The legacy IWarp tool shows the complete layer in a preview window (top), which makes it difficulty to edit details. In contrast, the new Warp Transform (bottom) lets you customize the view in a targeted way.

Figure 7: The parameters for Warp transformation are configured in the Behavior drop-down.

Warp Transform, however, does not let you create animations. In IWarp, you just enter the number of images for the animation in the second tab of the IWarp dialog, and the filter itself takes care of the competing images between the start and end states.