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There are different type of digital camera sensors, those sensors that can capture only one color at each photosite and those who can capture more than one color at each photosite.

Which one is better for image quality and why do most of today's camera digital sensors use the first type (the one that capture only one color at each photosite)?

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possible duplicate of What are differences between Bayer mosaic and Foveon 3 layer sensor? –  mattdm Apr 23 '12 at 20:31
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And for the why most cameras use the Bayer type: photo.stackexchange.com/questions/10742/… –  mattdm Apr 23 '12 at 20:31
    
@mattdm I read the two questions and their answers but it I'm not sure if they tell which one is better for image quality. Also they cover two types of demosaicing algorithms, I believe that there are more (Sony cameras capture four colors) but I'm not sure if they are the same –  akram Apr 23 '12 at 20:49
    
The reason the question of image quality isn't neatly answered is simply that it's still an open question. Both approaches have advantages and disadvantages. –  mattdm Apr 23 '12 at 22:58

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Capturing three colours per photosites is in principle far superior to capturing one colour and interpolation. So much so that a three colour sensor will produce an image with equivalent detail to a one colour sensor with twice as many total pixels.

Why not three times as many? Well the colour channels in an image are not independent but correlated with eachother that means knowing the red value often gives you information about the green and blue values.

Three colour sensors have the additional advantage that colour aliasing artifacts don't occur during raw conversion, meaning manufacturers can do away with anti aliasing filters to improve sharpness.

However in practice three colour sensors have problems with light sensitivity leading to poor performance in low light. In addition to this there practical/economic problems with producing three-colour sensors with high pixel densities at low cost, which is another reason why Bayer sensors despite their apparent inferiority have gained almost ubiquitous adoption.

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Isn't the anti-aliasing filter the main cause of loss of detail with Bayer sensors? (Rather than the color-per-photosite thing per se?) –  mattdm Apr 23 '12 at 22:52
    
Also, what about color accuracy for Foveon, particularly at higher ISOs? –  mattdm Apr 23 '12 at 22:57
    
@mattdm A Bayer sensor with no AA filter will still have less detail than a Foveon sensor. AA filter-less cameras often seem to have more detail due to aliasing (which with natural or organic textures looks like detail). Think about a 12MP Bayer sensor shooting a scene with only red objects, the blue and green pixels receive no light so you really only have a 3MP image. A 12MP Foveon (36MP in Sigmas marketing speak) would get 12 million red samples and give a true 12MP level of detail. –  Matt Grum Apr 23 '12 at 23:16
    
But in practical photography, as you point out, there's usually correlated information. Between that and the lack of an AA filter, doesn't that make a pretty close horserace? –  mattdm Apr 23 '12 at 23:23
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@mattdm a little closer, yes, but part of the perceived sharpness gain from removing the AA filter is actually aliasing, and then there's the disadvantage of colour moire in fabrics. What you actually want is to cram so many megapixels in the sensor that you can do away with the AA filter, and bin different coloured pixels together if necessary to get Foveon style dense colour sampling, but without the low light penalty or huge cost. With 24MP crop sensors arriving that day is close! –  Matt Grum Apr 24 '12 at 13:42

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