Originally posted by Eric Seavey So there is minimal processing done to the raw image data to make it possible to closely simulate the AA-filter, that would work well with lower noise images and probably some other better suited conditions.
While there is potential to somewhat address moiré at the demosaicing stage already, there is definitively no way to "
simulate" an AA-filter. As Falk wrote, the absence of an AA-filter means that some colour information will be lost forever. No subsequent processing can address this.
A moiré aware demosaicing algorithm may account for some scenarios but what if what the algorithm suppresses was actually the real scene? Without an AA-filter, the sensor is recording information it strictly speaking should not be able to record. Imagine a line of small squares with sizes so that they exactly correspond to a sensor sensel. A sensor without an AA-filter will record the same information no matter whether the squares alternate in a black and white pattern or they alternate with respective Bayer filter colours and black. If you arranged the colour squares strategically so that a red square matched a blue sensel, etc., and the colour filters in the Bayer matrix were a 100% discriminating (which they are not) then the AA-filterless sensor would record a black image, despite all the colour patches. No amount of post-processing can fully address this fundamental flaw, i.e., that you don't know what the real information was.
If an AA-filter is used, any spatial information that cannot be truthfully captured by the sensor anyhow is removed so you can fully rely on the information obtained. Due to the Bayer matrix principle, there is still a need for some level of reconstruction guesswork but, a) this is needed in both cases anyhow, and b) will produce, if any, smooth errors, not ones that are obvious at the pixel level (colour artefacts), or even image level (moiré ).
To me, removing an AA-filter is a hack. The better solution is to increase the resolution and keep an AA-filter. This achieves the same resolution advantages without the drawbacks. Of course there are challenges in increasing pixel-pitch, but I'm happy to wait for those to be addressed rather than having "fun" with artefacts from AA-filterless sensors.