Replacing Skies using Photoshop
For replacement of skies using selection and Paste into.
Open the image (1) in Photoshop that needs the sky replacing.
Select Image-> Image Size and take a note of the size.
Download a selection of replacement skies from the internet and save the images.
Select a suitable sky (2) and open it. Again find out the image size, change it to a larger image size than (1) by editing the width and height in the window.
The two images can now be selected by clicking on their name in the status bar above the Photoshop image screen.
Click on image (2) the sky, go to Select -> All, then Edit-> Copy.
Click on image (1) and use a Selection Tool to select the sky area in the image. Quick Selection, Magic Wand are the best tools to use. If using the Magic Wand set the tolerance to 50 -75, Anti-alias, Contiguous. Should an area of sky be missed, hold down the Shift Key and select it.
Next select Edit -> Special Paste -> Paste into.
Finally go to Layers -> Flatten Image then Save the image.
Sky Replacement using Layer Mask.
Decide on the two images you will be using. Ensure both images are the same size, if not correct their sizing by changing the value in the image size dimensions and OK. In Photoshop use File-> Script-> Load Files Into Stack. This brings up a window with Browse in it. Hit Browse to select the main image, OK. Hit Browse again and OK the replacement sky image. Finally OK the Stack window.
You now have both images as different Layers in Photoshop. The sky layer should be below the main image Layer, if not select the lower Layer with the left mouse button held down and drag the lower Layer up over the above Layer and release the mouse button.
Click in the top main image Layer, it should turn blue, use one of the selection tools to select the sky, the Quick Selection Tool is best. Once the sky is selected I suggest you click on Refine Edges to Smooth and Feather the edge a little.
Ensure the land has been selected, if not use Select -> Inverse to swap it over.
Make sure the top Main Image Layer is selected, click on the Layer Mask Icon that is a small square with a white circle in the middle. It is found at the bottom of the History Panel. The new sky will now replace the original. Ensure the Sky layer is selected so it can be re-positioned using the Move Tool at the top of the Tools Box (an up facing pointer with directions cross).
Finally go to Layers -> Flatten Image. Save the image
Article by Peter B