AA filter question - Joe?

Started Feb 9, 2012 | Discussions thread
John Sheehy Forum Pro • Posts: 20,088
Re: The two sides of "insane resolution"

DSPographer wrote:

This would be right for a monochrome sensor. But, for a color Bayer array sensor we use the spacing of the green pixels for the unambiguous luminance sampling. We then need to consider that the lines could be at a 45 degree angle: then the green pixels are 1.414 times as far apart as the base pixel spacing. The result is you need to double your pixel counts for a color sensor.

With a 2x2 pixel CFA pattern, you may also want to get a red-filtered or blue-filtered grayscale or B&W image. For blue, with its very weak diffraction, aliasing can be quite a problem, even at very high pixel densities.

Look at this crop of the RAW blue channel from my Casio EX-FH25, with 1.5 micron pixels (3.0 micron spacing for blue), of classical guitar strings with specular light on them:

Now, you can say that DSLR lenses are not as absolutely sharp as small format lenses, but I think at f/7.9 we should be into the diffraction-limited range, and there are DSLR lenses that are supposed to be diffraction-limited at lower f-numbers. This is from a bulb with multiple blue wavelengths; a narrow-band blue LED would probably be even sharper.

If we consider all possible uses of a camera, we are far, far from non-aliased, unfiltered imaging with today's highest pixel densities.

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