Editing Foveon X3 sensor (section)

===Spatial resolution===
According to [[Sigma Corporation]], "there has been some controversy in how to specify the number of [[pixel]]s in Foveon sensors."<ref>{{cite web|url=http://www.cameratown.com/news/news.cfm/hurl/id%7C3599|title=Sigma SD14 White Papers|access-date=2007-04-29|archive-date=November 26, 2007|archive-url=https://web.archive.org/web/20071126090538/http://www.cameratown.com/news/news.cfm/hurl/id%7C3599|url-status=dead}}</ref> The argument has been over whether sellers should count the number of photosites or the total number of photodiodes, as a megapixel count, and whether either of those should be compared with the number of photodiodes in a [[Bayer filter]] sensor or camera as a measure of resolution.

For example, the dimensions of the photosite array in the sensor in the Sigma SD10 camera are 2268 × 1512, and the camera produces a native file size of those dimensions (times three color layers), which amounts to approximately 3.4 million three-color pixels. However, it has been advertised as a 10.2 MP camera by taking into account that each photosite contains stacked red, green, and blue color-sensing photodiodes, or [[active pixel sensor|pixel sensors]] (2268 × 1512 × 3). By comparison, the dimensions of the photosite array in the 10.2 MP Bayer sensor in the Nikon D200 camera are 3872 × 2592, but there is only one photodiode, or one-pixel sensor, at each site. The cameras have equal numbers of photodiodes and produce similar raw data file sizes, but the [[Bayer filter]] camera produces a larger native file size via [[demosaicing]].

The actual resolution produced by the Bayer sensor is more complicated than the count of its photosites, or its native file size might suggest; the demosaicing and the separate anti-aliasing filter are both commonly used to reduce the occurrence or severity of color [[moiré pattern]]s that the mosaic characteristic of the Bayer sensor produces. The effect of this filter blurs the image output of the sensor which produces a lower resolution than the photosite count would seem to imply. This filter is mostly unnecessary with the Foveon X3 sensor and is not used<!-- In general or for a specific camera? -->. The earliest camera with a Foveon X3 sensor, the [[Sigma SD9]], showed visible luminance moiré patterns without color moiré.<ref>
{{cite web|url=http://www.dpreview.com/reviews/SigmaSD9/page23.asp|title=Sigma SD9 Review|work=DPReview|author=Phil Askey|date=November 2002}}
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Subsequent X3-equipped cameras have less aliasing because they include micro-lenses, which provide an [[Anti-aliasing filter#Optical anti-aliasing filter|anti-aliasing filter]] by averaging the optical signal over an area commensurate with the sample density. This is not possible in any color channel of a Bayer-type sensor. Aliasing from the Foveon X3 sensor is "far less bothersome because it's monochrome," said Norman Koren.<ref>
{{cite web|url=http://www.imatest.com/docs/print_sharpness.html|title=Sharpness: What is it and how is it measured?|work=Imatest docs|author=Norman Koren|access-date=2007-12-16}}
</ref> In theory, it is possible for a Foveon X3 sensor with the same number of photodiodes as a Bayer sensor and no separate anti-aliasing filter to attain a higher spatial resolution than that Bayer sensor. Independent tests indicate that the "10.2 MP" array of the Foveon X3 sensor (in the Sigma SD10) has a resolution similar to a 5 MP<ref>
''Popular Photography & Imaging'', Vol. 69, No. 6 (June, 2005), (table on p. 47).
</ref> or 6 MP<ref>
[http://www.dpreview.com/reviews/sigmasd10/page17.asp Digital Photography Review: Sigma SD10 Review], March 2004, Retrieved March 3, 2007.
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Bayer sensor. At low [[film speed|ISO speed]], it is even similar to a 7.2 MP<ref>
c|net Reviews, [http://reviews.cnet.com/Sigma_SD10/4505-6501_7-30588638.html Sigma SD10] Retrieved March 6, 2007.
</ref> Bayer sensor.

With the introduction of the [[Sigma SD14]], the 14 MP (4.7 MP red + 4.7 MP green + 4.7 MP blue) Foveon X3 sensor resolution is compared favorably by reviewers to that of 10 MP Bayer sensors. For example, Mike Chaney of ddisoftware says "the SD14 produces better photos than a typical 10 MP DSLR because it is able to carry sharp detail all the way to the 'falloff' point at 1700 LPI, whereas contrast, color detail, and sharpness begin to degrade long before the 1700 LPI limit on a Bayer based 10 MP DSLR."<ref>
{{cite web | url = http://www.ddisoftware.com/sd14-5d/ | title = Sigma SD14 Resolution: 14 MP? 4.6 MP? How does the SD14 stack up against high-end cameras like the Canon EOD 5D? | author = Mike Chaney | work=ddisoftware | year = 2007}}
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Another article judges the Foveon X3 sensor as roughly equivalent to a 9 MP Bayer sensor.<ref>{{cite web|url=http://www.popphoto.com/howto/4276/foveon-x3-sensor-claims-put-to-the-test-color-resolution-vs-b-w-resolution-page2.html |title=Foveon X3 Sensor Claims Put to the Test |url-status=dead |archive-url=https://web.archive.org/web/20080205032245/http://www.popphoto.com/howto/4276/foveon-x3-sensor-claims-put-to-the-test-color-resolution-vs-b-w-resolution-page2.html |archive-date=February 5, 2008 }}
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A visual comparison between a 14 MP Foveon sensor and a 12.3 MP Bayer sensor shows Foveon has crisper details.<ref>
{{cite web|author=Carl Rytterfalk|date=February 23, 2010|url=http://www.rytterfalk.com/2010/02/23/a-tiny-sigma-sd14-vs-nikon-d90-comparison/|title=A tiny Sigma SD14 vs Nikon D90 comparison..|website=Carl Rytterfalk Photography|url-status=dead|archive-url=https://web.archive.org/web/20100715011940/http://www.rytterfalk.com/2010/02/23/a-tiny-sigma-sd14-vs-Nikon-d90-comparison/|archive-date=2010-07-15|access-date=May 20, 2010}}
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