Pi said:jrista said:Well, I think your last comparison there is a bit unrealistic. You are comparing something on the order of 100x100 pixels to a photo with millions of pixels. I don't see the same thing (that rogue aliasing) in the original photo...its crisp and sharp, but not hideously aliased like your mock example. I've seen far worse examples of real-world aliasing and moire.
Actually, the Sigma photo is not less aliased, both compared at 100%. Think of this example as a crop of a wide angle shot with a lot of people there. Also, the Sigma photo looks unnatural even downsized a lot. Anyway, which image do you prefer?
I'll see if I can find some examples of the D800 portraits I saw last year that were EXTREMELY sharp like that...and it seemed to be exactly what the photographer wanted. Sure, maybe its "aliased", but if that aliasing falls within the threshold of the photographers tolerance, I am not sure I would call it "incorrectly sampled".
I think at this point we are just debating personal preference, not any kind of real-world IQ-debilitating issue. Differing degrees of how sharp is sharp enough.
We are talking about sampling theory. Is is a personal preference whether you like aliased images or not but sampling theory is not a preference.
Just talking sampling theory, I guess I would prefer that frequencies below/around nyquist be removed or otherwise softened (most people hate the 7Ds AA filter, but personally I find it quite ideal for bird photography, it definitely avoids a lot of nasty color moire and other artifacts that are frequently caused by the overlap of birds feathers, without severely softening the results). I don't like moire in particular. I usually don't like jagged edges either, however I think whether it is "acceptable" often depends on the actual image (I do like crisp, sharp images, and the sharper they are out of the camera the less I have to boost sharpening (and therefor halos) in post).
I don't really see any jagged edges in the original photo of the girl (however that may simply be a benefit of the Retina display...will have to check on my home computer in a little bit here to see what everyone else is seeing.)
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