Dual gain vs base ISO
I've been reading and watching YouTube lately about dual gain sensors. For example the grain on a7IV (a7cII) sensor rises until ISO 400 where it resets to almost ISO 100 level. It starts rising again after the that. A1 sensor resets at 500 ISO and a7III (a7c) sensor resets at 640 ISO.
Then there are different base ISO for different PP.
Are those two related and how can we figure out what combination of PP/ISO will give the cleanest low light photos ?
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From what I gathered sensor dual gain is hardware based, using dual circuitry to process the raw signal from the sensor. The second circuit activates at different ISO depending on the sensor, making it different on different cameras.
The dual ISO based on PP is software based, applying different noise reduction depending on ISO.
How sensor based dual gain and PP based dual ISO interact is quite a mystery !