Is the E-M5 sensor response nonlinear?

Started Jul 10, 2012 | Discussions thread
Steen Bay
Veteran MemberPosts: 6,188
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Re: A word of advice.
In reply to Iliah Borg, Jul 17, 2012

Iliah Borg wrote:

Do you also see SNR value in highlights being smaller than in midtones?

Don't the SNR values increase rather nicely from 17.14 to 89.78?

The last column is most interesting. Photon noise dominates in midtones and highlights. This type of noise follows Poisson distribution, with dispersion equal to signal. So we can expect that the ratio of the signal to dispersion in midtones and highlights is pretty constant.

But if looking at the 'SNR' ( or 'G2dev') values in column 2, then I don't see any tendency to a lower increase in the highlights than in the midtones. On average the increase is close to the expected 41%, but the single values are all over the place.

17.14
23.35 (+ 36.2%)
35.57 (+ 52.3%)
43.89 (+ 23.4%)
65.26 (+ 48.7%)
89.78 (+ 37.6%)

Anders' method was different though. He used different shutterspeeds and got raw values that were pretty much like they should be (didn't need to worry about flare). Isn't that all we need to know?

I'm not sure whom you refer to saying "we". It is of course not enough for me. If I'm going to shoot ETTR and pull the values back I need to know how much resolution, colour fidelity, noise I'm going to get compared to, say, (ETTR -1 EV) exposure. Once again, practicing ETTR one needs to ask himself why pretty much all the in-camera meters are calibrated to something that is below ETTR.

The contrast/DR of real world scenes/subjects vary wildly, so won't the calibration of the camera's metering always be a compromise? I see people complaining about blown highlights often enough.

Maybe his values were re-linearised under the hood, but if so, isn't that mostly of academic interest?

Noise, resolution, colour fidelity...

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