Advantages of Foveon sensor Locked

Started Jun 23, 2013 | Discussions thread
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bobn2 Forum Pro • Posts: 59,129
Re: Advantages of Foveon sensor

Hi Roland, thanks for re-opening - it is indeed an interesting discussion.

Roland Karlsson wrote:

In the thread named "Will Thom's prediction come true" an interesting sub-thread started - and then the entire thread did hit 150 - pang - thread closed. A rather irritation rule to say the least.

The sub-thread was about what advantages Foveon sensors have.

I said: the main advantage is that all colors are sampled in the same place and did give the reference to , where you can look at the coin above Mickey Mouse. IN particular, look at the Fuji sample, and please look at ISO 200 for the Sigma sample.

Bobn2 said: its the only advantage.

Lin and Laurence said: there are more advantages, and Laurence also listed:

  1. Edge roll-off

Not sure what that means, unless its acuity.

  1. Acuity

Well, that is an 'advantage' of missing out the AA filter, not of the Foveon sensor per se. It's also achievable by missing out the AA filter on Bayer cameras. Myself, I'd prefer to nt have the aliasing artifacts, and an AA filter, even with a Foveon sensor.

  1. no moiré

Certainly there is 'moiré' - simply not colour moiré, which is the advantage of sampling all three channels at the same point, so that is the same advantage restated.

  1. color accuracy (an arguable point for many but absolutely achievable)

Indeed it is arguable, so arguable as to be false. The Foveon sensor cannot begin to compete with a Bayer sensor for colour accuracy. The filter characteristics of the silicon depth filter is way off the optimum to match human vision and there is no simple way of correcting this.

  1. greater "presence" or a 3D effect (nebulous but mentioned in so many publications over 10 years)

Is this a real effect? As soon as people start using words like 'presence' I think we're in the area of extreme subjectivism.

Personally I would categorise all Laurence's advantages, except the one about color accuracy (4), as a result of the fact that all colors are sampled at the same position. Laurence's list is a list seen from the user perspective, which of course also is a valid way of seeing it.

NOTE that no moire (3) should be no colored moiré. Moiré overall is also less than with Bayer without AA filters, but its absolutely not "no moiré".

I would concur, and add that the 'greater colour accuracy' is absolutely false.

So - whats the advantages?

NOTE - we can all make a list of disadvantages if we want to, but can we make a list of advantages?

And - color accuracy? Is that an advantage of Foveon, as Laurence claims?

I can add three more potential advantages, which (just as Laurence's color accuracy advantage) can be discussed.

  1. The color filters in Bayer sensors, do they age?

That is a very interesting question.

  1. It is theoretically possible to add a fourth IR layer for Foveon sensors

Yes, but one big problem with Foveon sensors is efficiency loss due to two effects, one of which is the lost regions between the layers. Adding a layer makes it even worse.

  1. potentially a sensor like Foveon could detect all photons, Bayer do filter away 2/3.

That's potentially the case, but in actuality Foveon sensors lose more photons than do Bayer. Bayer filters don't in fact lose 2/3 - that is true only for the very simplistic view of how the sensors work. The Bayer design is much more subtle than that. Typically the luminance channel, 'green', which covers half the sensor area captures much more than 1/3 of the available photons in a typical scene, the luminance channels ('red' and 'blue') capture a smaller proportion, but an average scene has a smaller proportion of those photons in any case.

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