Foveon Inc. is the Californian company that manufactures Foveon X3 sensor for digital professionals cameras as the Sigma SD10 of Sigma Corporation, technically compound number as F7X3-C9110 X3

Foveon Sensor captures light being based on the fact that the waves of blue light are shorter than the green light and that these, are shorter than the red light. It uses a similar mechanics of the analog film. Three layers of sensors are arranged, a blue one that captures the blue light, an intermediate one green that captures the green one and a red one to capture the red light, in this order and from top to bottom, if the camera points up ceiling. See the figure below

It is necessary to keep in mind that Foveon captures 100% of each blue, green and red color, while the mosaic Bayer, commonly employee in CCDs and CMOS only capture 25% of the blue, 25% of the red one and 50% of the green, when keeping in mind that the human eye is more sensitive to the green color. See:

We can say about Foveon that, in theory, captures a true color, without having to depend on the interpolation technique to form an image, neither filters of any type to mask the imperfections of the technology. In addition, it must improve the CCD and CMOS in the color gradation and that is, let us say, the pending duty of the digital cameras, and it is superb on any analog good film. We should, also to recognize that the digital technology is almost perfect in the radical contrasts, that is to say, the edges. That is another story.

The issue to think about is the measurement, for Sigma, of the images size. If in the Bayer mosaic the space distribution is counted in long by width equal to quantity of pixels, Sigma includes the factor depth, that is to say, for three layers, to add to the equation. For example, the Sigma SD14 produces a native RAW image of 13,3 million pixels, following its specification sheet, what corresponds 2268 x 1512 x 3 pixels, in file size. The only bad thing, and it is a personal thought, is that you can not use, nowadays, beyond 640 ISO due to noise, and its poor performance with low light.