This tutorial outlines an easy way to combine exposures. Often a shot must be exposed twice, once for the highlights and once for the shadows.
These two shots of Tony Grove are both incorrect. The top shot was exposed for the foreground and the bottom for the clouds.
The bottom image could be saved using adjustment layers and proper masking but I like the foreground of the top better so I'll combine them to get what I am really after.
Combining images typically works better when there is a natural separation in the composition. In this case there is a nice line to separate the top and bottom of what I intend the final shot to look like.
First you must bring both images into one file. Double-click the background layer of both images (the text should change from Background to Layer 0). With both images open in the main PS window, grab one of the layers and drag it onto the image of the second. You may need to move the layer order and position to suit your composition. A trick I use is to temporarily reduce the opacity of the top layer until you can see both at the same time. This allows for easy rough positioning.
Next add a layer mask to the top layer. To do this, select Layer, Layer Mask and Reveal All. The two choices are Reveal and Hide all. These are the default states of the mask - all black or all white, meaning all visible or invisible. I prefer to use Reveal All for this procedure.
Next, highlight the newly added all-white mask. Using black, paint in the areas of the image you do not want shown in the final composition. I will typically make a rough pass with a large brush to gain a better sense of what is underneath. You can also decrease the opacity of the top layer again to temporarily reveal what is underneath.
If you make a mistake, go over the area with white, black or somewhere in between. Changing the brush opacity and hardness will help with the difficult areas, as will selections. For this image I used an Intuos 4x5 tablet set to airbrush because the edges are not critical.
