Advantages of Foveon sensor Locked

Started Jun 23, 2013 | Discussions thread
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bobn2 Forum Pro • Posts: 56,089
Re: There is at least one absolute, and you refuse it.

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.

Bayer filters don't in fact lose 2/3

In discussions in photography there are a lot of things that are more subjective than not, because there are so many moving parts - things like color accuracy for example, when people could use any number of options for processing RAW, all of which have their own take on what color means. All of that fed into monitors that may more may not be calibrated, may or may not be calibrated well. Then viewed by eyes that may will interpret color slightly differently one person to the next...

However in this world of subjective reflected dream capturing that we all take part in, there is at least one physical absolute that remains true now and forever. By definition, a bayer filter does in fact block 2/3 of all photons from ever reaching the sensor. That's just how filters work. When talking about photons it does not matter that humans happen to "see" luminance more clearly, it's a matter of the most basic physics, a colored filter letting through some wavelengths and not others.

If you can't admit that simple and obvious absolute, what are we to make of the rest of your positions?

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.

- Filter passbands can and do overlap.

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

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