Testing my GH2's sensor

Started Feb 20, 2011 | Discussions thread
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Re: Testing my GH2's sensor
In reply to bg2b, Feb 23, 2011

bg2b wrote:

You've only got 12 bits to work with, so the maximum magnitude of numbers in the RAW file is fixed.

In the case of a simple push (underexpose and then multiply by something > 1), the sensor will be saturated at a lower light level, in particular one that is exactly the push factor lower. For the GH2, DXO says the measured ISO for 160 is 167. If 200 is a digital push by 1/3 of a stop, then it should have a measured ISO of 167*2^(1/3) = 210. DXO says the measured ISO is 209.

In the case of a pull (overexpose and then divide by something > 2), the saturation is determined purely by the higher ISO. For the lower ISO, the top part of the RAW histogram will just be all 0. It's like the well capacity has been reduced by the division factor, so the saturation ISO stays the same; the reduction in gain is exactly cancelled by the effective reduction in well capacity.

Thanks. Crystal clear.

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