In this article we look at the Foveon X3 sensor, providing a guide to what it is for and how it works


Typical sensor photosites are dedicated to one primary colour, but Foveon photosites are sensitive to all three

The vast majority of colour digital cameras use a sensor based on a Bayer colour filter array, where individual photosites are dedicated to one of three primary colours, usually red, green or blue. A Foveon sensor and a Foveon X3 sensor are very different, as every sensor photosite is sensitive to all three colours. This fundamental difference means a lot but is widely misunderstood. Foveon X3 sensor is a technology now owned by the Sigma Corporation of Japan.

Camera resolution is, by convention, a count of the photosites on a sensor because this matches the so-called native resolution of that sensor. A Bayer filter sensor needs at least three photosites to record the full spectrum of colour, and because that information can’t be recorded at a single photosite location, you can’t represent a single pixel of full-colour image data precisely. Only a Foveon X3 sensor can do this. Because on a Bayer filter sensor colour information is recorded at a third or less of the photosite resolution, this information has to be interpolated and then basically an estimate of the colour is assigned to each photosite position and so to the image pixel represented.

A Foveon X3 sensor avoids undesirable artefacts that are a by-product of the colour interpolation process. A criticism of Foveon sensors is that they pretend to be higher in resolution than they actually are. But Foveon sensor resolution is the truth and Bayer filter sensors mislead. With those sensors the one-third colour resolution and the need for further processing means conventional sensor resolution is vastly over-stated.

It’s a shame that the virtues of the Foveon X3 sensor are enjoyed by such a small portion of the digital camera sector.