Sensors By Vincent Bockaert

The New Foveon Sensors The Current Filter Array Sensors

The cone-shaped cells inside our eyes are sensitive to , green, and —the "primary ". All other digital camera sensors only measure the brightness of each . As shown in thisdiagram, a We perceive all other colors as combinations of these primary colors. In conventional photography, "color filter array" is positioned on top of the sensor to capture the red, green, and blue components of the red, green, and blue components of expose the corresponding chemical layers of color film. light falling onto it. As a result, each pixel measures only one primary color, while the other two colors The new Foveon sensors are based on the same principle, and have three sensor layers that are "estimated" based on the surrounding via software. These approximations reduce image measure the primary colors, as shown in this diagram. Combining these color layers results in a digital sharpness, which is not the case with Foveon sensors. However, as the number o fpixels in current image, basically a mosaic of square tiles or "pixels" of uniform color which are so tiny that it appears sensors increases, the sharpness reduction becomes less visible. Also, the technology is in a more uniform and smooth. As a relatively new technology, Foveon sensors are currently only available in the mature stage and many refinements have been made to increase image quality. Sigma SD9 and SD10 digital SLRs and have drawbacks such as relatively low-light sensitivity.

Light Light

35 mm Color Film

Color Filter Array Sensor

Active Pixel Sensors (CMOS, JFET LBCAST) versus CCD Sensors Fovean Sensor Similar to an array of buckets collecting rain water, digital camera sensors consist of an array of "pixels" collecting photons, the minute energy packets of which light consists. The number of photons collected in each pixel is converted into an electrical charge by the photodiode. This charge is then converted into a voltage, amplified, and converted to a digital value via the analog to digital converter, so that the camera can process the values into the final digital image. In CCD (Charged Couple Device) sensors, the pixel measurements are processed sequentially by circuitry surrounding the sensor, while in APS (Active Pixel Sensors) the pixel measurements are processed simultaneously by circuitry within the sensor pixels and on the sensor itself. Capturing images with CCD and APS sensors is similar to image generation on CRT and LCD monitors respectively. The most common type of APS is the CMOS (Complementary Metal Oxide Semiconductor) sensor. CMOS sensors were initially used in low-end cameras but recent improvements have made them more and more popular in high-end cameras such as the Canon EOS D60 and 10D. Moreover, CMOS sensors are faster, smaller, and cheaper because they are more integrated (which makes them also more power-efficient), and are manufactured in existing computer chip plants. The earlier mentioned Foveon sensors are also based on CMOS technology. Nikon's new JFET LBCAST sensor is an APS using JFET (Junction Field Effect Transistor) instead of CMOS transistors.