When developing landscape photos, the problem often arises that individual areas of the image, especially very bright or overly dark areas, have a color cast or colors that look too intense or too pale. Changing contrast or saturation is more likely to intensify the phenomenon. Good masking and selection functions are must-haves for landscape photographers.

Both free and commercial RAW developers now offer extensive tools for selective image processing. But of all the open source programs, only darktable has offered these features thus far. Although darktable is basically an excellent piece of software, there are drawbacks for some users. It takes a bit of getting used to, and you have to thoroughly understand what is going on to achieve good results. In addition, darktable only runs really smoothly if you have a fast graphics card.

The release of RawTherapee 5.9 [1] in November 2022 after several years of development added the ability to modify specific areas of an image in an intuitive and effective way [2]. Developer Jacques Desmis was inspired by the ingenious selection technology of the popular Nik plugins when programming the function. The good thing is: The program is a RAW developer with similar performance to darktable [3], but avoids the above-mentioned drawbacks [4].

There is actually only one RAW developer backing RawTherapee, unlike most similar programs. It does not have a genuine management module, but only a kind of file browser or image viewer. Launch the application and use the browser to navigate to the directory where the photos are stored. Double-clicking on a thumbnail opens the photo in the editor. You will find the editing tools on the right.

Preliminary Work

Start by adjusting some of the default settings. Click the button for this and you are taken to a separate window with several tabs. First, you need to take care of two options: the color of the user interface and color management, or automatic detection of the screen profile. RawTherapee's standard user interface is too dark to be able to adjust the intensity of the colors and the image brightness correctly. You can define a lighter color quite a way down in General | Appearence. The TooWaGrey – Average Surround design is recommended, because it comes quite close to a neutral gray.

Then set the program to automatically detect and use your screen profile. To do this, you first need to install a profile in the color settings of the operating system. In RawTherapee Settings, click Color Management, in the Monitor group, check Use operating system's main monitor color profile, and restart the software.

In the default configuration, the tool activates sophisticated, minimally invasive automatic image optimization for RAW files. To get the most out of a photo, you just need to move a few sliders in many cases. As soon as you open a RAW file, RawTherapee automatically applies three processing steps to the image. The Auto tone curve in the Exposure module does most of the work. The program creates the curve by comparing the actual RAW file with the JPEG embedded in the file. It tries to imitate today's typically quite useful in-camera image optimization.

The application enables Input Sharpening (right at the end of the Raw tab). In contrast to conventional sharpening, the highly efficient sharpening method does not take place at the end of the processing, but at the outset, directly after the image has been descreened in the linear RGB color space. The tool also turns on automatic correction of chromatic anomalies.

Lighten and Darken

The sample photo shows a mountain landscape near the community of Lunz am See in the Mostviertel region of Lower Austria. You have to brighten many landscape images to a greater or lesser extent before doing anything else. The camera underexposes them by default to preserve the structure in the brightest areas of the image to the extent possible (Figure 1).

Figure 1: Without automatic image optimization, the original image will appear severely underexposed and low in contrast; this ensures that the structures in the brightest areas are preserved.

To do this, move the Exposure compensation slider in the Exposure module a little to the right. After several attempts, a value of 0.8 proved to be perfect in our tests. Then darken the sky using the gray gradient filter. The tool makes the upper part of the image darker, inserting a smooth transition from light to dark. You can enable the filter using the button in the module's titlebar. Set the Intensity of the effect to about 1.5. Using the sliders lower down, you can adjust other filter properties, such as the position and size, if necessary.

Contrast and Saturation

Next increase the saturation and local contrast. Move the Saturation slider below Exposure to the right approximately to a value of 67 and enable Detail under Local Contrast. This applies an effect that lies somewhere between sharpening and a (global) contrast increase. If you strengthen the effect, this generally increases the clarity of the image.

Internally, the filter uses a blurred mask – which explains the Radius slider that determines the amount of blur. If you scale this value up, the contrast increases. If you reduce it, it affects the finer details, and the image appears sharper. Meaningful values for this controller usually range between 100 and 150.

The Intensity specifies the extent to which the contrast increases. In addition, you can use Dark areas and Light areas to determine whether the effect will be stronger or weaker in some areas compared with others. You need to be careful with this effect: If the values you choose are too high, the image will look too stark. You need a higher value such as 0.75 for the intensity.

Also watch out for halos – unnatural-looking areas that are too light or too dark, which often appear near contrast edges. You can see a halo in the clouds in the sample image: They border directly on the ridge in the left half of the picture. You need to reduce the intensity for the bright areas by setting the slider to a value of 0.5.