We've all tinkered with Photoshop's Layer Blending Modes. Some we can't live without, and some are so obscure they just seem useless. (Let me assure you- they all have a purpose in life!) Let's take a look at one of Photoshop's least appreciated Blending Modes: Difference.

Without getting incredibly technical here, Difference Mode inverts the pixels on a layer and highlights the "different" pixels below. When pixels match perfectly, it appears as black.

When I was doing full-time retouching, I had to do so many head/eye swaps it was ridiculous. I learned the fastest way to line up a face was to use Difference Mode. (Yes, the alternative is to reduce Layer Opacity, but it still leaves room for error. Too much fiddling and your eyes are ready to bug out!)

So here you have the world's quickest head swap:

Step 1:

Make a rough selection of the "donor" face you'd like to transplant. Select your Move Tool (V) and drag from inside your selection to the document that will receive the new face.

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Step 2:

Move the new Layer roughly in place.

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Step 3:

Change the Layer Blending Mode to Difference. (Yes, it looks totally Sci-Fi, but trust me, this helps!)

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Step 4:

Use the Free Transform command (CMD/CTL+T) to manipulate the Layer into place. Remember that black areas show pixels that match. Highlighted pixels are different than the pixels below. When you have the eyes and nose matched up close enough, go ahead and commit to your transformation.

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Step 5:

Change Layer Blending Mode back to Normal.

Step 6:

Hold the CMD/CTL key while you click the "Add Layer Mask" button at the bottom of your Layers Palette. Instead of adding a white mask as the default, it adds a black mask, hiding the entire Layer.

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Step 7:

Hit "D" on your keyboard to reset foreground/background colors. With your Paint Brush (B), paint with white and black to reveal the donor face.


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Once you get this technique down, you'll be swapping heads in 10 seconds flat!