The Aha! Moment: A Scientist's Take on Creativity

10 Tricks with Optics

151 10 Tricks with Optics A ll modern visual technology depends on a simple optical illusion— that a rapid succession of visual “stills” gives the impression of a moving image. Many youngsters, including me, have explored this effect rather informally by drawing pictures on the corner of a book and then flicking through the book corner to see the moving image. Indeed, at the age of 10 or so, I graffitized the family telephone directories by drawing a simple pencil picture on the corner of each page, so as to draw a story. The Moving Image As so often, my creative friend David Andrews opened the field properly . He turned crude page flicking into a real mechanical art form. He drew a real cartoon film on a long paper strip. There was no projection system; you just looked at the paper tape as it jerked along. On the back of each frame he glued a cardboard strip for his “projector” to drive. Most commercial films use a film, a long sequence of transparent still frames held on a spool. It moves in front of a powerful lamp in a series of jerks (the screen rate, typically 24 frames per second). During its moments of stillness, the powerful lamp throws the image of the selected frame onto a viewing screen via a projection lens. That lens is adjusted to give the sharpest possible image; the whole thing is called a projector, and the audience sees the rapid sequence of projected stills as a moving image. David’s machine was much simpler; the film was opaque, drawn or indeed painted on the paper of the tape, and you looked at it directly. Each picture was a little pen-and-ink sketch painted with watercolors, 152 The Aha! Moment and the screen rate was about 12 frames a second. With his machine, each frame was still for half the time (during which the eye could see it) and was driven to the next frame for half the time (during which a black rotating shutter obscured the movement). I devised a slightly improved machine, in which the picture tape was still for three-quarters of the time and moved to the next frame in a quarter of the time. Both of us had to balance the need for optical continuity against the trouble of drawing hundreds of pictures. Each picture might only be 4.5 centimeters wide but still had to be carefully created. I drew mine with a magnifying glass and used a stencil to copy details from one frame to the next without too much jerking. My planned frame rate was about 11 frames a second. This gave a rather jerky but effective illusion of motion. The professional standard of 24 frames a second was adopted to let the film carry a soundtrack. European TV, which uses 25 frames a second, shows film a trifle fast. American TV, which delivers 30 frames per second, has a separate arrangement for transmitting film. My major artistic achievement was to invent “endless films” drawn as a closed loop. You could then show a drawn film continuously. The enormous agony of drawing all those pictures was compensated by seeing each of them many times. I had a lot of trouble devising a connection that would go through my viewing machine. My loop masterpiece was the “Gunpowder Powered Internal Combustion Engine,” 238 carefully drawn frames. Much later I transferred my animations to 16mm color film and thence to modern optical media. They still survive! The crude cartoons that David and I drew transmitted visual information at about 1 megabyte per second (fig. 10.1). Professional 16mm film transmits maybe 20 MB a second, 35mm film about 100 MB a second , and high-class IMAX film some 1,700 MB a second. And yet all this mighty optical machinery pays no attention to how our visual systems work. The eye does not perceive the whole scene. It concentrates on a tiny region that it scans around the scene. The brain then cobbles together a general visual impression.The human optic nerve is very narrow, and I guess that we can “see” only about 0.001 MB a second. We now know that the eye scans around a scene in sudden movements called “saccades,” during which the optical system is turned off. This brief “change blindness” lets you change the image. During a saccade , you can alter the color of a person’s hair or even erase him from...