Is capture sharpening still necessary with images made
by cameras with no AA filter?
Hi Dale,
Yes, because the lens has residual aberrations, and it adds diffraction blur, and the sampling aperture of the sensor's photosites averages the details over an area (thus lumping all additional detail, or diffused detail from the lens blur, into one average value per pixel). Most good lenses+sensors produce something like a Gaussian kind of blur with a radius of 0.7 at their optimal aperture, more for other apertures.
All that a sensor without Optical Low Pass Filter (OLPF, or AA-filter) does, is boost the MTF (the contrast at various spatial frequencies) and add aliasing artifacts. It does very little to increase resolution, except for the finest low-contrast detail near the resolution/sampling limit (Nyquist frequency) of the sensor. The (lens+sensor aperture) blur is is still recorded.
The aliasing does make it more difficult to apply proper deconvolution Capture sharpening, without exaggerating stair-stepping of sharp lines and edges and other manifestations of aliasing (like e.g. False Color moiré).
Cheers,
Bart
