Advantages of Foveon sensor Locked

Started Jun 23, 2013 | Discussions thread
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Kendall Helmstetter Gelner
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You are more wrong than right.
In reply to bobn2, Jun 24, 2013

Bobn2 wrote:

Kendall Helmstetter Gelner wrote:

Bobn2 wrote:

<...>

That's potentially the case, but in actuality Foveon sensors lose more photons than do Bayer.

In actuality they lose almost none, can you truly disagree that most of the photons hitting the sensor end up in the sensor at one depth or another?. It's the processing that matters.

Sorry, you are incorrect. The quantum efficiency of Foveon sensors is low, meaning that they lose a lot of photons - as in fail to count them. There are two reasons for this. One is that there are dead bands between the layers, where the collected photoelectrons fail to make it to the gate of any read transistor. If those bands were not dead the colour selectivity would be even worse than it is. Secondly tehre is incomplete charge transfer from the lower layers. Incomplete charge transfer means, simply that photons don't get counted and the quantum efficiency is poort. poor QE is why Foveon sensor don't do so well at high ISO's - if they were truly capturing more of the photons than do Bayer sensors they would be better in low light - but they are not.

Yes, it is the case some is lost.  But that was never the main issue.

That 'simple and obvious absolute' is wrong, and derive from a misunderstanding of the principles of colour vision, the nature of filters and the how colour photography works. Indeed, there is no definition that says a Bayer filter blocks 2/3 of all photons ever reaching the sensor. Consider the following:

- The number of photons blocked in any case depends on the wavelength distribution of the light reaching the sensor. That distribution depends both on the colour temperature of the light source and the colour reflectivity of the subject.

It doesn't matter what the incoming spectrum is like.  At best in an ENTIRELY green image, you only discard half of all photons coming your way - because ALL data hitting red/blue filters is lost.  On average, in 99.999999999999999999% of every image that ever has or will be shot, you are in fact tossing away 2/3 of all photons hitting the filter.

The ORIGINAL MESSAGE I responded too simply claimed that you didn't lose 2/3 of the photons hitting the SENSOR.  You have to totally ignore what a PHYSICAL FILTER does to photons of different wavelengths that hit it.

It is madness to start talking about luminance and human color vision when the only question here is - how many photons will make it past a PHYSICAL FILTER to reach the sensor.

Sorry for the all caps, but it appears you and a few other people at least are just blowing right past the real question.

- Filter passbands can and do overlap.

By very little in Bayer system (generally).

Now can you see that your 'simple and obvious absolute' is not at all absolute.

You just ignored the question and went to prove a point that no-one was asking about.  In reality a physical filter does in fact filter the same way. Every. Single. Time.

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