I was sitting in the bathtub in 2008 when I thought of a simple way Johannes Vermeer (Girl with a Pearl Earring) might have painted his photorealistic pictures 350 years ago, long before the invention of photography. Vermeer's paintings are legendary for their realism, and many have speculated that he must have used some sort of optical technology, like the camera obscura, to get that result.
It's common knowledge that you can trace the images projected on the screen of a camera obscura, which is basically a black box with a lens mounted on one side. This helps you get the size and shapes of things established on the canvas. Intuitively it seems that you could paint colors right on the projected image and get a photoreal result.
In fact, this does not work. If you try it, you'll see why. The light projected by the lens obscures the color of the paint you are applying to the canvas. It makes the paint look too dark and too colorful. You must constantly turn on the light to see what color you have actually painted. There is simply no way to accurately compare the paint color to the projection. They interfere with each other.
Looking at Vermeer's paintings, it seemed to me that he must have had a way to not only trace the shapes, but capture the colors of a projected image. If he could do that, his paintings might be a form of photography, achieved not with film and chemicals, but with the human hand. Vermeer's paintings might be 350 year-old color photographs.
There are clues in Vermeer's paintings that he did this. For example, the white wall in the back of the room seen in The Music Lesson. [Click images to embiggen.]
The way Vermeer painted this wall is consistent with a photograph. It is not consistent with human vision. If you were standing in the room that Vermeer painted, you would see that wall as a pretty even shade of off-white. The retina in your eyeball does some image processing to minimize the effect of light and shadow. To your eye, the wall appears to have far less contrast than it actually has. And if you can't see it, you can't paint it. But Vermeer, unlike other painters, painted his walls the way a photographic camera would record it.
In my day job I work with video and computer graphics, and I am used to looking at images from a technical point of view. To my eye, Vermeer had done something humanly impossible, and that's what I was thinking about when I got my bathtub epiphany.
Here's the idea: A small mirror on a stick that lets you exactly match your paint colors to the colors of your subject.
I set up a simple experiment to test the idea. I don't know how to paint but in a few hours I was able to use the mirror to copy a black-and-white photo. This was my very first oil painting.