Thursday, October 29, 2009

Optical Black: Part 1

I don't have time to write about this entire topic today, and I'm pretty sure you don't have time to read about the whole topic, but I'm going to get started on the perception of darkness.

A lot of what I have to tell you is my take on the fascinating ideas discussed in Vision and Art: The Biology of Seeing, by Margaret Livingstone. If you're an artist, run, don't walk, to buy and read this book. And don't give me any lip about how artists aren't analytic thinkers, and all the science talk in the book is wigging you out. This book is easy to read, beautifully illustrated, and almost insanely useful. Besides, I think that stuff about how artists are beautiful, chaotic retards is mostly hype. Rubens managed a perfectly satisfactory career as a diplomat while being an amazing painter and all-around stud:

I negotiated the peace between Philip IV of Spain and Charles I of England. What have you done lately?

Point being, good book, don't worry, you'll understand it.

Now, we're talking about how we perceive darkness. The "naive" form of the argument is that darkness is essentially "+ black," right? Just a lack of light. It turns out that's true, but that's only one of the ways we perceive darkness. The other one has to do with the different ways the human eye responds to light of different colors. Take a gander at this:

It's simplified somewhat from the true state of things, but that's a spectral response curve for the daylight sensory neurons (the cones) in the human eye. A spectrum of actual colors is helpfully provided at the bottom. What does this graph mean? It means that at normal daylight brightness levels, the human eye is most sensitive to light at a wavelength of about 545 nanometers - a greenish color. But look at that drop-off on either side of it! That is one hell of a drop-off, would you not say? I would say that it is, indeed, one hell of a drop-off.

What that hell of a drop-off means is that if you have equally bright violet and green lightbulbs shining on equally white sugarcubes, the violet-lit sugarcube is going to look pretty damn dark compared to the green-lit sugarcube. Even though they have the same intensity of light energy falling on them!

Well, that's very interesting. That means there are two ways that we can perceive darkness. One is the intuitively obvious "+ black" means. The other is by means of the color of the object perceived. A blue object is just going to look darker than a yellow object. Even fairly similar colors are going to look different in luminosity. Orange is going to look brighter than brick red.

Harold Speed, writing in the 1920's, had no idea about the scientific awesomeness underlying the difference between these two forms of darkness. But he pegged it anyway in his history of the development of art. He notes that in the Renaissance and Baroque periods, the representation of form through chiaroscuro was developed to a high degree of verisimilitude, but that this technique relied essentially on "+ black" (or "+ brown") to show darkness:

The bright-dark distinctions between colors themselves do not functionally enter into the paradigm until the Impressionists (and, I might add, the contemporaneous Academics):

Seurat blinked in the sudden illumination and said, "It's you - my archenemy, William Adolphe Bouguereau!"

Bouguereau twirled his moustache and replied, "You see, Georges, you and I are not so different after all."

It's true. Under all the differences in brushwork and theme and virtually everything else, both of these 19th-century movements partake of a single revolution in the understanding of how the eye perceives darkness and light, shifting from the fundamentally monochromatic luminosity model of the 18th century to a modern panchromatic model. The panchromatic model is often referred to by the shorthand of "blue shadows," because painters in this school tend to paint blue shadows on figures lit by daylight (since the shadow side is keyed to reflected light from the blue sky). Before the 19th century, those shadows were almost always painted in brown or black. Yes, blue for shadows - not only the "actual" color seen in nature, but a color the eye sees as dark.

A split occurred once the dust had settled. Among notable 20th century painters named Henry, for instance, you'll find Henry Moore on the monochromatic side and Henri Matisse on the panchromatic side.

Why must there be a split? This is very interesting. It's because these two methods of seeing dark - "+ black" and "dark color" - correspond with two different visual-processing systems in the brain. The "+ black" system is much older, evolutionarily speaking, than the "dark color" system (I told you Livingstone's book was awesome!), and people tend to favor one or the other.

There is no grand unification of aesthetics, because the underlying cognitive process is itself dichotomous. All unifications tend to split under the strain of sustained examination.

Enough for now. More on the aesthetic, practical, and spiritual implications of all this sometime soon.


  1. Here's a question:

    How much of the shift from monochromatic black to the era of "blue shadows" came as a result of painters having more time and resources at their disposal? I'm not a painter myself, but it seems that the Carravagio is like 50% black, so the painter really had to focus most of his attention on the other 50% while he could go easier on the black 50% since the human eye wasn't going to register much of that anyway. In other words, he painted half a picture and half black canvas. Was there any necessity in this?

    I'm reminded of something a cinematographer once told me, that lighting for film noir is the easiest form of lighting. With so much dark, there's so much of the set you can ignore since no one is going to see it anyway.

  2. Chris -

    This is true for cinematography, but not as true for painting. It certainly saves a little time to paint large areas black instead of filling them in, but in my experience, not so much time as to be worth altering your entire aesthetic to accomplish it. Remember, those areas are not the foci of the compositions, so most artists wouldn't be lavishing a ton of detail on them anyway, because it would be distracting from the point of the painting. Carravagio's black fields are, to my eye, an excited response to having discovered the mechanism of producing a cognitively convincing three-dimensional picture space, combined with an eye for drama. And yes, perhaps a little laziness - but without his blacks, he can't have his stark scenes, and the stark scenes are above all what drives him.

    A lot of painting goes a lot faster than you would think.

    As for the shift to the panchromatic model, I've read everything from that it resulted from moving the easel outdoors and painting under daylight, to a more scientific approach to sight based in the advances in optics of the 19th century, to the shift of key artistic players out of the classical training system and into a more autodidactic mode. I'm not convinced by any of these explanations, but it's a topic I don't know well, so I will also gladly admit ignorance.