If you make a Bayer sensor without a blurring filter, will it be as sharp as a Foveon?
No. Even if the optical image is perfect, Bayer interpolation will blur it. This interpolation is based on averaging, so whenever black is next to white, grey will be interpolated between them. That is why it is important not to enlarge Foveon images using an interpolating algorithm that takes a running average. Enlarging Foveon images by taking a running average will create blur.
