Foveon sensor is composed of three Red/blue/green layers, so each pixels know exactly its color, while the Bayer sensor used by other manufacturers is composed of pixels that are either red, blue or green, and that implies some reading out of its color and its neighbour's one... and some glitches (typically moire or purple fringes). In order to reduce those, a Low-pass filter that blurs the picture a little bit is added on top of the sensor. Therefore, foveon pictures are way sharper, with true colors. This is the theory for colors... in fact it's a very hard to tame sensor and results can be very random. Plus the cameras are very slow because they have to process 3x more information. Sigma being a very very small company versus the other big guys, their R&D is limited. Still, it's a very nice camera to use for geeks who takes time to understand it. You hate it or love it. No in-between.