Dynamic range and RAW file "bit depth"

Started Jan 25, 2014 | Questions thread
John Sheehy Forum Pro • Posts: 20,854
Re: bit depth affects PRECISION, not dynamic range so much

xpatUSA wrote:

olliess wrote:

It would make more sense to have wider spacing values as the values increase, e.g., something close to logarithmic spacing. (I believe this is what the old Compressed NEF format did with a lookup table).

Correct, see Bill Claff's article here:

I did the math a while back, and I found that a camera that has a RAW saturation of 65K electrons at base ISO needs no more than 300 levels for the top stop, 213 levels for the next stop down, 150 levels for the next stop down, etc, until you are down to where the read noise is statistically dominant and at least 1.3 ADU of your output levels, where you become linear down to the lowest original RAW values.

You really need to avoid histogram shifts in the mapping, though, as they can result in color shifts after white balance.

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