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Gurney Journey | category: Visual Perception | (page 5 of 15)

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Gurney Journey

This daily weblog by Dinotopia creator James Gurney is for illustrators, plein-air painters, sketchers, comic artists, animators, art students, and writers. You'll find practical studio tips, insights into the making of the Dinotopia books, and first-hand reports from art schools and museums.

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Do skills at face recognition help you draw a better likeness?

Vision scientists from the University of Wellington wondered about the relationship between face-recognition skills and the ability to draw a convincing likeness.

Another related question: If you're not so great at recognizing faces, can you ever be any good as a portrait artist, even if you practice a lot?

A diverse group of participants were asked to draw a likeness based on a photo. The participants were also evaluated separately with various standard face recognition tasks.

Do skills at face recognition help you draw a better likeness?

The participants included those with some expertise (black frames) and novices at drawing (gray frames).

The drawings were ranked according to a numerical score that was given by judges who didn't know anything about the people who did the drawings. The drawings with the highest likeness scores are shown at the top of the chart. Not surprisingly, artists with practice at drawing got more recognizable results.

But the scientists wondered: what about the subjects who were novices at drawing? Presumably they would not have derived any advantage from training. Would those novices with better native face recognition abilities be more successful at drawing a likeness?

The answer is yes: there is a strong correlation: The ability to successfully recognize faces predicts how well a non-expert can capture a likeness in a drawn portrait.

Do skills at face recognition help you draw a better likeness?
Art by Chuck Close
What kind of training or method can help to overcome these deficits? I believe there are some art approaches: Notably the small shape-mapping technique used by Chuck Close, who has admitted to being face blind. I presume also that the skills taught in Bargue-based ateliers can help a person with poor face recognition abilities to produce effective likenesses.

Do skills at face recognition help you draw a better likeness?
Daumier
But what about caricature, which can't benefit from such methodical systems? To be an incisive caricaturist, or to paint "realistic" portraits with subtle exaggerations, do you need to have expert native skills or can training overcome deficits? I'd love to know the answer to that question.
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Scientific paper: "Face processing skills predict faithfulness of portraits drawn by novices."
Side note: National Gallery has cancelled a planned exhibition of Chuck Close due to concerns over allegations of sexual harassment
Video: Oliver Sachs talks about face blindness

Curvature Blindness Illusion


A series of paired lines passes through areas of white, grey, and black. The lines remain the same throughout. They have a consistent wavy (sinusoidal) shape. 

The difference between the sets is the placement of light and dark segments: one set has the tone change at the bottom of the curve.

Curvature Blindness Illusion
As the sets of lines pass through the grey area, some of them seem to take on an angular, zig-zag quality. The effect is extremely compelling.

Psychologist Kohske Takahashi of Chukyo University of Japan discovered the illusion. He suggests that when the brain's visual system is faced with ambiguous cues about whether it's seeing curved or straight-segmented lines, it favors the angular cues:

"The underlying mechanisms for the gentle curve perception and those of obtuse corner perception are competing with each other in an imbalanced way and the percepts of corner might be dominant in the visual system."
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More:
For a high level discussion, read the comments after the Discover Magazine blog post.
Thanks to several of you who let me know about this.

Pixelated Faces

Here are four photos of celebrities or politicians, greatly degraded by pixellation. 
Can you recognize any of them?

Pixelated Faces
Subject 1

Pixelated Faces
Subject 2
If you're having a hard time recognizing them so far, you might try making the displayed images smaller.  On a Mac, you can do that by pressing Command and - at the same time.

Pixelated Faces
Subject 3

Pixelated Faces
Subject 4
Ready for the answers? Here are higher resolution photos, together with the pixelated versions.

Pixelated FacesPixelated Faces
Leonardo Di Caprio

Pixelated FacesPixelated Faces
 Scarlett Johansson

Pixelated FacesPixelated Faces
Anne Hathaway

Pixelated FacesPixelated Faces
Vladimir Putin

If you recognized any of them from the pixellated version, consider how remarkable that is. The images are highly degraded, with no indication of the shapes of the features, just some brown squares where they eyes would be.

Pixelated Faces
Blurring is another way to reduce the information in a photo and to make it lower resolution. Can you recognize these faces? (Answers below in fine print.)

Individuals shown in order are: Michael Jordan, Woody Allen, Goldie Hawn, Bill Clinton, Tom Hanks, Saddam Hussein, Elvis Presley, Jay Leno, Dustin Hoffman, Prince Charles, Cher, and Richard Nixon. 

Recognizing faces out of such incomplete information is a formidable achievement, which tells us something about how we process visual information about faces. Scientists found that "about half of the observers were able to recognize a face of merely 7x10 pixels, and recognition performance reached ceiling level at a resolution of 19x27 pixels."

Researchers have drawn some conclusions from experiments like this:
• "Unlike current machine-based systems, human observers are able to handle significant degradations in face images."*
• "Pigmentation cues are at least as important as shape cues."
• "Fine featural details are not necessary to obtain good face recognition performance."
• "The ability to tolerate degradations increases with familiarity."  

Pixelated Faces
Detail of a painting by Frank Duveneck
As painters, this is a good reminder that the broad, simple, tonal lay-in stage is at least as important as the finicky details and the linear relationships that we obsess over. 

Here's a practice idea for students: If you can take a big paintbrush and accurately translate it into a few spots of tone, you're well on the way to painting good likenesses.

Studies Referenced:
—A. Yip and P. Sinha, B. Role of color in face recognition,[ Perception, vol. 31, pp. 995–1003, 2002.
—V. Bruce, Z. Henderson, K. Greenwood, P. J. B. Hancock, A. M. Burton, and P. I. Miller, B Verification of face identities from images captured on video,[ J. Experimental Psychol.: Applied, vol. 5–4, pp. 339–360, 1999. 
—V. Bruce, Face recognition in poor-quality video,[ Psychol. Sci., vol. 10, pp. 243–248, 1999.
* Machine learning systems are getting much better at recognizing people despite pixelation (see comments).

If you liked this topic, you'll love these previous posts

Cracking the Code of Face Recognition


Cracking the Code of Face Recognition

Scientists at Caltech have come to a better understanding of how the brain recognize faces. They already knew from brain imaging studies that certain brain regions are especially active during a face recognition task.

But what those regions do and how they interact with each other has remained a mystery. One recent theory had suggested that individual cells were associated with specific faces. But that idea may not explain how the faces were coded in the first place.

The outcome of this study, which used monkeys as subjects, suggests that as few as 200 localized neural areas specialize in specific aspects or vectors of the face, such as the spacing between the eyes or the height of the forehead.

Using thousands of computer-generated faces that could be constructed from such vectors, scientists showed monkeys a set of individual human faces. Then, using solely the electrical signals transmitted from the monkeys' brains, their colleagues were able to generate a predicted face based only on that abstract information. The scientists were surprised how close the predicted face matched the actual face.

The findings still need to be replicated, but they promise to help in the development of artificial facial recognition technology. They also have relevance for portrait artists. According to the New York Times, "the brain's face cells respond to the dimensions and features of a face in an elegantly simple, though abstract, way." Perhaps that would explain why caricatures so elegantly define an individual.

Articles:
New York Times
Scientific American 
Full text of scientific paper
Engadget

Venus Effect

The Venus Effect is a perceptual illusion based on classic paintings that show Venus supposedly admiring her own reflection in a mirror.

The viewer, seeing her face in the mirror, may naturally assume that Venus is looking at herself.
Venus Effect
Velázquez's Rokeby Venus
The effect gets its name from several old master paintings, including this one by Diego Velázquez.

Venus Effect
Veronese's Venus with a Mirror
If she were really looking at herself, we probably wouldn't see her face in the mirror at all (unless we were looking directly over her shoulder). 

Venus Effect

Titian's Venus with a Mirror is even more wildly off-angle.

Venus Effect
Peter Paul Rubens' Venus at the Mirror, c. 1614–15.
Given these eye lines, Miss Venus would have to be looking at us, the viewer. That's the way the Rubens looks to me. I read it as her looking at me as I accidentally break into her dressing room. But I think Rubens and his audience interpreted the painting as Venus looking at herself.

The Venus Effect also shows up in cinema, where an actor looks at their mirror reflection. Their head position and gaze direction are often "cheated" so that we can see their face in the mirror without also seeing the camera. 

Venus Effect on Wikipedia

Zograscope

Zograscopezograscope is an optical device designed to disrupt depth cues when looking at a flat picture and create the feeling that you're looking at a real scene.

It consists of a large lens held vertically in a frame, and attached to an angled mirror. The viewer looks through the lens at the mirror reflection of a picture laid out horizontally on a table.

The device interferes with stereoscopic cues, and it collimates the light, resulting in an impression that you're looking at a real scene.

Zograscope
Special perspective prints were manufactured to work optimally in these devices.



Zograscope

Other zograscopes were portable units made to look like a fake book when folded up.

Zograscope
Optical instruments like this were popular in the 18th century as a form of parlor entertainment.

I've seen similar devices, such as cabinet stereoscopes and peep boxes. One I saw recently had dual eyepieces with anamorphic images mounted on the inside of the box, which adds even more to the impression of virtual reality.
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Resources
• You can make your own zograscope with an inexpensive Fresnel lens (less than $10) mounted in a cardboard box.

• Book: A Companion to Early Cinema

• Read more online about zograscopes and perspective prints

• Wikipedia on Zograscope

Ouchi-Spillman Illusion

As you look at this black and white figure, move your head back and forth. 
You may notice that the circle seems to shift independently from the background.

Ouchi-Spillman Illusion
Ouchi-Spillman Illusion, Lothar Spillman
The apparent drifting or jumping in the design mirrors your eye movements and head movements as you peruse it. Scientists propose that: "Slow sliding movements may represent involuntary ocular drifts, while occasional jerks suggest a contribution by microsaccades."

Ouchi-Spillman Illusion
"Ouchi-Spillmann-Vasarely illusion"©Akiyoshi Kitaoka 2014 Via Op Art 11
Here's another variation of the illusion. To get the full effect, try picking up your computer or device and gently shake the display left and right. The sphere or disc in the center separates from the plane of the background and becomes dimensional.

Ouchi-Spillman Illusion
Rotating tilted lines illusion via CR Society
In this variation, the central circle and the ring around seem to shift and shimmer in relation to the background. 

Researchers have noticed that these effects diminishes with age. There's some debate about whether that fall-off is due to weaker eye movements or less robust perceptual abilities within the brain itself. 
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Do cultural factors influence how we look at faces?

Do cultural factors influence how we look at faces?
According to experimental findings reported on LiveScience, the way we look at faces is not entirely hard-wired, and may be influenced by cultural factors, which vary between the east and west.

One study suggests that when reading an expression of a person in a group photo, Westerners zero in on the individual, while East Asians pay more attention to reactions of the other members of the group. Lead researcher Takahiko Masuda, a psychology professor at the University of Alberta, says "East Asians seem to have a more holistic pattern of attention, perceiving people in terms of the relationships to others," while "People raised in the North American tradition often find it easy to isolate a person from [their] surroundings."

In another study, illustrated above, cognitive neuroscientists compared the eye tracking data of Western and East Asian observers who looked at faces on a computer screen. The results suggest that "Westerners tend to look at specific features on an individual's face such as the eyes and mouth whereas East Asian observers tend to focus on the nose or the centre of the face which allows a more general view of all the features."

The author of the article, Charles Q. Choi, suggested the conclusion that "Westerners often concentrate on individual details, while East Asians tend to focus on how details relate to each other."

I'm a little skeptical about these findings, partly because there may be factors other than cultural ones that greatly affect how we look at faces, such as professional training and media exposure. For example, the way artists look at things, based on our training and inclinations, may supercede East/West cultural predispositions (see previous blog post on that topic). Also, I don't think eye tracking data alone can be used accurately to assess the degree to which people look at things holistically, since eye tracking can only record the path of the fovea, or center of vision. We need experimental data that can indicate to what degree the attention is focused on one spot versus a wider view.

Source articles: 
Culture Affects How We Read Faces
Face Recognition Varies by Culture

Compressing faces

Can you recognize the faces below? (Answers at bottom of post). The faces are compressed so the width is only 25% of the original photo. 
Compressing faces
Source: Pawan Sinha, MIT
Many computer vision systems are premised on the idea of making absolute measurements within the face, the way we would carefully measure when drawing or painting from life.

Compressing faces
From Wired

But apparently the human visual system does not depend critically on exact measurements. Scientists have discovered recognition doesn't suffer much with proportionally distorted faces. As long as the measurements are proportional within a region or across a single dimension—that is, as long as the ratios are preserved—recognition performance isn't greatly affected. 

So what structural aspects of the face are the most important for recognizing faces? The researchers conclude: "It is possible then that human encoding of faces utilizes such ratios (we refer to them as iso-dimension ratios), and this might constitute a useful strategy for computer vision systems as well. "

Answers: Ronald Reagan, Jason Alexander, Prince Charles, George Bush, Robin Williams, Woody Allen 

Credits: 
G. J. Hole, P. A. George, K. Eaves, and A. Razek, B. Effects of geometric distortions
on face recognition performance, [Perception, vol. 31, no. 10, pp. 1221–1240, 2002.
Pawan Sinha, MIT
Do skills at face recognition help you draw a better likeness?Curvature Blindness IllusionPixelated FacesCracking the Code of Face RecognitionVenus EffectZograscopeOuchi-Spillman IllusionDo cultural factors influence how we look at faces?Compressing faces

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