In our research project we examined the influence of facial symmetry on attractiveness. According to evolutionary theory faces are supposed to be more attractive the more symmetrical they are. In order to test this hypothesis we produced symmetrically optimised versions over a range of different faces (of low, average and high attractiveness). Each of these symmetrically optimised faces was presented to test subjects together with the corresponding original face. The task was to select the face that was perceived as being more attractive. 

There are several ways of producing symmetrical faces: The most common method is creating so-called "chimeric faces". Using image processing software, one half of the facial image is duplicated, mirrored along a vertical axis and finally added to the remaining half of the original face. The resulting, perfectly symmetrical face consists either of two left or two right halves of the original face. But there is one problem: Because faces are not perfectly symmetrical, it does make a difference whether you use the left or the right half as a starting point. Another problem is that, by using this method, birthmarks, pimples or irregular hair structures are doubled, too, so that the overall resulting symmetrical face looks quite odd. 
 

----

Left: Symmetrical face using the left half of the original face. Middle: Original face. Right: Symmetrical face using the right half of the original face.

A clearly advanced and better way to produce individual symmetrical faces is the morphing technique. Morphed images are made from two images of different faces by averaging face shape and then blending red, green and blue intencity (RGB colour) across comparable pixels.  All symmetrical faces we used in our research project were generated by blending together the original face with a duplicate that has been mirrored along a vertical axis. 

In contrary to the Chimaerengesicht, the resulting face does not show a distinct dividing line along the centre of the face, and the question which half to take becomes obsolete. 

Example: If a face has a broad left and a narrow right lower jaw, the mirror image method produces a face with either a broad or a narrow lower jaw on both sides. Avoiding these unpleasant effects, the morphing method automatically calculates the average breadth of the left and right half of the lower jaw. 

In addition, asymmetries like a high-standing or slant eye are levelled out by this method. For our project we used a modified morphing procedure that symmetrized only the face proportions. Skin and hair remained unaltered, which made the resulting face look more natural and life-like. 

----

Left: Symmetrically optimised face calculated by using the conventional morphing technique; bad skin is ameliorated, hair gets blurred, every single feature is reflected, facial hairs and pimples included. 
Middle: Original face. 
Right: Symmetrically optimised face calculated by using our modified morphing technique; only the shape of the face is symmetrized. The skin and hair of the original face remain. Thus, the result looks substantially more natural. 

The results from our experiment regarding 'symmetry' show that facial symmetry affects the perceived attractiveness. However, the effect is rather small and by far not as influential as it has been reported in the media. To sum up our findings: Very asymmetric faces are judged rather unattractive, but very unattractive faces are not necessarily asymmetric. And vice versa : very symmetrical faces need not necessarily be judged attractive and very attractive faces often show deviations from perfect symmetry (see report!). Based on our results, symmetry only seems to be a rather weak indicator for attractiveness. Often it is even difficult to distinguish between the original and the perfectly symmetrical version, because irregularities in shape are rather insignificant. Therefore, the strong influence of symmetry that has been reported in the scientific literature over and over again is questionable.