Foveon sensors have been used in cameras sold under the Sigma, Polaroid and Toshiba brands. In contrast to sensors using a filter array such as the typical Bayer pattern, where each pixel records only one color, a Foveon sensor records blue, green, and red light intensity at different depths within the structure of each pixel. Thus, no demosaicing is necessary, resulting in somewhat higher effective resolution and an absence of color moiré patterns (although monochrome moiré may still appear). This is also supposed to make fast downsampling (needed e.g. for video) easier; this potential advantage of Foveon sensors wasn't fully realized in many commercially available cameras.
Quattro sensor features different pixel sizes in different layers