Back in 2006, Sigma's DP-series was well received for its imaging quality and fitting an APS-C sized Foveon X3 sensor into a small body, putting it high-up on the list of photographers looking for a camera in a very small niche. Sigma is relaunching the fixed-lens/fixed-length DP-series of cameras, with the DP-1 (28mm equivalent), DP-2 (45mm equivalent), and DP-3 (75mm equivalent); each of which will house a newly redesigned Foveon X3 Quattro imaging sensor as well as a radically redesigned body. Again, a Ricoh GR already exists in the same niche, but now a number of other companies have moved-in as well, most notably the Fujifilm X100S.
The Foveon X3 was remarkable for having forgone a traditional Bayer filter for a stacked imaging sensor, where each layer would absorb a different colour at full resolution—for instance a 5 megapixel sensor to capture blue light at top, a 5 megapixel sensor to capture green sandwiched in the middle, and a 5 megapixel sensor to capture red at the bottom. Sigma or Foveon would usually label such a sensor as "15 megapixels", the sum of all three imaging sensors. This is reasonable, when you consider that a traditional (Bayer filter-equipped) 15 megapixel sensor also has an average of 5 megapixels allocated to each colour (although usually biased towards green), with interpolation (guessing) filling in spaces to bring the final resolution to 15 megapixels. In practice, the Foveon sensors did not produce as sharp as a traditional sensor at the higher pixel count, and so most reviewers normalized the count for comparison, either to 1/3 the advertised resolution (the per-colour level) or some complex calculation to try and approximate the actual resolution or subjective quality.
The changes brought in the Foveon X3 Quattro sensor is as remarkable as the modernist design of the cameras. The Quattro-variant, not unlike most traditional sensors, has higher resolution in one colour than the other two. In the case of the Foveon X3 Quattro, its first layer now captures blue at 20 megapixels, but captures the other two colours at a reduced resolution of about 5 megapixels each. Each colour is still captured in successive layers, but the blue-layer can capture finer detail than the latter two which could cause false colours when viewed at the full resolution of the blue sensor, a novel problem or the Foveon X3. Nevertheless, it is refreshing to see advancements in the Foveon line, as it is a line of development quite different from traditional implementations, and in low-ISO settings has been renowned for its colour rendition.