Hi @whwang,
Excellent, transparancy is indeed a multiplicative factor which plays its part.
Creating a normalization method which uses both additive and multiplicative terms for the lokation can be made, but my question would then be:
How to determine which part should be multiplicatively and which part additively. If we have different ISO or gain, I can simply adjust for that internally, but the differences in Light Pollution and or transparancy should be guessed somehow? Are you aware of software that actually does this adequately?
Any reference to any article that discusses these topics would be most welcome ;-)