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This question already has an answer here:

What are the advantages and disadvantages of Foveon X3 sensor compared to sensors that use Bayer filters or other color filter arrays?

Using resolution, noise, and light gathering performance.

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Also see What happened to Foveon sensors? –  mattdm Apr 27 '13 at 12:04
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marked as duplicate by Dan Wolfgang, mattdm, Paul Cezanne, Michael Clark, John Cavan Apr 27 '13 at 16:25

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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The X3 sensor records three colour values per photosite instead of one. This reduces ambiguity in rendering fine detail compared to Bayer or other one-colour-per-photosite sensors, reducing the need for an anti aliasing filter (which blurs the image so that light falls across more than one photosite). This results in great per pixel sharpness and very natural rendering of fine colour details and lack of colour moire, which is the advantage of the X3.

Unfortunately there are many disadvantages:

  • Resolution is on average slightly lower than Bayer sensors with the same total number of detectors. Why is this? Well imagine you have a 15MP X3 sensor and a 45MP Bayer sensor. Now if you're photographing a gig and there is only a red light pointing at the stage, then the green and blue photosites of both sensors will not record any signal as there is no green or blue light coming into the camera. So you'll get a 15MP image from the X3 as you'd expect, but the Bayer image will be interpolated from only 11.25 red pixels. Advantage Foveon. Now reverse the situation and imagine shooting an image of a grey cat against a white background. Now the incoming quantities of red, green and blue light are equal everywhere in the image. The X3 sensor produces a 15MP image as before, as there are only 15 million difference positions light is recorded across the image plane. The Bay sensor produces a true 45MP image as it records light from 45 million different positions across the image plane, and loses no information. These are extreme cases, but in practice it works out that a Foveon sensor is equivalent to a Bayer sensor with twice the number of pixel locations, i.e. a 15MP (45MP if you read Sigmas marketing) X3 ~= 30MP Bayer.

  • Limited adoption means fewer tools to process RAW images. Simga's own RAW converter has been widely criticised for ease of use issues. Also people may already have their own workflow for Bayer images.

  • The X3 is currently only available in APS-C size or smaller, 15MP max resolution so far. Bayer sensors have been commercially in medium format and larger with over 100 megapixels.

  • Development is not keeping pace with Bayer sensors which are growing larger all the time. Eventually Bayer sensors will be high enough resolution to use oversampling to get round the one colour per pixel problem, meaning eventually Bayer technology will win out due to it's simplicity (in my opinion).

  • Sensitivity is not as good, blue light has to penetrate both the red and green pixels to register. This results in very noisy images in anything other than very good light.

  • Colour reproduction is poor for certain colours for the same reasons.

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Maybe merge this into your older answer on the earlier question? –  mattdm Apr 27 '13 at 16:56
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