Edges and Edge Detection Part 1: Neurology

Well, it's been too long since I've developed an idea that struck me while reading Margaret Livingstone's Vision and Art: The Biology of Seeing. But I've been mulling over the concept of edges, from which the concept of line arises. This is one of the fundamental tools of art, and well worth thinking about a little more.

How do we see edges? As always, the brain avoids using high-level structures for brute information processing of the visual field. You might think, well, receptor cells in the eye respond to light, firing a signal when they are exposed to light and failing to fire a signal when they are exposed to darkness:


That's what you would think, my friend, but you would be leaving most of the story woefully untold. Yes, these cells exist. But it seems that this fairly obvious scheme is not cool enough for the brain. So the raw "light/dark" cells feed this information, while in the eye, to ganglion cells that show center/surround signal processing. Instead of a binary ON for "I'm lit" and a binary OFF for "I'm not lit," they respond to their little flock of receptor cells to produce a continuum of signals (actually, a continuum of frequencies of firing). The simplest scenarios are as follows. The bottom two "high frequency" responses represent, I'm pretty sure, the optimum firing conditions for two different types of center/surround cell, both of which show the first two responses in totally lit and totally unlit conditions:



Keep in mind that we're talking about black and white processing here. We'll get back to that.

But consider this scenario:


That's a classic edge - a sharp contrast over a short region. And the cell is equipped to produce a signal frequency between "medium frequency" and "high frequency" in response.

How does the brain take advantage of all this fancy information that's getting processed in the eye? Well, a couple of Livingstone's colleagues in the Department of Extreme Cleverness, David Hubel and Torsten Wiesel, figured out that these center/surround ganglion cells are feeding their information to cells in the brain that are equipped to compare signals from adjacent ganglion cells. And these higher-level processors show orientation. Several different specialized cells, which are at the point of detecting edges, are wired to each cluster of lower-level center/surround cells, and they fire when the cluster, as a composite, matches their specialized detection function:
On the left are the center/surround ganglia. On the right are the edge detector cells in the brain. Shaded cells are busy firing.

From there, you're off to the races. Further specialization and processing allows detection of continuous edges, broken edges, curved edges, corners, etc. And finally, you have an image that you're conscious of.

What's important to take away here is that, even though you are not aware of it, deeply embedded in your visual perception of the world are these low-level edge data, which are cognitively close to line data. Lines are deeply embedded in your sense of sight. This is a big part of the reason that when you see a line drawing...


...you see a comprehensible visual field, even though virtually all of what you intuitively think of as information in the visual field is missing. The defining characteristics of a critical part of that visual field are present.

This is also why the figure/ground distinction exists in reality even though it does not exist in the raw visual field. The brain never sees the raw visual field. It only becomes aware of the neurologically-processed visual field, into which the edge phenomenon has been encoded.

Now, lots of interesting artistic results arise from all this, and the next few posts will build up a discussion of it. For the time being, let me just say, the same center/edge processing exists in color, but it's lower resolution. This is a big part of the reason that Degas died thinking of himself as a failure. His grand project was to unite the artistic phenomena of color and line. He never thought he found that unity, despite his gorgeous attempts:


Why? Because the line he intuitively recognized as Line is achromatic. It cannot be unified with color. Which is not to say that Degas's attempt was a waste of time. Just look at what he accomplished by pursuing an impossible goal.

A couple notes:

1. Doing all those diagrams in Photoshop? Total pain. Not recommended.
2. I think I'm screwing up the real model of processing as presented by Livingstone. The thematic fundamentals are correct, but I can't vouch for my having related every step of the way correctly. Just read her book, it's awesome.

Holy Moly I'm Bad At That

I forgot to mention - the February/March issue of International Artist is on newsstands, and it's got the first of my four articles on working with models. The publisher did a beautiful job on layout and reproduction, showcasing this painting, this one, and a few I'm working on now. So run out and buy a copy! Or a painting...

As long as I've got your attention, let me post a couple drawings of Piera from yesterday. This continues my try-new-ideas project. My new idea this time was to use white and red pencil on rough black paper.

Well, new idea for me; other people have actually thought of doing this before.

What was interesting about the experience was that you basically can't erase and can't put down preparatory marks that aren't prominent in the final piece. So it reduces to the same situation as working in pen: you live with your mistakes, and you make your mistakes a virtue. I thought the draughtsmanship turned out a little cruder than usual, but this, combined with the tendency of the medium toward having a really nice sense of mass, gave the efforts a sense of emotional solidity which I found very satisfying. Your mileage may vary.

We're not computers, Sebastian. We're physical.

One of Rutger Hauer's startling number of immortal lines in Blade Runner.


I remembered it the other day while chatting with Adam Miller. He was talking about the surprising feel for painting he encounters sometimes when teaching older women. It wasn't a generalized feel for painting; it was a rapid understanding of how to handle the problem of getting paint onto canvas well.

He speculated that the demographic-specific aptitude results from the physicality of painting. Which is to say, you need to be sensitive to a physical process that you execute through dexterity of the hand. The older women tended to have experience with cooking, mending, and crafts. They had muscle memory of subtly shaping materials by hand in service to an idea.

This quality of painting is easy to forget. The casual viewer can easily confuse figurative painting with photography - not so much thinking that they look the same, but that they arise from similarly vague or abstract procedures. This is not so.

Paint must be coaxed onto a canvas. You can do it rapidly or slowly, thickly or thinly. But you cannot do it automatically. You have to figure out the physical properties of the highly viscous fluid and how it interacts with brush and surface.

Because I hate schooling, I figured it out on my own. I would take a pad of primed canvas sheets, some brushes, and tubes of white and burnt sienna with me to life drawing twice a week from 2001 to 2004. It often struck me as ridiculous, trying to make an image in an archaic way, by shoving colored substances around on a surface. Once I stopped shoving, I started getting it right. It took me those three years to learn the rudiments of the sensitivity and dexterity of hand, and to be able to guess what paint would do as I applied it to the surface.

Then I had to learn the properties of the colors. I spent a few months on cadmium red. French ultramarine. Burnt umber. Yellow ochre. Not just the way they mix, or their relative strengths - but their characteristic consistencies. How to move them around on the surface until they went where I wanted, as I wanted. When my friend James realized that paint is not the same as the photographic emulsion, which takes care of all that color business, he was shocked - it sounded like alchemy to him.

By nature, I do not particularly like to draw attention to the physical substrate of the image. This attitude isn't right or wrong - Steve Wright is producing amazing work from the opposite perspective: he likes you to know that the paint is physical.


His paint is dazzlingly thick, and the brushstrokes are clear and distinct. My own paint is nearly as thin as watercolor, and you can rarely see a brushstroke. Both processes, however, result from a process of learning, not only to see, and interpret, and make aesthetic decisions, but to pour the outcome of all of that into a physical process that feeds back into the more abstract functions and informs them as well.

When I screw up, I still sometimes instinctively crab my hand to hit Apple-Z. But it's not there; paint is physical.

Against Authenticity

"Authenticity" is a fairly generally-lauded value in art making. I have philosophical and personal reasons to oppose it. The philosophical ones very likely arise from the personal ones, as a means of self-justification, or simply because I have a surprising and specific experience with authenticity. So let me explain the personal issue first.

Everybody has a natural line. This could also be called an authentic line. It is the line that spontaneously emerges as the most uncensored line an artist can produce in the freest, fastest drawing they can do. Some artists have extremely distinctive and recognizable natural lines. Egon Schiele comes to mind, with his knobby junctures and jagged delineation of edge:


So does Domenico Tiepolo, with his bewitchingly weird wobbliness:


Others you might want to think about are Albrecht Durer, with his tense, cramped line:


...and Boticelli, with his graceful, sweeping line:


I think that, whatever modifications these artists have imposed on their natural line, a sense of their natural line comes through. These artists are in the marvelous position of having natural lines which are original and pleasing - their authenticity of expression is extremely delightful and, moreover, contributes to a new understanding of the capabilities of art.

I have a natural line, an authentic line, as well. I've had this line since I was five or six years old. I'm pretty convinced there's a genetic basis for it, and for all natural line. But there's a severe problem with mine - somebody else took it first.

The drawings of mine below are from a drawing session with Piera on December 30, 2009. She's pregnant, and can't work around oil paints and their associated toxins right now, so I'm doing a bunch of drawings and watercolors and whatnot, just playing around and experimenting, until she has her baby. I decided to do some drawings using my natural line; over the course of an hour, I drew 12.

Here's one of the drawings from that session:


And here's one that's too similar for comfort:



Yes, that's Henri Matisse.

The resemblance is not precise, but it's close enough that my authentic line looks derivative. And let me add that there are few things more fun for me than using my authentic line. Let's look at a few more drawings:


Moi.

Henri.

I should point out that I wasn't copying the Matisse drawings I'm including here - I found these post facto with a google search.


Aussi moi.

Aussi Henri.

Well, that's a bummer, isn't it! My authentic line looks completely inauthentic - it looks like an accomplished put-on.

Oh well. Here's how I dealt with the problem: when I was first becoming self-aware as an artist, this whole idea of authenticity didn't really exist in my universe. I just thought I was drawing badly! Because what I wanted was to draw a much more detailed, proportional, and harmonious image. I wanted to draw like Da Vinci. And I spent, what, ten or fifteen years figuring out how to draw? So now I have a way that I tend to draw which I also like very much:


It's not Da Vinci, but what is? I retraced the steps that Da Vinci took to learn to draw - life drawing and anatomical dissection, and above all, constant practice. So I think of it as time well spent.

That's my personal problem with the concept of authenticity.

Let me expand the argument to a general problem with the concept of authenticity. To do that, let's take a brief look at the justification that authenticity-proponents offer for its value.

The stated link between authenticity and merit is that art, being an emotionally expressive medium, is at its best when the line between impulse and work is as short as possible. The premise is that all people have something worthwhile to express. When that expression is unmediated, a true form emerges - an authentic form.

The unstated link between authenticity and merit is that it provides an algorithmic method for determining what we think of art. If an artist from Pasadena paints suburbs - that's authentic. If an artist from Ghana paints traditional tribal patterns - that's authentic. A simple comparison of the biography of the artist with the content and style of the art provides a linear metric for quality.

As far as I can tell, these are the two major arguments for authenticity. Let me attack the second argument first.

This algorithmic method of determining the "validity," and hence the "quality," of art, is yet another attempt to avoid the fundamental problem with forming an opinion of art. What is required in forming an opinion is taste. Developing taste and taking the responsibility for assertions of taste are insanely difficult and potentially humiliating tasks. People like to be told what to think of things. At its simplest, the biographical-authenticity argument is a quick method for providing an opinion without forcing the viewer to come to his or her own conclusion. It appeals to the fear we all have when looking at unknown art and asking ourselves, "Should I like it?"

It is also attended by a host of post-modernist argumentation. All of this argumentation revolves around a specific form of the general dehumanizing intent of post-modernism. The specific form is the denial of the human capacity for imagination. Which is to say, the post-modern argument is that any expression that does not arise directly from and address directly the personal (or, more particularly, demographic-ethnic) experience of the artist is inauthentic and hence, for various reasons, invalid. Anybody who denies the validity of imagination consequently denies the ability of art to communicate, and therefore is not only wrong, but has no pertinence to my project.

The first argument, the stated one about shortening the link between emotion and expression, is more interesting. Yes, art is emotionally expressive. Yes, true emotion is absolutely fundamental to sincere art. Yes, sincere art is the basis for good art. And yet - I cannot buy the Romantic overtone of the argument. Let me turn to Wordsworth's famous preface to the lyrical ballads. Famous? you say. I've never heard of it.

Sure you have. Here's the famous part:

For all good poetry is the spontaneous overflow of powerful feelings...

Here's the not-so-famous follow-up. Well, he has two follow-ups in two different parts of the preface. The second is better known:

...it takes its origin from emotion recollected in tranquillity

The first is more complete:

...and though this be true, Poems to which any value can be attached were never produced on any variety of subjects but by a man who, being possessed of more than usual organic sensibility, had also thought long and deeply. For our continued influxes of feeling are modified and directed by our thoughts, which are indeed the representatives of all our past feelings; and, as by contemplating the relation of these general representatives to each other, we discover what is really important to men, so, by the repetition and continuance of this act, our feelings will be connected with important subjects, till at length, if we be originally possessed of much sensibility, such habits of mind will be produced, that, by obeying blindly and mechanically the impulses of those habits, we shall describe objects, and utter sentiments, of such a nature, and in such connexion with each other, that the understanding of the Reader must necessarily be in some degree enlightened, and his affections strengthened and purified.

Whoa! Now there is a strong argument for artifice.

I am reminded of two other comments on the subject - somewhere (I can't remember where), Nietzsche denigrates art as a sort of second-hand emotionalism, because anyone who felt a real first-hand emotion would be able to do nothing more than scream. Or something like that.

And Proust, in the final chapters of his book, concludes that his writing involves the transmogrification of the raw material of memory into a kind of artistic form or image which redeems and reclaims the lost past, fixing it and allowing, not the past, but the art, to be possessed. Hence the name of the volume, Le Temps retrouvé, generally translated as Time Regained.

What this means for the practical artist is that the locus of necessary authenticity lies not in method, but in source. Successful authentic method - that is, originality of method in addition to emotional or cognitive authenticity of the method - is, like love, nice work if you can get it. But it's a crapshoot of genetics and art history if you can get that kind of work. So it is good to remember that art, methodologically, is artifice. Art is making one thing, generally pigments mixed with a medium of some sort, look like something else, generally (in my case) naked ladies. So it's good not to get too hung up on authenticity of method, since the materials by means of which the method is executed are totally false to begin with.

The title of this post is a little bit of a falsely provocative choice. Of course I believe in authenticity. But the place where I believe authenticity is most important (and remember, after all, I have to) is in the inspiration and vision which the method serves. Find some true thing that you must transmit from yourself into the world, and use whatever works to give it a body.

Since I started writing this post, I've worked with Piera some more. I figured that since I can't help the Matisse effect, I might as well steal his best tricks. In the pieces below, I've drawn on top of colored-paper cutouts glued onto heavy white watercolor paper.





P.S. I apologize for hitting "post" before finishing uploading images. My bad. Fixed now.

We have guests!

Well, Pengo, Chris, April, Greg - we've got some guests today. My work is posted right now at www.artistaday.com, and this seems to be driving 1.2 metric buttloads of traffic to my site, and a little overflow to here. So our cozy little conversation about art and artists is much more public today. Welcome, guests, and I hope you enjoy! And longtime readers - I apologize again for not posting more. It takes a lot of thought to cook these things up! But I've got a few things to tell you in the next several days, especially about my problematic relationship with Matisse. More soon.

Oh, and here's a painting I finished yesterday. As usual, the background took forever to get around to. The figure and the first layer of the background were finished by September.