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Just how simple can a portrait be?

Some artist's portraits take the face down to its basic elements and this got us thinking.  Just how simple can a portrait actually be before one stops recognizing the person – in fact, how is it that we recognize faces at all?

Three recent papers on the subject have revealed some very interesting discoveries.

Simple Illustration Style Portrait

1) Natural ‘Barcodes' Help Us Recognize Faces

According to a study from UCL Institute of Ophthalmology, our faces contain ‘barcodes' of information which help us recognise people

Faces are unique in their ability to convey a vast range of information about people, including their gender, age, and mood. For social animals, such as humans, the ability to locate a face is important as this is where we pick up many of our cues for social interactions.

While recognising a person's face is a complex process, the first steps to processing visual information in the brain are thought to be more basic and to rely on the orientation of features such as lines.

By manipulating images of the faces of celebrities such as Coldplay's Chris Martin and actor George Clooney, researchers showed that nearly all the information we need to recognise faces is contained in horizontal lines, such as the line of the eyebrows, the eyes and the lips. Further analysis revealed that these features could be simplified into black and white lines of information – in other words, barcodes.

"Exposed skin on our forehead and cheeks tends to be shiny whilst our eyebrows and lips and the shadows cast in the eye sockets and under the nose tend to be darker," said Dr Dakin, the study's co-authour. "The resulting horizontal stripes of information are reminiscent of a supermarket barcode."

Supermarket barcodes were developed as an efficient way of providing information: straight, one-dimensional lines are far easier to process than two-dimensional characters such as numbers. In a similar way, our faces may have evolved to allow us to convey effectively the information needed to recognise them.

The researchers analysed various natural images, such as flowers and landscapes, and found that faces are unique in conveying all their useful information in horizontal stripes. The barcode pattern has many advantages: it can be recognised efficiently by the visual parts of the brain; is easy to locate in complex scenes; and appears to be resistant to changes in the overall appearance of the face.

The research may also help explain our ability to see faces where they do not exist, for example in clouds or in flames.

"Our faces are fairly symmetrical, and it is this symmetry that creates horizontal patterns," explains Dr Dakin. "Local symmetry can occur in natural phenomena, such as fire, and it could be that our brains recognise a barcode when a face isn't really there."

Our faces contain 'barcodes' of information which help us recognise people. (Credit: Image courtesy of University College London)

Research: Co-authored by Dr Steven Dakin of the UCL Institute of Ophthalmology published April 4 2009 in the Journal of Vision,

2) Two fixation points are needed for face recognition

Previous studies had indicated that during face recognition, we look most often at the eyes, nose and mouth, and a new study has pinpointed exactly where our eyes land when we see a face.

The researchers found this out by showing volunteers frontal-view images of faces, one at a time, and recording their eye movements with an eye tracker. The researchers were able to measure fixation points when the faces were shown (i.e. where on the face the volunteers looked).

In addition, the researchers limited the number of fixations that volunteers could make when looking at the faces to one, two, three or an unlimited number, by replacing the face with an average of all of the faces in the study when the number of fixations exceeded the limit. This is done while the eyes are "in flight" to the next fixation – when we are virtually blind until we land at the next spot.

The results, reported in the October issue of Psychological Science, a journal of the Association for Psychological Science, showed that during face recognition, the first two places we look at are around the nose, with the first fixation point being slightly to the left of the nose. This was surprising, as previous research has suggested that the eyes may be the critical point for face perception. In this study, it was not until the third fixation that participants looked at the eyes.

The researchers also found that two fixations are optimal for face recognition. Given the same amount of time to view each face, the volunteers performed better when they were allowed to make a second fixation than when they could look at only one fixation.

The authors noted, "This suggests that the second fixation has functional significance: to obtain more information from a different location."

The authors conclude that the nose "may be the ‘center of the information', where the information is balanced in all directions, or the optimal viewing position for face recognition."

When asked to determine if the face that test subjects were looking at was one that they had just seen a few minutes prior, test subjects first "fixed" their eyes near the centre of the nose, and when they moved their eyes to the second location on the face, it too was usually near the center of the nose. (Credit: Psychological Science, a journal of the Association for Psychological Science)

Research: Cognitive Scientists Janet Hui-wen Hsiao and Garrison Cottrell from the Temporal Dynamics of Learning Center at the University of California, San Diego

3) The eyes are key to recognising a face

According to a study from a researcher at the University of Barcelona, our brain extracts important information for face recognition principally from the eyes, and secondly from the mouth and nose.

Imagine a photograph showing your friend's face. Although you might think that every single detail in his face matters to recognize him, numerous experiments have shown that the brain prefers a rather coarse resolution instead, irrespective of the distance at which a face is seen.

Until now, the reason for this was unclear. By analyzing 868 male and 868 female face images, the new study may explain why.

The results indicate that the most useful information is obtained from the images if their size is around 30 x 30 pixels. Moreover, images of eyes give the least "noisy" result (meaning that they convey more reliable information to the brain compared to images of the mouth and nose), suggesting that face recognition mechanisms in the brain are specialized to the eyes.

Oil painting by YouAreArt.co.uk
Our brain extracts important information for face recognition principally from the eyes.

Research: Keil et al. "I Look in Your Eyes, Honey": Internal Face Features Induce Spatial Frequency Preference for Human Face Processing.

 

Our experience with our Simple Illustration style portraits is that to get the portrait to look like the person, the face shape also plays a very important part.

The relative position of the eyes, nose and mouth remains static, based on the photo, but we often manipulate the shape of the face in line with the client's wishes.
This would fit in with the research outlined above – if the key areas of eyes, nose and mouth are in the correct relative positions, then the shape of the face can be seen as more fluid.
We can thin the face to flatter, or simply change it to get more of a ‘sense' of the person than the photo we are working from can give us.

This article references several articles published on sciencedaily.com

About the Author

Sky Siljeg September 08