FAQs: The Sigma Camera and its Foveon X3 Direct Image Sensor

 1. What image sensor is in Sigma cameras?  
 Sigma DSLR cameras contain a Foveon X3 Direct Image Sensor. A general background that highlights the unique differences between the X3 image sensor technology and the technology behind the commercial color image sensors found in other DSLRs can be found on this page that discusses Sigma’s current DSLR offering, the SD15. 

2.    The SD15 will have the following image sensor’s specifications:

3.    Who designed this image sensor?  
The image sensor was designed by Foveon, Inc. of Santa Clara, California, USA. 

 4.    Who owns Foveon? 
Foveon, Inc. is a subsidiary of Sigma Corporation. Sigma purchased Foveon and all the intellectual property involved in fabricating the X3 Direct Image Sensor and processing X3 images in November, 2008. 

 5. What does the “X3” in “X3 Direct Image Sensor” stand for?  
“X3” stands for the three-layer structure used in Sigma’s Foveon sensors. Foveon X3 Direct Image sensors use three layers of pixels embedded in silicon to capture the color that other image sensors miss. The layers are positioned to take advantage of the fact that silicon absorbs different wavelengths of light to different depths. The bottom layer records red, the middle layer records green, and the top layer records blue. Each stack of pixels directly records all of the light at each point in the image. Other image sensors have featured just one layer of pixels, capturing just one color per point the image. To capture color, the pixel sensors in CCD and CMOS image sensors are organized in a grid, or mosaic, resembling a three-color checkerboard. Each pixel is covered with a filter and records just one color—red, green, or blue. 

 6. How do you respond to people who debate the number of megapixels in Sigma cameras? 
The number of megapixels in the X3 Direct Image Sensor is simple math: Using the anticipated SD1 as an example, the sensor’s pixels are arranged in three layers throughout 15.3 million spatial (or pixel) locations. Multiply those numbers and you get 45.9, or 46 megapixels. 

The real debate stems from the definition of “pixel” versus “pixel location.” The following definitions are consistent with standard industry conventions as applied to CCD image sensors, CMOS image sensors, and the Foveon X3 direct image sensor:
A “pixel” on the image sensor of a digital camera is a light absorbing element (photodetector) that converts light (photons) into electrons. A pixel is also referred to as a pixel sensor when there is a need to distinguish the pixel from its location. 

Of course, that was prior to Foveon’s creation of an image sensor that incorporates three pixels (photodetectors) at every pixel location on the image sensor. The SD1’s 46 megapixel (4,800×3,200×3 layers) 24×16mm APS-C X3 Direct Image sensor captures all primary RGB colors at each and every pixel location, ensuring the capture of full and complete color. Using three silicon-embedded layers of photo detectors, stacked vertically to take advantage of silicon’s ability to absorb red, green and blue light at different respective depths, it efficiently reproduces color more accurately, and offers sharper resolution, pixel for pixel, than any conventional image sensor. Since color moire is not generated, the use of a low-pass filter is not required, meaning light and color, generated by the 46 megapixel APS-C X3 direct image sensor is captured with a three-dimensional feel. 

7.    The SD1 will boast new image sensor’s specifications.  They are as follows:

8.    What other features will the SD1 have? 

• Dual TRUE II image processing engine: The SD1 incorporates a dual “TRUE (Three-layer Responsive Ultimate Engine) II” image processing engine which improves the processing speed and overall quality of the final image. The unique image-processing algorithm provides high-resolution power and reproduces high-definition images with richly graduated tones.
• CF card: The SD1 adopts the TYPE I CF Card. This camera is compatible with the UDMA enabling fast processing of large amounts of data.* It is not possible to use Microdrives and TYPE II CF cards.
• 11 point twin cross sensor: The autofocus system features an 11 point twin cross sensor. The shifted twin cross type sensor improves AF accuracy.
• Magnesium body: The Sigma SD1 adopts a lightweight yet solid magnesium alloy body designed to withstand rough use and shocks in harsh conditions.
• Weather-resistant design: Buttons and connections benefit from O-ring sealing connections to prevent dust and water getting inside the camera body.
• Large, highly visible 3.0” TFT color LCD Monitor: The SD1 camera features a 3.0 inch TFT color monitor. This 460,000 pixel resolution LCD monitor benefits from a wide viewing angle, making it easy to check focusing and composition.
• Optional lenses: The SD1 can be used with over 40 Sigma lenses such as ultra-wide, ultra-telephoto, macro and fisheyes which adopt the latest technology such as the FLD (“F” Low Dispersion) glass elements, which have the performance equal to fluorite glass, SLD glass, Aspherical lenses, Sigma’s own unique Optical Stabilizer function, Hyper Sonic Motor and Sigma’s Super Multi Layer Coating. They meet the various and demanding requirements of all types of photographers.