Lens Corrections

First correct the lens distortion that spoils the image and causes the horizon to curve in an arc. To do this, first create a new layer that shows the visible image, that is, the background layer to which you have already applied the other corrections: Click Layer | New | New Layer From Visible. Make sure that the top layer is selected in the Layers dialog box. Now the software creates a whole new layer that covers all previously existing layers. Assign a name of Distortion and click on it in the Layers panel to select it. Then get started with Filter | Start GMIC-Qt.

The program's user interface is divided into three sections. In a relatively narrow column in the middle, you can see the list of available effects. On the left, there is a preview image, and on the right you can see the settings for the currently selected filter. Type distort in the search box at the top. Effects containing this term will then appear in the effects list, including Distort Lens (Figure 9).

Figure 9: Lens distortions are easily corrected with the G'MIC Distort Lens filter.

In the filter setting options, adjust the Amplitude and Zoom sliders. To remove pincushion distortion, drag the Amplitude knob a little to the left. The correct value for our example image is -0.09. However, G'MIC automatically zooms in and crops the image slightly during correction. To zoom out of the image and cut away less, also drag the Zoom slider a little to the left, to the -0.05 value. Confirm the correction by clicking OK.

Now zoom into the image and check it for errors in the 100-percent view. To do this, click on the drop-down list in the lower left corner of the overview window and select 100%. You will then see a small rectangle in the overview. It shows the visible area of the image in the large preview window. The photo still has some weaknesses. It has a bit of color noise, and in some places there are chromatic aberrations (color fringes). Overall, it turns out to be relatively blurry.

G'MIC provides a good filter to remove the noise. Create a new layer from the visible one and assign a name of Noise. Start G'MIC again and search for the Iain's Fast Denoise filter (Figure 10). It lets you reduce the chrominance noise only; this has less impact on the crispness of the image. To do this, increase the value of the Chroma slider to 2.

Figure 10: The G'MIC Iain's Fast Denoise filter offers users the ability to reduce only the color noise.

Chromatic Aberrations

To correct chromatic aberrations, again create a new layer from the visible one, assign a name of CA, and start the Chromatic Aberrations filter in G'MIC (Figure 11). It gives you the ability to remove chromatic aberrations in two colors (the preset colors are red and green).

Figure 11: G'MIC also offers a filter for removing chromatic aberrations.

In our image there are mainly red chromatic aberrations, so you don't need to change the colors. However, blue chromatic aberrations are also very common. In that case, click on the small red box next to Primary Color; a small color selection window appears. Press the Pick Screen Color button there. The cursor now turns into a small cross. Click on a chromatic aberration in the preview window of G'MIC and confirm the color change by pressing the OK button at the bottom right.

Now move the preview to the area where the chromatic aberration is most pronounced. In the sample image, it is the zone where the waves and the beach meet. Now move the X Amplitude and Y Amplitude sliders to the left until the chromatic aberrations disappear, and then click OK.

If you now check all image areas in the 100-percent view, you will notice that some chromatic aberrations have been corrected, but new ones have appeared in other places. Let's create a layer mask (in Krita, Transparency mask) to tackle this and fill it with the color black to make the corrections on the top layer invisible. Then paint over the corrected areas with white to fade only them back in.

To do this, right-click on the CA layer and choose Add | Add Transparency Mask from the context menu. A white layer now appears below CA in the Layers dialog box. Select it and click on the fill tool (the stylized bucket) in the toolbox. Check that Black is selected as the foreground color. This is indicated by the icon with the two small squares in the toolbar above the preview window. The upper square appears in the foreground color, the lower one in the background color.

Now click on the image. The mask then fills with black. All the corrections you made on the associated layer become invisible. Now change the foreground color to white and select the brush tool in the toolbox. In the brush settings dialog at the bottom right, make sure that the Basic-1 brush is selected. Now, with the white brush, paint over the areas in which you removed the chromatic aberrations with G'MIC earlier on (Figure 12).

Figure 12: Use a transparency mask to mask the areas of the image where editing has created new image defects.

There are still two editing steps to complete. The fragment of ground overgrown with grass in the lower right corner and the blades of grass in the lower left spoil the overall impact. Time to remove them with the Clone Brush. Then increase the sharpness of the image using the Sharpen filter.

Removing Image Elements

Again, create a new layer from the visible image, name it Retouch, and select it in the Layers dialog box. Select the Brush tool in the toolbar, and then find the Clone Brush bottom right in the Brush Presets dialog box. The easiest way to find it is to type clone in the search box at the bottom of the dialog box. The brush is labeled with a folding rule. If you now move the mouse pointer into the preview window, you will see two small circles next to each other, with a cross in the left one.

The circle with the cross indicates the target area, and the empty one the source area. Change the brush size using the blue and white bar in the toolbar above the preview window. Set a size of about 300 pixels there for removing the ground fragment. Hold down Ctrl and move the circle with the cross to an image area above the ground fragment (Figure 13).

Figure 13: The Clone Brush helps to remove distracting image elements.

Press the left mouse button briefly and then release Ctrl. Now move the circle with the cross to the area you want to retouch. Hold down the left mouse button and paint over the entire area. The source area automatically moves with the target area. Follow the same approach when removing the blades of grass, but choose a far smaller brush for this.