Hi Graeme,
This is where sampling theory and photographic reality collide. When I look at a b&w resolution chart at Nyquist a CFA sensor produces mush. When I shoot a landscape with grass, pine needles, leaves, etc., and enlarge a CFA print I get to a point where "mush" is very apparent. When nine converging lines on a resolution chart can no longer be resolved the AA filter produces a blob of indistinguishable grey plus color moire. In real-world photography this point is evident throughout when I reach the visible limits of resolution. These artifacts are far more objectionable to me than what you describe.
When my SD10 or SD14 stop resolving nine converging lines, I see five lines. Is this "real"? No - it's false detail but I still see "lines" not mush. Whether I see five blades of grass in my enlargement where there should be nine, or five pine needles where there should be nine on distant trees is largely unimportant as long as I still see something which resembles grass or pine needles or fur on wildlife (whose counting?). In my enlargements this false detail looks much more realistic than having an indistinguishable blob at the point of resolution exhaustion.
Would I like more "resolution?" Sure. But no matter how much "resolution" I have, an antialiasing filter simply at some point in the equation produces moire and blur which I don't want in my enlargements.
In the real world this lets me make larger prints and tighter crops from my Foveon based Sigma than with even my 12 megapixel CFA sensor and "still" hold the interest of my audience. The reality is that with AA filtering not having visible stairstep aliasing eventually causes color moire and resolution extinction blur and having more resolution only pushes the point at which it appears further along the enlargement scale, it doesn't prevent it. All that it does is soften the edges and smooth out stairsteps. For some that may be a wonderful thing, but my walls are full of huge prints which show no visible aliasing and that's what I want an what my customers want.
Why do you think AA filters are rarely used on MF backs??? Why did Kodak not use one on their 14 series and why did they have a removable AA filter on earlier DCS pro-line cameras?? It's because for many jobs it produces a superior product - not "nasty aliasing". Yes indeed whether or not one "likes" the look of the image (not likes or dislikes aliasing) is the true issue. One doesn't look at the printed image from an inch away and never see a single pixel - that's what interpolation is all about. The issue of "aliasing" with the Sigma/Foveon sensor is a very minor one and the improvements in sharpness, enlargeability and realistic appearance of prints more than compensates the small amount of controllable stairstep aliasing. Unless you are pixel peeping with zoom it's rare to even see this type aliasing in prints.
In short, complaining about a Sigma SD14's "aliasing" is a solution in search of a problem.
Best regards,
Lin
If you like the look of aliasing artifacts or not, that's subjective. That they exist, and can be measured is not subjective but objective. Quite frankly, if you had a detailed enough resolution chart, you'd still be measuring resolution way beyond the pixels on your sensor if you don't stop when aliasing starts to occur. It's a joke to suggest that heavily aliased data is real resolution when it's an undesirable artifact. If you could keep your resolution as-is, but not have any aliasing, would that not be beneficial to your images?
Graeme
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