If I understand correctly, sensors can produce a moire effect because their subpixels are separate (each one is affected by a different portion of the image), so to stop this effect, some cameras have a blur filter in front of the sensor, but this reduces the image quality by a lot.

My question is, why don't camera makers add a blur filter for each individual pixel, so that all subpixels receive the same amount of light, but none of the blurred light reaches another pixel (this could be done either by making the filter bubble around each pixel, or by adding a frame, preferably a reflective one, to separate the pixels before blurring)? Is it only because it would increase the cost for producing them?

Sorry if there's something I'm not understanding, I'm a programmer and don't have a lot of experience with cameras.

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Moire occurs because the scene is sampled at a discrete resolution which is the nature of digital imaging. There is nothing to do about that but reduce the frequency of the signal reaching the sensor.

In fact, moire occurs in monochrome sensors too which have no sub-pixels. The matrix of pixels form a fixed grid to sample an image formed by incoming light and anytime that image has a higher frequency than the sampling from the sensor, it risks causing aliasing which appears as moire for high-frequency patterns.

You may have noticed that many cameras no longer feature anti-alias filters which allows the possibility of moire but it still occurs very rarely. Most times, one only need to stop down the lens or change the focal-length and moire disappears. There is a demo on my site where you can play with the aperture and see what happens to an image specifically selected to cause moire with two cameras which only differ in the fact that one of them has an anti-alias filter and the other does not. You will notices that moire occurs on both cameras and that with apertures beyond the diffraction limit, neither shows any.

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