Luminance aliasing in practice (Comparison using Bayer shots)

Started Apr 21, 2012 | Discussions thread
Gary Dean Mercer Clark
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Re: I see your point...
In reply to DMillier, Apr 22, 2012

I see those jaggies in foveon image that are saved to .jpeg so I assumed these were .jpeg artifacts. What I've always done if I know an image is being saved to .jpeg is that I sharpen the image til I see the jaggies at 100 percent then I step back the sharpening so they just disappear. I understand what you are talking about but in practical terms, this is a very tiny problem. I thought the lack of an AA filter helps the foveon images. What about using one of those anti aliasing filters that you put on the front of the camera? You could get one for about $130 dollars and test your theory---just screw it on to the front of the lens and see if the jaggies go away?

DMillier wrote:

Hi

What happens in prints is not that you observe the jaggies directly (although you can actually with blades of grass in the foreground) but that you perceive a roughness to areas such as complex criss-crossing twigs and branches. It's a similar roughness that you get with a noisy over-sharpened image. The edges of things start to look rough and crude rather than smooth and natural. You never see this effect with film and it screams "digital" to me.

One of the best things (for me) about Foveon is not the sharpness and detail people like to go on about, but the easy, unforced, "naturally sharp" look you get in the best images. There's little of the aggressive, forced sharp look you get when people over process for impact. However, this is spoilt when aliasing is present - it looks rough, unnatural and digital again.

I thought the screenshot helps to explain why: the aliased edges look wrong close up but from a distance they behave a bit like sharpening, enhancing the edge sharpness. But where you get interacting aliased sections such as between the concentric circles, you get a combined sawtooth effect. If you have a mass of this kind of stuff (such as dense foliage winter with no leaves) it looks like a horrible mess.

You can see this even with the amazing D800e resolution. Take a look at Reichmann's proud "no moire" shot. If you look very carefully for the same kind of effects you see in the coin edges, you can find some nasty, ugly stuff in this picture:

http://www.luminous-landscape.com/1photo-pages/day_for_night.shtml

Twigs and fine detail that looks made from lego....

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Gary Mercer

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