The Foveon X3 Image Sensor World's first full-color image sensor puts pixels in a different light Until now, anyone shopping for a digital camera could rely on using the number of pixels as a metric for determining image quality. It has been reliable to assume that digital cameras with higher numbers of pixels will produce better images than digital cameras with fewer pixels (given equal optical quality with both systems). With the debut of Foveon X3 technology in the Sigma SD9, it's apparent that all pixels are not created equal. To understand this difference, it helps to understand what pixels are and why they are important. So what exactly is a pixel? In an image file such as a TIFF or JPEG, each pixel in the file is defined by a location and a color. The pixel's color is typically represented by values of the primary colors red, green and blue. These values indicate the amount of each primary color required to produce the specific color. It has been reasonable to assume, therefore, that the image sensors (both CCD and CMOS) used in digital cameras capture all three primary colors for every pixel location. Many will be surprised to learn, however, that this is not true. Current conventional image sensors in fact capture only one color per location. The result is that current filtered mosaic-type digital cameras are delivering image quality that is not near the potential of what is possible if three colors per pixel were captured. Silicon Valley-based Foveon Inc. has introduced a technology that delivers on this potential and is changing the rules we use to understand image quality. The significance of Foveon's new technology can be best appreciated when compared to conventional image sensors. Today's digital cameras capture light using an image sensor that comprises a single layer of photodetectors which are organized as a grid. Photodetectors are the physical silicon elements that record the light that hits the sensor. The problem is that photodetectors do not discern color. To capture color, the grid of photo-detectors is covered with color filters in a pattern resembling a three-color checkerboard such that each photo-detector detects the color for only one of the three primary colors. Since three colors are required for each pixel location in an image file, the missing colors have to be estimated through complex processing and interpolation. This estimation process typically reduces the sharpness of the resulting image. To provide products with increased sharpness, digital camera companies bring out cameras that have more pixel locations. The Foveon X3 image sensor uses a new method for detecting color that maximizes the sharpness for the same number of given pixel locations. Instead of capturing one primary color per location, Foveon X3 technology captures all three primary colors. This is accomplished by stacking three layers of photodetectors at each pixel location. The layers are positioned to take advantage of the well-established fact that silicon absorbs different colors of light at different depths; one layer of photo-detectors records red, another layer records green and the third layer records blue—much the way conventional three-layer color films work. It is for this reason the company claims that their X3 image sensors are the world's first full-color image sensors. The Sigma SD9 is the first camera to use the new Foveon X3 technology. The camera uses the 3.43-million pixel Foveon X3 Pro 10M image sensor. Since each pixel location has a stack of three photodetectors, there are over 10.2 million photodetectors on the X3 sensor. In contrast, a comparable single-layer image sensor with 3.43-million pixel locations would have 3.43 million photodetectors. Additionally, information from all pixels is retrieved simultaneously with the Foveon X3 sensor, rather than row-by-row as with conventional sensors. By utilizing three times the number of photodetectors over single-layer image sensors, the Foveon X3 technology captures a higher density of information which produces more sharpness for the same number of pixels. With the introduction of Foveon X3 technology, counting the number of photodetectors becomes more relevant than counting pixels when comparing digital cameras.