DxOMark's measured ISOs vs. manufacturer ISOs

Started Mar 13, 2013 | Discussions thread
Martin.au
Martin.au Forum Pro • Posts: 13,293
Re: DxOMark's measured ISOs vs. manufacturer ISOs

John Sheehy wrote:

Mjankor wrote:

Perhaps you could describe an experiment that would help me understand what it is you're trying to show. I have two cameras here, one of which has DXO ISO of 211, at ISO 200, and the other of which has DXOISO of 107 at ISO 200. What can I do, or what results should I expect, with those cameras?

That means one thing, and one thing only: The DxO-ISO 107 camera has log(200/107)/log(2) = 0.9 stops more headroom, in terms of absolute exposure. IOW, if you meter a scene for "sunny f/16" or meter with an external ambient light meter, the clipping level will be 0.9 stops higher for the DxO-ISO 107 camera.

It tells you nothing directly about noise levels, image brightness with default conversion, or clipping relative to the camera's metering, or what ISO exposure index the camera is metering for.

It's only about how many photons fall on the sensor per unit of sensor area when the RAW data clips in the green channel (except maybe with rare sensors that clip the red or blue channels first, in which case I don't know what they do).

DxO-ISO has nothing, whatsoever, to do with the issue of manufacturers fudging their ISO sensitivities, in their metering and default conversions. They are two completely different things, that simply have "ISO" in their names.

You make sense and what you write correlates with my reading on the subject thus far.

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