What the imager has

Started Feb 11, 2014 | Discussions thread
DickLyon New Member • Posts: 7
Re: What the imager has

Truman Prevatt wrote:

DickLyon wrote:

So, it's complicated. Yes, reduced chroma resolution is a compromise; but a very good one, well matched to human perception -- not at all like the aliasing-versus-resolution compromise that the mosaic-with-AA-filter approach has to face.


disclaimer: I've been away from this technology too long to have any inside knowledge. And give my apologies to Laurence for my too many words.

At the end of the day the reason we test weapons is so we will know how they really work when it counts instead of how the work in computer models. The same is true with image sensors which have to make trades where sub- alias sampling is going one be it Bayer or the new Sigma design. There will be artifacts from aliasing from the lower level detectors. The question is how will it show up and under what conditions will it be noticeable? Hopefully we will find out soon.

It will most likely be that it will solve more problems than it creates but with all trade offs there will be downsides.

Truman, I guess you missed the bit where I wrote "A lot of people seem to have the idea that aliasing has something to do with different sampling positions or density, as in Bayer. But that's not the key issue. ..." It must have been your comments that prompted that. What is "sub-alias sampling" supposed to mean?

Sure, there will be aliasing, as in all sampled images. If you consider the pixel pitch and pixel aperture, you can work out that the aliasing will be about like that of the SD15's sensor. That is, negligible; and that will only be in chroma, so even more negligible, visually. The key next step is adding a high-frequency luminance signal, uncorrupted by that aliasing. That's what's nearly impossible to get accurately in Bayer sensors, but trivial to get with the Foveon 1:1:4.

But you are certainly right, as I also said, that we will wait and see. My words and yours are not going to convince anybody of anything until they see it.

As I also said elsewhere, I'm both surprised and delighted, after 8 years away from Foveon, to see this concept making it into a Sigma camera. It shows that Kazuto had the courage to focus on image quality above all, not fearing the marketing difficulty of explaining the Foveon advantage a little differently and with lower pixel numbers than before. As Laurence said, Merrill worked on this idea from its inception; Foveon's cell-phone sensor project did enough testing to show it's a great idea. And I presume the rest of the Foveon team has continued to execute well on the potential in bringing it to the larger format.  This may be Merrill's best legacy, even more than the ones named for him.

If I may summarize once more what I think is the key point: the tradeoffs and compromises about how to utilize the Foveon concept and technology have been thought through here, and developed and tested for many years, in a way designed to maximize image quality at both low and high ISO. The 1:1:4 architecture is surprising and non-intuitive, but it is what best exploits what the silicon can do (as Carver said, years before we started Foveon, "listen to the silicon" http://www.wired.com/wired/archive/2.03/mead.html).  Listening is not a theoretical exercise, nor something you do in computer models (though they help).


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