D4 vs 1Dx (Imaging Resource), RAW, ACR, 6400-12800

Started Sep 4, 2012 | Discussions thread
Jack Hogan Veteran Member • Posts: 6,686
What is ISO?

bobn2 wrote:

It's not a 'cheat' - it's DxO getting confused about what ISO is.

I hear you, but aside from terminology I typically find DxO's science pretty good.

DxO uses ISO as a proxy for illuminance/luminance (as the formula you linked shows), not metering accuracy. If DSLRs were responding according to the ISO standard, for a given iilluminance/scene luminance, exposure and amplification (ISO) all cameras would record raw values that represent the same percentage of saturation (Studio460 said it well in his post). But they don't.

Hence the potential for 'cheating'. Since ISO is inversely proportional to luminance/illuminance in DxO's world aotbe - and the standards for metering are so loose - all one has to say to look better than the competition is that the measured SNR/DR/TR/CS at a given illuminance/luminance and exposure was obtained with an ISO of 6400, while in fact if that luminance/illuminance were measured according to the 'standard' it would turn out to correspond to a much brighter ISO 3200. Their DxO 'curve' would appear shifted up (better SNR/DR etc.) by one stop. Who's honest and who's not? DxO can tell, and fortunately most manufacturers appear not to be too far off each other. Another way to tell is to do it digitally in post as I suggested above.

Cheers,
Jack

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