DxOMark's measured ISOs vs. manufacturer ISOs

Started Mar 13, 2013 | Discussions thread
Martin.au Forum Pro • Posts: 13,264
Re: DxOMark's measured ISOs vs. manufacturer ISOs

Jack Hogan wrote:

Mjankor wrote:

Jack Hogan wrote: If one camera labelled in-camera ISO settings 1/2, 1, 2, 4, 8 etc. and the other A, B, C, D etc. and you wanted to compare fairly each camera's SNR performance capturing the very same scene subject to the very same artistic constraints, how would you go about choosing the appropriate in-camera ISO setting for both, knowing that the in-camera rendering engine (or raw converter in PP) can make the output image look as bright as one wants?

ISO only. Exposure (f/n and ss) stays fixed, say at f/6.3 1/800, and the same on both cameras.

Well, presumably a nice easy way to do so would be to stop through the ISO values and see which one gives a nice, well exposed final image. Then you could figure out if ISO 2 = ISO B, for example.

We are getting to the heart of the matter. The fact is, both captures are and remain perfectly exposed independently of in-camera ISO settings: we chose that very exposure to give the artistic results that we wanted, and since both cameras were set up with the same f/n and ss, they are both perfectly exposed according to our photographic wishes. you see, exposure is fully defined by shutter speed and f/nuymber, all other things being equal.

But perhaps instead of 'well exposed' you meant to refer to a final image of 'pleasing tonal balance and brightness'. Unfortunately this is immaterial to our quest, because one can make a capture as bright and tonally balanced as one wants in-camera or in-pp - sometimes at the expense of IQ (SNR for this thread). So we do not really care about image brightness other than to ensure that both outputs are about equally bright for comparison purposes. And I can confirm that both of them can be made equally pleasingly bright, independently of the in-camera ISO chosen. Clearly if an inappropriate ISO is chosen, one may look much worse than the other.

So since we can choose any ISO we want while keeping Exposure perfect and unchanged, how do we go about choosing in-camera ISOs to make sure that we are comparing the two camera's noise performance fairly, in the situation described above?

Choose two ISO's that provide a similar 'pleasing tonal balance and brightness', as I stated above.

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