Replacing a Boring Sky

Whenever I see a nice sky I grab my camera, fire off a few shots, and shove them in a folder called skies for future use, so I always have a selection available shot at different times of day.

Two important things when selecting a sky picture to use, the lighting needs to be coming from the right direction and the clounds need to be more or less the right scale, which means they need to have been shot with about the same focal length lens as the main subject. These clouds were lit the wrong way round, from left to right, so I just used the 'horizontal flip' in Photoshop to reverse the picture.

The next thing to do is get rid of the old sky. In the 'layers' pallete double click on the background layer and click OK to make the layer into 'layer 0' instead of the background layer. This will allow us to delete the sky and slide other layers underneath the main picture.

Selecting

Next we need to make the selection. The quality of the selection, the position and smoothness of the transition, is what will ultimately make our picture believable or not, so take great care at this stage to get it right. There are various tools available for making selections, in this case, because the sky is pretty much all one colour and tone, the best tool to use is the 'magic wand'. The default tolerance setting is 32 which will do fine here as there is a lot of contrast between the sky and the land. If you were to use the selection as it is now you would notice two things wrong. The transition would be too sharp and there would most likely be a light grey line where the selecting tool didn't quite make it to the edge. So to avoid this we need to 'expand' the selection by a few pixels and the 'feather' it by a slightly lesser amount. This will take us over the edge of the horizon line and nibble a bit off the top of the mountains. Then the 'feathering' will soften the edge a little.

Although a photograph may look sharp enough, when you view the picture at 100% magnification, you will see that the lines are not as sharp as you though. The idea with the feathering is to try to match this fuzziness as near as you can.

If you look back to the original photo you will see that there is a lot of fussy detail right on the horizon, trees and bushes and various man made objects. Because we are trying to make a fuzzy edge without any obvious lines, most of this detail will disappear. However we are not making a map, I think it is better to simplify the lines a little.

After you are happy with the selection just press the delete key and the sky will disappear leaving you with a picture similar to the one below. The land and the sky will remain on separate layers so, if you spot anything you don't like after the sky goes in, it's easy enough to tidy up using a layer mask.