Am I oversharpening

In message <>,

Not at all; unlike the 13.7MP output from the Sigma software, 6MP Rebels
actually take a measurement at 6M locations on the sensor. The 13.7MP
Sigma images are merely aliased 3.43MP images softened in upsampling;
the stair-steps get a plush carpet.
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They do not because they do not have RGB sensors. They have three
stacked sensors that are mostly monochrome with a slight bias to red,
green, or blue. It takes significant processing to coax out color
information.

 

In message <>,

Download "IRIS", load some .x3f files, and then maybe you might have an
idea.
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In message <>,

Why not?

Actually. there is no loss of color coverage at all; the AA filter makes
sure that a high percentage of light of all colors hitting anywhere on a
particular point of the sensor plane reaches the three color sensors.
It is just not possible to record color details above a certain
frequency, which is a bit lower than the frequency of luminance detail
recorded. We generally can't see color detail at those frequencies
anyway, with normal viewing situations.

Foveon does not give all. Foveon gives partial. Foveon has three color
channels, but they are not particularly distinct, and the hue resolution
can be pretty coarse, especially in the blue/green range. And the
blue/green seems to often vary in large, obvious blotches, rather than
in a manageable fine dither.

Also, none of the current x3f-based cameras have proper aliasing, so
they do not give you full spatial information. On the SD9, the capture
has a very strong "snap-to-grid" effect, at the pixel level, and this
makes the images look artificial to me. There are lots of artifacts
that alighn themselves in horizontal and vertical lines, something that
does not happen in real vision.

If the Sigma cameras had proper AA filters, they would be better, IMO,
but a lot of the people drawn to them might not like them, because they
like the artificial sharpness of aliasing.

You can reproduce the effect easily with any Bayer camera; upsample with
bicubic to twice the dimensions of a Sigma image (4536*3024), and then
downsize to 2268*1512 with Nearest Neighbor. Voila! Instant SD9 "pop"
and staircase effects.
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