What the imager has

Started 10 months ago | Discussions thread
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Re: Once more with feeling
In reply to DickLyon, 10 months ago

DickLyon wrote:

But the "stronger" and "weaker" is not quite right. The high-frequency blue photons are stronger (highest energy); but the way they interact with silicon makes them get absorbed soonest, near the surface. The lowest energy photons, in the infrared, penetrate deep. Low frequencies, at wavelengths greater than 1100 nm, where the photons are quite weak, are not able to kick electrons out of the silicon lattice at all, so the silicon is completely transparent to them. In between, there's a nicely graded rate of absorption.

Understanding the spectral responses of the layers starts with understanding that at any wavelength, the light intensity decreases exponentially with depth in the silicon. I think I've written about this some place... Anyway, the top layer is not white, not luminance, not blue, but a sort of panchromatic blueish that turns out to work well enough for getting a high-frequency luminance signal. We did a lot of experiments and amazed ourselves how "well enough" the 1:1:4 worked; it was not obviously going to be a good thing, but turned out awesome.

We had 1:1:4 sensors working, including very efficient and effective hardware and software processing pipelines, before I left Foveon back in '06, but the sensors didn't yet have the low-noise fully-depleted top-layer photodiodes of the "Merrill" cameras, and we were only targeting these for cell phones at the time. I expect it will be a killer combination: fully-depleted blue plus 1:1:4. I don't think the red and green are fully depleted, too; that was thought to be somewhere between hard and impossible, which is why they don't have the same low read noise, and one reason why aggregating red and green quads this way is a big win.

But understanding how it compares to the classic Foveon and to Bayer will keep many people busy for a long time. Something for dpreviewers to do while waiting for cameras, and something to keep the marketing people tied up... Should be fun.



So potentially the 4.9 mp middle and lower layer could produce a cleaner (better color accuracy and more detail, less noise) result then the Merrill sensor's middle and lower layer.  Which would make the new sensor quite a bit superior in overall quality to the Merrill sensor in most situations?

Also with the assumption that the middle layer collects cleaner results then the bottom layer, when Sigma/Foveon make a bigger sensor would a 1:4:16 (bottom:middle:top layer) make sense to produce even superior results when the sensor gets big enough to support that resolution?

Thank You for any insight you can give

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