Testing my GH2's sensor

Started Feb 20, 2011 | Discussions thread
Kolen
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Re: Testing my GH2's sensor
In reply to bg2b, Feb 22, 2011

bg2b wrote:

Look at a RAW-level histogram at the low levels of an exposure. Stick to the low levels because the compression used in RW2 files may not accurately record the low-order bits at high signal levels.

Example from the green channel for part of a scene shot at ISO 160, 200, 250, and 320 with fixed aperture and shutter speeds 1/400, 1/500, 1/640, 1/800. The graphs have the RAW level on the x-axis and the number of pixels with each RAW level on the y-axis. A real ISO will have a filled-in histogram, while an artificial one that's been digitally pushed tends to show peaks and gaps.

Thanks. That's a very professional explanation. It is so confusing so many people on the web make it wrong. I think they merely determine that by guess: 160 sounds like fake from 200. And conventionally people said that the whole number one are real, and skip the one which is 1/3 above it which gives more noise, etc.

But I still have one point that I don't understand, why the measured ISO is different in DxOMark for ISO160 and ISO200? I knew that for E-PL1, for example, ISO100 and ISO200 share the same measured ISO. So, what's the difference in these two cases?
Thanks.

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