DxOMark's measured ISOs vs. manufacturer ISOs

Started Mar 13, 2013 | Discussions thread
John Sheehy Forum Pro • Posts: 21,574
Re: Why should we trust DxO?

tkbslc wrote:

If essentially EVERY camera is 20-30% off according to DxO, then perhaps DxO are the ones that are off?

What DxO is measuring is not the metering of the camera.  If they did, there would be 3 data points for each ISO; camera-stated ISO, DxO-ISO, and camera-metered ISO.  The latter is not reported by DxOMark.

DxO's "measured ISO" is nothing more than this simple idea: the exposure index of the RAW tonal level in the green channel, some fixed number of stops below RAW saturation.  Why else do you think that "expanded" low ISOs are often the same "measured ISO" as the lowest normal base ISO?  This is a relatively unique metric which has no relationship to what we are usually talking about when we question whether or not a particular camera is mis-stating the ISO that it is metering for.

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