The Land Effect
(Note: I've added a demo. If you have previously perused this page, you can cut to the crash by clicking here.)
In 1959, Scientific American magazine published an article by Edwin H. Land that upset the conventional wisdom about color vision. The article claimed that it was possible to produce a full-color image with only two component colors in place of the usual three. Land's claims were not widely accepted at the time, and they are still viewed with skepticism by many people.
Land was attempting to recreate some experiments James Clerk Maxwell performed in the Nineteenth Century using red, green, and blue filters. Three slide projectors were set up to superimpose black-and-white slides of the same scene photographed and projected through red, green, and blue filters.
During the process, Land inserted the filters one at a time. As soon as he inserted the first filter, he saw a full range of colors on the screen. He found that he could obtain a full-color image with just two projectors, one with white light and one with red.
Here are some pictures that illustrate the steps of the experiment, starting with an assortment of colored objects.
Below are two black-and-white photos of the objects, one taken through a red filter and one through a green filter.
The next step is to put a red filter on one of the black-and-white photos.
When these two images are superimposed, the picture at the left is not what you see. I've shown it here to emphasize how suprising the real picture— shown below— actually is. Even though the image is heavily weighted toward the red, one of the pens looks distinctly bluish. What's even more surprising to me is the hint of yellow on the top roll of tape.
The effect works better when the limited color image is all you see. Clicking here shows a demo of the same image with different backgrounds. If you suspect that the two images in the demo window are not the same, you should note that it takes about half a second for the difference to appear — the effect is in the perception, not in the image.
To prove that I'm not cheating, here's the same picture with a few sample colors expanded. As you can see, they're all shades of red or gray—there is no actual blue present. The gray areas look blue by comparison with the reddish cast in the rest of the image. (I can't explain the area that looks yellowish.)
Several sites on the world-wide web include information about Land's color experiments. For example, here's a link to one that reproduces some the photos from the original 1959 article. (As far as I can tell, the article itself is not available.)
The pictures above provide only a shadow of what Land actually saw using his projectors. In the Scientific American article, several illustrations were (admittedly) modified to make the images look as they did to the people present. With that idea in mind, here's a picture I've adjusted* to give you an idea of what a projected version of the red-white experiment might actually look like. You can see that it does not reproduce the colors in the original, but it may give you some idea why Land got so excited when he first performed the experiment.
What Land demonstrated was something color film photographers were already aware of: the ability of the human visual system to compensate for the color of the light source. Land's experiments clearly show the inadequacy of the conventional idea that the proportions of red, green, and blue light determine the perceived color. In actual scenes, the perceived color of each region also depends on the colors of its neighbors and the overall color of the scene.
*Is "Photoshop" a verb? Will I get sued if I don't mention Adobe?
Last updated on 11/9/2013
Copyright © Allen Watson III