I recently saw a question on another forum asking how to separate an object and its original shadows from their background in Photoshop Elements, in order to place them on a new background. By a strange coincidence, I was working on this technique myself; so it made perfect sense to write it up as a tutorial.
The key to the technique is using the object’s luminance channel – the highlight and shadow areas. By doing this we can isolate the darker areas of the image, using the resulting selection to create a separate shadow layer. In Photoshop we can do this using the composite RGB layer in the Channels panel, or with the Color Range command. In Elements we need to think a little more laterally.
We’ll use a simple object on a plain white background here as it’s easy to select and demonstrate the technique, but it will work with almost any shape and size of image. A good example would for changing the background of a product shot for Etsy or eBay. Although we could simply extract the object on its own and create our own shadow, if we can use the real one, we’ll get a much more realistic result.
We’ll begin by selecting the ball with the Elliptical Marquee tool (keyboard shortcut M). Go to Layer > New > Layer via copy (or press cmd/ctrl + j). We now have a new layer containing just the ball.
Go back to the Layer menu. Select Layer Mask > Reveal All, or click the new layer mask icon in the Layers panel. We’re not going to use this in the way we’d normally apply a mask, however; in this instance we’re going to be using it for a completely different purpose.
Click the background layer’s thumbnail in the Layers panel to make it active again. Go to Edit > Select All (or press cmd/ctrl + a) to select the whole document. Go back to the Edit menu and select Copy (cmd/ctrl + c).
Hold the opt/alt key down. Now click the layer mask’s thumbnail. The image will go white; we’re now editing the mask directly as an alpha channel. Go to Edit > Paste (or press cmd/ctrl + v) to paste a copy of the background layer into the mask. We won’t see anything happen to the image itself, this is OK.
Hold cmd/ctrl. Click the mask’s thumbnail. We now have some of the ball and a small part of the shadow selected. What we have done here is loaded the image’s luminance (highlights and shadows) values as a selection.
Currently the selected area contains the highlights, we need the shadows, of course. Go to Select > Inverse (or cmd/ctrl + shift + i). We’ve inverted the selection so now only the shadows are selected.
Click the background layer’s thumbnail again to make it active. Now click the new layer icon in the Layers panel, or go to Layer > New layer. Make sure the background colour is set to black. Press cmd/ctrl + backspace to fill the selection with black. If we look at the Layers panel, we see a partial version of the ball.
The ball itself appears darker than before; this is because it’s being partially hidden by the mask, so we can see the additional black from the layer below. Right click on the mask thumbnail. Select Delete Layer Mask. The ball looks normal again.
Go to Select > Deselect (or press cmd/ctrl + d). Although we can’t see it at the moment, we now have a perfect copy of the shadow, separate from the ball. To demonstrate: click the background layer’s thumbnail once more. Go to Layer > New Fill Layer > Solid Color. Click OK to accept the default settings. Now use the colour picker to create a new backdrop color.
To make the shadow permanent, click the ball layer’s thumbnail. Now go to Layer > Merge Down (or press cmd/ctrl + e). The shadow is now part of the ball’s layer but still remains semi-transparent, so we could drop the ball onto a completely different image and the shadow would blend into its new background.
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