Post processing: Creating a straight horizon
11 April, 2013
Here is an image:
The image is not particularly interesting besides showing that if the horizon is not horizontal, it can add a big distraction. The nice thing is that it takes less than 10 seconds to correct the problem.
Load the image in gimp, select the measure tool (shift+M) and draw a line along the horizon and read the message on the status bar. In the example image, it is visible that the horizon is 2.3 degrees off. The next step is Layer > Transform > Arbitrary rotation... and type in 2.3 and hit ok. Done.
Rotating the one and only layer in the image will add some transparent pixels in the corners. This can be fixed in some different ways, but the easiest is to make a selection that only contains parts of the original image and then selecting Image > Crop to selection to remove a small part of the image. And the final result:
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