Dynamic range and RAW file "bit depth"

Started Jan 25, 2014 | Questions thread
GordonBGood Veteran Member • Posts: 6,306
Re: Dynamic range and RAW file "bit depth"

completelyrandomstuff wrote:

Two things, digitization is not done linearly. But more importnatly, I think the camera with 77000 electron capacity could have more dynamic range than 16.23EV, for example in case when the last few electrons filling in the well needed more light per electron than the previous ones. I would be surprised if it was a linear relationship, but I am not able to find the relationship between the photon flux and the well filling at a fixed exposure.

In fact, response is linear especially for those darker last few electrons in the darker tones as shown by extrapolating downward in the Measurement of Responsivity chart on page 9.8 of the linked paper.

There is a definition of the Dynamic Range (DR) limit as limited by quantization which is about 0.288 of the size of the LSB step so a maximum DR of about 15.79 stops for a 14 bit raw, but although one can make out details down to that level in a properly dithered processing workflow, it is mostly only interesting statistically.

In the case of the Foveon sensor, even if the full range to an electron well capacity of 77,000 electrons were used, the black read noise (not well separated from the dark current in the above link) is likely several 10's of electrons thus limiting DR to about 10 stops so there wouldn't be any point to preserving the data to a deeper bit depth as one would only be preserving mostly random noise and other undesirable effects.

Regards, GordonBGood

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