Sigma's Foveon Sensor: What It Is and How It Makes Megapixels Obsolete

...This unique way of measuring visible light -- taking photos -- utilizes a well-known phenomenon: different wavelengths of light penetrate silicon differently. Blue light, which has a short wavelength, doesn't penetrate very far, while green penetrates a bit further, and red penetrates the furthest. Foveon's sensor sandwiches three layers of silicon together, with different colors of light passing through each layer to reach the next. Blue light is measured the first layer, green on the second, and red on the last. The luminance values from all three are then combined to create an RGB pixel value.