One of the advantages of using the Paste Into command to accomplish this result is that the layer mask created by the command is not linked to the dramatic sky image. Point out to students that there is no link symbol between the photograph thumbnail and the layer mask thumbnail on the dramatic sky layer, as there is when a layer mask is created the conventional way—by clicking the Add Layer Mask icon at the bottom of the Layers panel. This allows students to move the sky around with the Move tool without disturbing the mask to get just the look they want. The completed composite is saved using Photoshop’s File > Save command. This updates the TIFF with which students started this exercise, so that Lightroom now displays the TIFF as a composite of the dramatic sky and the adjusted statue.
Isolating a complex object with a channel mask This exercise illustrates how to replace the background of a photograph by passing the photograph from Lightroom to Photoshop for selecting, masking, and compositing using a channel mask. Although any Photoshop selection method could be used with this technique, this exercise teaches a selection method—channel masking—that is very useful for making selections of complex edges. This is a relatively advanced selection technique, so keep your students’ skill levels in mind as you decide whether to teach it. Before students start this exercise, make sure they read the Introduction to Channels sidebar in this exercise, which explains color channels in an RGB image. Then walk students through the steps of this exercise, which demonstrate how to use a channel as the basis for a channel mask, which is used to create a selection and ultimately a layer mask. The following summarizes the steps (which are spelled out in more detail in the book): 1 Pass two TIFF photographs from Lightroom to Photoshop—a photograph of a dog that contains a studio background, and a photograph of an outdoor scene— using Lightroom’s Edit In > Open as Layers in Photoshop command. 2 In the resulting Photoshop document, make sure the photograph of the dog is at the top of the layer stack in the Layers panel. 3 Evaluate the red, green, and blue color channels in the dog image to find the color channel with the most contrast (the most difference between light and dark values). In this case, the highest contrast channel is the Red channel. 4 Duplicate the high-contrast Red channel to create the Red copy channel. The Red copy channel is not a color channel like the red, green, and blue channels. It is an alpha channel, which is a special kind of channel whose function is to contain a mask.