For many Landscape Photographers the idea of replacing a sky in Photoshop is considered taboo. For the most part I completely agree that we Landscape Photographers should try to replicate a scene as closely as possible to what the conditions were at the time we snapped the shutter. We also know that Mother Nature often will not cooperate with us on our photography outings. On many occasions it simply isn’t possible to return to an area over many times to re-shoot the same scene in hope of getting that beautiful sky we all hope for. We photographers end up with a dull gray bland sky that simply ruins the feeling we are trying to communicate.
I find it permissible for the purposes of Web display to show photos that have been altered especially when posting a Blog image. I would not advocate selling a gallery wrap or framed print that had an altered sky. The techniques for changing or replacing a dull sky are many and varied. It can be fun and challenging as well to practice different methods. Some of the easiest images to alter a sky are ones that have a very simple transition line between the foreground elements and the sky, void of trees and or other distracting elements.
If you search sky replacement techniques on You-Tube many results will come up, with great tutorials. One of the simplest methods is to make a selection of the sky you want to discard then grab the selection of the new sky from another image and paste into selection of the first image. Another simple method is to simply drag the photo of the undesirable sky over the preferred sky image and using the eraser tool carefully erase away the sky portion of the image until the new sky has emerged. You can also do the same thing with a mask being very careful when erasing around the transition points. Depending on the image one of the hardest thing for me is making the initial selection, in some cases I just won’t attempt replacing a sky as it is just to obvious.
Here are two shots I took at lake Billy Chinook near Madras Oregon on a very dull day. These two images have had skies added to them. If you look at the Billy Chinook Falls image at full resolution you will see an example of the very poor transition line and the terrible selection job I did resulting in an unfavorable image. The other image of Lake Billy Chinook had a much smoother transition line and although not a great job it looks a little more natural than the first image.