L*a*b* Fine Tuning

The color of the grass in the foreground is a bit too intense now, while the mountains in the background – and dark colors in general – appear too pale. You can correct these details using the Lab module in Exposure.

As the name of the tool suggests, it does not operate in the RGB color space (i.e., with the three color channels of red, green, and blue), but in the L*a*b* color space. In this space, the photo is made up of three channels: L* (lightness), a*, and b*. L* only stores brightness information. The a* channel stores the intensity and tone of the colors green and red, while the b* channel contains information on blue and yellow. For certain editing steps, especially when precisely adjusting the hue and saturation, you will achieve better results in L*a*b* than with tools that work in the RGB space.

The tool has six (initially hidden) curve types that let you manipulate the luminance, hue, and saturation (or chromaticity) of specific colors or tonal ranges. The curve designations CC, CH, CL, HH, LC, and LH are abbreviations (see Table 1).

The top three curves exist in many other RAW developers and photo editors, too. For example, show CH by clicking on the triangle and then selecting Min/Max Control Points from the menu. You will now see a square divided horizontally in the middle by a spline. At the bottom edge, there is a rainbow color gradient. There are also six verticals in red, yellow, green, cyan, blue, and violet. If you click on the point where the yellow vertical line intersects the horizontal spline and drag it up or down, the yellow tones in the preview become stronger or paler. You can use the LH and HH curves in a similar way to manipulate the brightness and hue of individual hues (Figure 2).

Figure 2: After some basic brightness, contrast, and saturation correction, the grass looks too intense, while the mountains are too pale. This can be fixed with the help of the L*a*b* curves.

The lower curves are a slightly more unusual. In the example, I will mainly be focusing on CC and CL. Select the Parametric or Standard curve type. In CC, four sliders appear under the parametric curve, dividing the colors into four groups. Neutral lets you further wash out or intensify near-white, gray, or black colors. In the case of the sample photo, this mainly means the clouds.

It won't hurt to reduce the color here. Because I have globally intensified the colors with the saturation slider in the exposure module, they have acquired a slight color cast. Set the value to -67. The next slider lets you change matte colors, which is useful for the forest and mountains. Choose, say, 50 here. Finally, I'll reduce the intensity of the pastel colors, which mainly means the grass (Figure 3).

Figure 3: Use the CC, LC, and CL curves to independently manipulate saturation and brightness for saturated, matte, and pastel colors and shadows, depths, and highlights, respectively.

In the next step, select the Standard curve type for CL. Click the top button in the vertical toolbar to the right of the curve diagram. When you move the mouse into the preview window, RawTherapee shows you – in the curve graphic – the area of the curve that holds the color you are currently pointing to. You can increase the intensity of dark colors by clicking a point near the bottom of the curve and dragging it upward. Initially, even light colors have become more intense, because the upper half of the curve has automatically shifted upward. You can correct this by moving a point in the upper half slightly downward. The curve should now have an inverted S shape.

Detailed Adjustments

Let's highlight the structure of the clouds in Local (hand symbol). Enable the module in the titlebar and click Add in the Settings field. In the preview window, a red-bordered oval with a red circle in the center appears; move this to the clouds. In Spot method in the Tools panel, select Full image. After doing so, the application will only show you the circle. This selects all the colors in the image that are similar to the color below the image.

In Add tool to current spot, select the Local Contrast and Wavelets effect. Further down you will find the matching settings. Although they are similar to the local contrast settings in the Details tab, they also include a Scope slider. You can use it to control how similar the selected colors must be to those in the center of the selection. High values mean that RawTherapee also includes less-similar colors. This is why you only want to set this value to about 25; this applies the effect to the sky only. Then set the value for Radius to 100 and to 0.67 for the Overall Strength.

Now I'll darken the blue mountains in the background a bit. To do this, create another selection as described above, but keep the Normal Spot mode. Move the center of the spot to a blue spot in the area of the mountains. Then enlarge the spot by dragging the four points on the oval outward across the entire mountain. Reduce the number of colors included using Range (Color Tools).

For effects that do not come with their own range sliders, you can control the range with the global slider. These include color tools such as Color and Light. If you restrict the area, the application changes only the blue of the mountains and ignores the clouds, which are also selected (Figure 4). Add the Color and Light tool to this second selection and set the Brightness there to -5.

Figure 4: If you reduce the range of the selection with the Range slider, RawTherapee changes only the blue of the mountains, but not the clouds that are also selected.

To finish up, there are only a few small tasks left to complete. Straighten the image, reduce the noise, and remove the car fragment on the right edge of the image using the spot removal tool. You will find the rotation tool in Transform | Lens Corrections. Basically, you will want to go for the Select Guideline function instead of setting the angle. In Select Guideline, trace a vertical or horizontal line in the preview. In the sample image, for example, the lamp is a good choice for this.

Remove Distracting Objects

To remove distracting objects from an image, enable the spot removal tool in Details. As soon as you click on the pencil icon, the mouse cursor turns into a small cross, and you can set a point to remove the car fragment. Hold down Ctrl and click on the offending element. You will then see two small concentric circles at this point. Drag the inner circle outward to make it larger.

Actually, there are two brushes on top of each other now: The place covering the target area is at the bottom, and the one for the source area is at the top. Click on the circles and move the upper brush to the place you want to blend the car with – in this case, an area of the image to the left of the car (Figure 5). Except when removing very small spots, you will typically need to set several points to remove the object completely. Finally, use the pencil icon again to hide the brush marks or the retouched areas in the preview.

Figure 5: The new spot removal tool lets users remove distracting objects, provided they are not too large.