Peter Hancock: Face PCA

These components are derived from a set of fifty male and fifty female young adult faces, all facing the camera with nominally neutral expressions.  A total of 236 keypoints are located on each face.  The images are then adjusted, by rotation, translation and scaling, to put the pupils in the same location.  Principal Component Analysis was carried out on the sets of coordinates.  The changes they describe are illustrated by applying the "Eigenshape" vector to the coordinates of the average of all the faces.  Each original face was also morphed to the average shape, and PCA carried out on the resultant shape free images, to produce "Eigenfaces".  The effects of these can also be animated by adding and subtracting from the average face. 

Shape components 1-5

The first is face size and it can be seen that, despite normalising for pupil centres, the smaller heads also tend to be female.  There is also an element of sex apparent in the second component, which principally codes nodding of the head.  In this set, it seems that the women tend to look down more than the men (and these are all police officers, so should be quite confident!).  The third codes length of face, the fourth attempts to capture shaking of the head, given the limitations of fixed position eyes.  The fifth suggest that people with a longer fringe have more protruberant ears!

Shape components 6-10 

I shan't attempt to describe each of these next five components.  However, the seventh component is apparently trying to capture something about head tilt, again constrained by having the eye locations fixed.  Note also the way the last two capture aspects of the differences between males and females - look at the eyebrows on 9!

Image components 1-5

These first five image components clearly have a lot to do with lighting, but note that the second component also codes strongly for sex of the face.  Although the lighting was supposed to be consistent, it would seem that the male faces were more lit from above for some reason - something to watch out for if trying to do sex classifications on this set of faces! 

Image components 6-10

The next five image variations are also hard to describe, but note that the seventh one (middle) also codes face sex.  

Images copyright Peter Hancock, March 2000.


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