Advantages of Foveon sensor Locked

Started Jun 23, 2013 | Discussions thread
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Lin Evans
Lin Evans Forum Pro • Posts: 17,390
Re: Advantages of Foveon sensor

John Sheehy wrote:

Lin Evans wrote:

It' is "very" precise Bob, but because you don't know and understand the term, your knowledge of how to relate to it is faulty.

Normally, I wouldn't bother to repeat what is quite commonly known here on the Sigma forum, but for your elucidation: Edge roll-off is a very simple concept. How many pixels are there which separate adjacent detail objects? If you photograph a very plain and featureless pure black object with sharp edges on a pure white and featureless backdrop, at the edge boundaries there is not a single pixel of black adjacent to a single pixel of white. There are a number of pixels, from the black perspective of varying shades of gray until finally a pixel of 255, 255, 255 white. If you make the identical photograph with a CFA based camera using identical focal length, identical pixel file dimensions, identical ISO, identical lens and other relevant settings, there will be fewer pixels separating the white and black with the Foveon sensor. This is irrespective of the AA filter which adds to the number of these pixels. The CFA process itself creates additional transiting pixels. The Foveon image is therefore sharper than the CFA image. It's been tested, measured and posted on this forum and discussed numerous times.

Really John,

A camera "should not" be able to record a black pixel next to a white one??? If it could, it would represent "reality" much better than our best cameras do. In reality there are no "pixels" separating black from white. There is, under microscopic examination, black and then there is white. They lie "immediately" adjacent to one another.

A camera which better "approximates" this produces a "sharper" image. The more transiting pixels at edge boundaries the softer the image. There are myriad so called "sharpening" techniques which attempt to fool our eyes and brains into thinking that fewer of these pixels exist - that's what edge contrast enhancement is all about.

You are stereotyping "Sigma Fans." This Sigma fan is interested in "performance" and image quality. Where my Sigma cameras do it best I use them; where my CFA cameras do it best I use them. It's really quite simple actually.


A camera should not be able to record a black pixel next to a white one. If it can do it, it will also fail to do it by translating the edge 1/2 pixel. If your edge changes 1/2 pixel vertically, every 100 pixels, what you wind up with a hyphenated series of alternating gray lines, and black&white transitions. As is typical of most Sigma fans, you are more interested in a sense of sharpness that occurs somewhere in the image, but not necessarily consistently, than in any consistent real sharpness from the analog lens projection. Sigma/Foveon and Bayer cameras both are terrible at pixel-level detail, but in different ways. The real solution, of course, is much higher pixel densities.

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