Testing my GH2's sensor

Started Feb 20, 2011 | Discussions thread
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bg2b OP Contributing Member • Posts: 897
Re: Testing my GH2's sensor

You measured the signal to noise ratio at different exposures of the sensor? I am only guessing....

Yes, that's basically right.

Take the strongest light/longest exposure that leaves the sensor at just below saturation. Whatever that exposure is defines the true saturation ISO (that's the first thing DXO measures, and the one that leads to endless confusion and accusations of manufacturers cheating, etc.) But if you're working only in RAW, it's what you care about. That level is where your sensor provides the best signal-to-noise ratio, and is the basis for the whole expose-to-the-right business.

After you know the strongest signal, start reducing the exposure. The signal-to-noise ratio will start decreasing. Initially it will decrease by about 3 dB per stop; that's due just to photon shot noise. Once the exposure starts to get low enough, the SNR will start to drop faster because other noise sources (like the analog-to-digital converter noise) will start to make a significant contribution. (If there were no other noise sources, the SNR plot would follow the dashed diagonal line on the graph all the way down.)

That's how the graphs are made; start with the largest non-saturating exposure and then reduce the exposure and plot the SNR at different points.

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