[Brightcolours]

Well, there's a bit of debate about the effective resolution from a bayer sensor. 

It also depends on the specific sensor. Most work with 4x4 layouts, but Fuji has 6x6.

 

Honestly I don't dare to make a statement myself but I have seen figures around the 67-75% mark of the nominal value (ok, thus 26-29mp to match the 19mp Foveon).

 

29mp is also the figure from Sigma for their interpolated images (only god knows why they do that because the RAWs are 19.6mp on the APS-C model).

Bayer only loses you a few percentages, actually (around 10-12% if I remember correctly). It does matter which kind of demosaicing is used, that is why some RAW converters give more detailed images than others.

And Sigma just counting very pixel 3 times with the older foveon and now a bit less with the quattro nonsense is just childlike silly, to be honest. It really does have 19mp.

 

The reason Sigma foveon looks so sharp is mostly down to no AA-filter (which then just just mostly fake extra sharpness). And yes, with saturated to dark primary colours, they have a resolution advantage with blue. Not anymore with green or red.

 

They capture blue detail for every pixel. They capture less green detail (half of it) compared to a bayer CFA. They capture the same red detail as bayer CFA