Using an alpha channel to create a shadow
Just as different information in an image is stored on different layers, channels also let you access specific kinds of information. Alpha channels store selections as grayscale images. Color information channels store information about each color in an image; for example, an RGB image automatically has red, green, blue, and composite channels.
To avoid confusing channels and layers, think of channels as containing an image’s color and selection information, and think of layers as containing painting, shapes, text, and other content.
You’ll first convert the transparent areas of the Model copy layer to a selection, and then fill it with black on another layer to create a shadow. Because the selection will be altered to make the shadow, you’ll now save the current form of the selection as an alpha channel so that you can load it again later if needed.
In the Layers panel, Ctrl-click (Windows) or Command-click (macOS) the layer thumbnail icon for the Model Copy layer. The masked area is selected.
Choose Select > Save Selection. In the Save Selection dialog box, make sure New is chosen in the Channel menu. Then name the channel Model Outline, and click OK.
Nothing changes in the Layers panel or in the document window. However, a new channel named Model Outline has been added to the Channels panel. The selection is still active.
Click the Create A New Layer icon () at the bottom of the Layers panel. Drag the new layer below the Model Copy layer so that the shadow will be below the image of the model. Double-click the new layer’s name, and rename it Shadow.
With the Shadow layer selected, choose Select > Select And Mask. This loads the current selection into the Select And Mask task space.
Click the View menu in the View Mode section of the Properties panel, and choose On Black.
In the Global Refinements section, move the Shift Edge slider to +36%.
In the Output Settings section, make sure Selection is selected in the Output To menu, and then click OK.
Choose Edit > Fill. In the Fill dialog box, choose Black from the Contents menu, and then click OK.
The Shadow layer displays a filled-in black outline of the model. Shadows aren’t usually as dark as the person who casts them, so you’ll reduce the layer opacity.
In the Layers panel, change the layer opacity to 30%.
The shadow is in exactly the same position as the model, where it can’t be seen. You’ll shift it.
Choose Select > Deselect to remove the selection.
Choose Edit > Transform > Rotate. Rotate the shadow by hand, or enter -15° in the Rotate field in the options bar. Then drag the shadow to the left, or enter 545 in the X field in the options bar. Click the Commit Transform button () in the options bar, or press Enter or Return, to accept the transformation.
Click the eye icon for the Episode Background layer to make it visible, and delete the Model layer (the one without the mask).
Choose File > Save to save your work so far.