A third technique to solve a tilted horizon, first described this post, is the counterpoint to the second technique and a variation of the first technique. Instead of building out, this solution is to crop the blank space also removing a portion of the image.
Here is a Photoshop screen capture from just before the crop is executed. The grid of fine lines is the Crop tool. For example, on the upper right corner a portion of Rathlin Island, the water, a slice of land are removed along with the blank portion.
Note from the Photoshop screen capture, the blank space along the upper margin is NOT removed. To do so will ruin the composition, the top of the hill on the upper left would be removed. Instead, I used the second technique to copy the sky over the blank portion left after cropping.
Click photograph for a larger view. To do this from WordPress Reader, you need to first click the title of this post to open a new page.
The second solution post describes how copying content onto the blank space can cause duplication of image features. In the above example, I need to perfect the image, modifying the clouds OR perfect the copy process to avoid the duplication.
The end result is a view of wildflower meadow, foreground, coastal sheep pastures running up the high hill. Named Greenanmore, the hill is a site notable for a neolithic passage tomb. The distant land across the North Channel water is Rathelin Island.