I’ve discovered a pretty quick and easy way to do face swaps such as the above using The GIMP. Here’s how:
Obtain images of the subjects whose faces you wish to swap. For best results the faces should be looking in the same direction, and be of reasonable resolution:
Use the Measure tool (Shift-M) to measure the angle and distance between each image’s left and right eye, noting down as you go. You’ll also need to take note of whether The GIMP is measuring the angle above the horizontal axis or below; record the angle as negative for above the line and positive otherwise.
Break out a calculator and divide the head image’s eye distance by the face image’s eye distance, and scale the face image by this factor:
Now rotate the face image by the difference between the two eye-angles:
Copy the result, and paste it onto the head image as a new layer. Halve the new layer’s opacity and line up the two faces using the Move tool (M):
Return the top layer’s opacity to 100%.
Make a copy of both layers, with the face copy on top and the head copy just below:
Now apply a gaussian blur to both. The blur amount should be as high as you can get without non-flesh tones from hair or background interfering with areas you want to transfer to the head image. About 2/3 of the head image eye-distance has worked well for me:
Now set the blurred face layer to divide, and the blurred head layer to multiply. The face image should now be shining through, but with the right lighting and fleshtones around the facial area:
At this point select Copy Visible from the Edit menu, and paste as a new layer.Move the new layer to second from bottom (right above the bottom head layer), and make all layers above it invisible.
Add a layer mask to the newly pasted, colour-corrected face layer. Initialise it to black (fully transparent). Now with the Brush tool draw over the eye, nose and mouth area in white (opaque):
Apply a gaussian blur to the layer mask, et voila:
By swapping layers and re-doing the Copy Visible layer from step 3 one can easily get the reverse image: