Thursday, August 02, 2007

Rembrandt, Magic And Retinex

Many, many artists before and after Rembrandt used heavy chiaroscuro—effects of shadow and light—for dramatic purposes. No artist before or after Rembrandt, however, used shadow as intimately as did Rembrandt, used light as idiosyncratically or to such profound effect.

Other artists use light and shadow, one might say, sensibly. Bright light, bright colors call attention to this or that aspect of an image. Dark shadows create recession, depth and engulf areas which might be distracting.

Rembrandt often reverse such thinking. The brightest part of a Rembrandt painting might be lighting shining on somebody’s shirt cuff to the side of the composition. Shadows often engulf the actual features of a person’s face, the very subject of the painting is typically half-lost in darkness. An image of grays and browns might appear sparkling with colors only to be seen upon examination to have just one or two patches of pure color. Yet the overall effect of a Rembrandt image is often so powerful a viewer gets the impression that Rembrandt has somehow magically reversed cause-and-effect, a viewer gets the impression that Rembrandt has somehow twisted painting techniques which should confuse an image and forced those techniques somehow to actually clarify the image.

I used to suspect Rembrandt belonged to some painters’ guild which passed along secrets of image manipulation from generation to generation. Reading a book like “Secret Knowledge,” by artist David Hockney made such a suspicion seem plausible. Many secrets of art technique have been lost because painters hesitated to write down or share their methods—after all, there was simple commerce at stake: if other painters could duplicate a painter’s images, they could compete for the same sales, the same patrons.

I discounted this conspiracy-oriented thinking, however, because although painters before and after Rembrandt have made use of chiaroscuro, no painter, not even Rembrandt’s most skilled students, ever used chiaroscuro in the same oddball manner as Rembrandt.

I now believe that Rembrandt worked the way he did because he had a deep, intuitive empathy for what laymen in the modern world call the Retinex theory of vision, what cognitive scientists call the constructive nature of vision.

Edwin Land, the inventor of the Polaroid process of instant photography, was one day doing an experiment that involved projecting images onto a white screen. Some images were black and white, some were full color and some had been photographed through special filters which only imaged certain wave lengths. Land noticed that when certain combinations of single-color images were displayed he perceived the images as appearing in full color. That is, human vision “saw” colors in certain images that laboratory instruments would completely fail to meausre.

Land did further experiments and eventually concluded that normal human vision involves not just the retina reacting to light but also the cortex of the brain somehow processing impulses from the retina. Land combined “retina” and “cortex” and created his “Retinex” theory of vision.

Retinex has become more of a curiosity than an on-going field of study. The amazing musician Wendy Carlos has experimented with Retinex for many years. There are websites here and there which discuss Land’s work.

But mainstream science seldom uses the phrase, and I think there are two reasons. First of all, it turns out that long before Land became interested in vision, philosophers speculated about how the brain may play a very active part in what we see. Secondly, cognitive scientists who study vision have discovered that the effects Land observed are only tiny aspects of a vastly larger system of visual constructions.

The human visual system constructs not just colors but also lines, areas of light and shadow, surfaces and complex forms themselves. Everything we see, in fact, is a construction in our brain.

And that’s just the beginning!

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