Before we get started you will need to have an image of just a sky that you want to use. I have a collection of sunset skies, plain blue skies, cloudy skies, etc, etc. Note that this technique will not work in Elements because you cannot easily add a layer mask to a pixel based layer. So here we go.

1- Open the main image with the bald or bland sky. Also open the image of the sky you prefer from your collection of skies.

2- Use the move tool - keyboard shortcut 'V' - while holding down the shift key to drag the sky image on top of the main image. Holding the shift key down will make sure the sky is centered in your main image. You will now have two layers. If need be you can resize or move the sky by going to menu bar and selecting 'edit> free transform'. Grab the handles and transform to your liking and hit 'return' when done to commit the changes.

3- Next click on the background layer to activate it and from the menu bar go to 'layer > duplicate layer'. Drag the background copy so that it is above the sky which is probably labeled 'layer 1'. Your layers palette should look like this.

4- Now here's the tricky part. With the background copy targeted, select the sky with whatever selection tools work best for you and the particular image. The color range tool is probably the best as long as none of the colors in the sky are also in the main part of the image. You could also use the magic wand tool or the quick selection tool if that works better. The success of this sky replacement technique really hinges on how good a job you do in selecting the sky that needs to be replaced. Hopefully your selection looks something like the image below.

5- Now matter how good the selection looks at this point, it still needs to be refined because there will be fringes of sky intermixed with the main part of the image that the selection process did not pick up. From the menu bar go to 'select>modify>expand' and set the value to 2 pixels. This will expand the selection to include those fringe areas not picked up by the selection tool you used.

6- From the menu bar, go to select>inverse'. This will invert the selection so that everything but the sky is selected. Now with the background copy still active, click on the add layer mask icon at the bottom of the layers palette as shown by the red arrow in the image below. You now should have a layer mask on the background copy which will allow the sky layer underneath to show through.

7- Hopefully you achieved a good result. If there are still parts of the old sky showing through, you can go back in the history palette to the step just before you expanded the selection and redo step 5 (above) with a value of 3 or 4 pixels. If you have a version of Photoshop with the refine edge command, this may give you a better result than simply expanding the selection. You can also paint on the layer mask with either a black or white brush to either block or reveal parts of the background copy.

8- Since everything is on a separate layer you could easily create an adjustment layer just above the sky to make it more dramatic without affecting the main image.


How to replace a sky in Photoshop