Transforming and Cropping the Layers
The first step when replacing parts of one image with a corresponding region of another image is to make sure the details match up in a logical way, and that there are no gaps that will create empty or transparent pixels.
Looking at the second problem first, it’s clear from Figure 2 the background layer is taller than the foreground layer because of edits made in Lightroom. Another thing we need to consider is the scale of the waves in the foreground layer versus the background. Here the background shot has wave patterns slightly larger because of the focal length and distances involved with the shot. To remedy problems of scale, you can scale the background layer using the Transform tool, and then use the Crop tool to remove excess background pixels. Let’s take a look.
To scale a Layer, select it in the Layers panel, then turn off the visibility of the other layer by clicking the eyeball icon. Click the Transform tool (top-most item in the toolbar); a marquee will appear over the active layer. Here I wanted to reduce the scale of the wave patterns slightly, so I clicked the bottom anchor of the Transform marquee and dragged upward several pixels until I got the result I liked (Figure 3).
Figure 3 The Transform tool allows you to scale layers, which is useful for ensuring the details in one layer match the scale of the details in the companion layer.
To make the transform, click the Apply button. Next turn the visibility of your other layer back on, select that layer, then press C to select the Crop tool. Drag a marquee over the region you want to keep, making sure you have not included any of the overflow pixels from the background image. Figure 4 shows this stage of the process; when you’re ready to crop the image, you can click the Apply button again.
Figure 4 Before you begin masking and blending layers, it’s a good idea to crop the image.
If you need to zoom in to examine the image boundaries more closely before cropping, you can use the Pan tool (shortcut H or Spacebar) and Zoom tool (shortcut Z), to re-orient the image preview.